501 Interchange Design Interchange Design Considerations... 10

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1 5 Interchange Design Table of Contents 51 Interchange Design General Interchange Type Diaond Interchanges Tight Urban Diaond Interchange (TUDI) Single Point Urban Interchange (SPUI) Diaond Interchange with Roundabouts Diverging Diaond Interchange (DDI) Cloverleaf Interchange Partial Cloverleaf Interchange Directional Interchanges Interchange Design Considerations Deterination of Interchange Configuration Approaches to the Structure Alignent, Profile and Cross Section Sight Distance Interchange Spacing Unifority of Interchange Patterns Route Continuity Signing and Marking Basic Nuber of Lanes Coordination of Lane Balance and Basic Nuber of Lanes Auxiliary Lanes Lane Reductions Weaving Sections Interchange Rap Design General Rap Design Speed Diaond Rap Design Speeds Loop Rap Design Speeds Directional Rap Design Speeds Vertical Alignent Horizontal Alignent January 219

2 5 Interchange Design 53.5 Rap Terinals General Considerations Left-hand Entrances and Exits Distance Between Successive Rap Terinals Single-Lane Rap Terinals Terinal Classification Single-Lane Entrance Terinals High-Speed Low-Speed Single-Lane Exit Terinals High-Speed Low-Speed Superelevation at Terinals Terinals on Crest Vertical Curves Rap At-Grade Intersections Collector - Distributor (C-D) Roads Use of C-D Roads Design of C-D Roads C-D Road Entrance and Exit Terinals Multi-lane Rap & Roadway Terinals and Transitions Multi-lane Entrance Raps and Converging Roadways General Lane Balance and Continuity Inside Merges Preferential Flow Horizontal Curvature Crest Vertical Curves Superelevation and Joint Location Multi-lane Exit Raps and Diverging Roadways General Lane Balance and Continuity Terinal Design Horizontal Curvature Crest Vertical Curves Superelevation and Joint Location Four Lane Divided to Two Lane Transition Service Roads Use of Service Roads Design of Service Roads January 219

3 5 Interchange Design 55 Requests for New or Revised Access Interstate Highways or Other Freeways General Interchange Study (Access Point Request Docuent) Interchange Operations Study (IOS) Safety Iproveents on Interstate or Other Freeways Study Methodology General Constrained Traffic Diagras and Plans Subission of Interchange Studies Review of Interchange Studies LIST OF FIGURES January 219

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5 5 Interchange Design 51 INTERCHANGE DESIGN 51.1 General An interchange is defined as a syste of interconnecting roadways in conjunction with one or ore grade separations that provides for the oveent of traffic between two or ore roadways or highways on different levels. Interchanges are utilized on freeways and expressways where access control is iportant. They are used on other types of facilities only where crossing and turning traffic cannot be accoodated by a noral at-grade intersection. An Interchange Justification Study ay be necessary Interchange Type The ost coonly used types of interchanges are the diaond, cloverleaf and directional Diaond Interchanges The diaond interchange is the ost coon type where a ajor facility intersects a inor highway. The design allows free-flow operation on the ajor highway but creates at-grade intersections on the inor highway with the raps. Traffic control at the at-grade intersections can be stop, signal or roundabout. The capacity of a diaond interchange is liited by the at-grade intersections on the inor highway. Variations of the diaond interchange include but are not liited to the Tight Urban Diaond Interchange (TUDI), the Single Point Urban Interchange (SPUI) and the Diverging Diaond Interchange (DDI) Tight Urban Diaond Interchange (TUDI) The TUDI, a type of copressed diaond interchange, is used in urban and suburban areas where right of way is liited. This interchange design has two closely spaced signalized rap intersections. Special signal phasing allows queuing of vehicles outside the rap intersections and eliinates queuing of vehicles between the rap intersections. Typical designs provide 25 to 4 feet of separation between the signalized intersections. The key operational aspect of a TUDI is one controller running both intersections ipleenting the Texas Diaond 4 Phase operation. The single controller that runs both raps can be coordinated with adjacent intersections, but the two rap signals are on one controller. The 4 phase sequence is used when queue storage between the rap intersections is critical as it tends to not store any vehicles between the two rap intersections. A TUDI ay not need to ipleent Texas Diaond 4-Phase operation. Geoetric constraints ay warrant the construction of a TUDI, but operational benefits of the Texas Diaond Phasing ay not be needed and conventional signal phasing can be used Single Point Urban Interchange (SPUI) January

6 5 Interchange Design The SPUI, is another variation of the copressed diaond interchange. It was developed to strealine operations by using a single traffic signal to control traffic oveents within the interchange area. The SPUI also requires less right-of-way than a conventional diaond interchange. I-27 & Sawill Road SPUI (Google) A SPUI should be considered: In areas with liited right-of-way. At locations with heavy left turn volues both on and off the raps. At locations where a wider structure or intersection can be accoodated. SPUIs offer the following benefits: Construction in a relatively narrow right-of-way, resulting in potentially significant cost reductions. Since the SPUI has only one intersection, as opposed to two for a diaond interchange, the operation of the single traffic signal on the crossroad ay result in reduced delay through the intersection area when copared to a diaond interchange. Iproved safety since vehicles only cross paths at one intersection instead of two. Right turn oveents both on and off the raps are typically free flow or yield control. Only the left turns pass through the signalized intersection. As a result, a ajor source of traffic conflict is eliinated, increasing overall intersection efficiency and reducing the traffic signal phasing needed fro four-phase to three-phase operation. The turning angle and curve radii for left-turn oveents through the intersection are significantly flatter than at conventional intersections and, therefore, the left turns ove at higher speeds. The left turn angle is typically 45 to 6 degrees with a iniu radius of 15 to 2 ft. The above-entioned operations ay result in a higher capacity than a conventional tight diaond interchange. Liitations/disadvantages of a SPUI include: January

7 5 Interchange Design Construction costs of SPUIs tend to be uch higher than conventional diaond interchanges due to costs associated with the bridges. Overpass SPUIs need long bridges to span the large intersection below. A two-span structure is not a design option because a center colun would conflict with traffic oveents. Single-span overpass bridges are typically 22 ft in length, while three-span bridges often exceed 4 ft. The SPUI underpass tends to be wide and often is butterfly in shape. Rectangular SPUI structures, while resulting in unused deck area, ay provide additional area for aintenance of traffic and siplified construction. Where right-ofway is constrained, SPUIs typically utilize extensive retaining walls, further adding to the cost. However, the higher construction cost of SPUIs is often offset by the reduced right-of-way cost. A potential disadvantage of SPUIs is the length and geoetry of the path for left-turning vehicles through the intersection. Like ost typical intersections, left-turning vehicles pass to the left of opposing left-turning vehicles. However, due to the size and distance between opposing approaches, the path of left-turning vehicles does not reseble a quarter of a circle found at typical intersections, but rather resebles a quarter of an ellipse. To provide positive guidance for this non-traditional path, at a iniu, dashed lane lines should be painted through the intersection. A skew angle between the two roadway alignents has an adverse effect on SPUIs because it increases clearance distances and adversely affects sight distance. Severe skew in alignents ay also increase the length of the bridge and widen the distance between the stop bars on the local streets. Extree care should be exercised in planning SPUIs when the skew angle approaches 3 degrees. It is iportant to provide visibility between exit rap traffic and cross street traffic approaching fro the left. For left-turn oveents fro the ainline s rap to the cross street, provide a clear cornering sight line with no obstructions fro bridge abutents, pilasters, signal/light poles, signing, or landscaping. Design considerations of a SPUI include: It is desirable that the left-turn curve be a single radius. This will, however, typically result in additional right-of-way, a larger bridge structure, or both. Where it is not practical to provide a single radius and curves are copounded fro a larger to a saller radius, the second curve should be at least half the radius of the first. Stopping sight distance should be provided on the left-turn oveents equal to or exceeding the design speed for the curve radius involved. Additional edian width on the cross street can iprove intersection operation. The stop bar location on the cross street is dependent on the wheel tracks fro the opposing rap left-turn oveent. By widening the edian, the stop bar on the cross street can be oved forward, thus reducing the size of the intersection and the distance each vehicle travels through the intersection. The results include greater available green tie and less potential driver confusion due to an expansive intersection area. A iniu clear distance of 1 ft between opposing left turns within the intersection should be provided. Pedestrian crossing of the local street at rap terinals typically adds a signal phase and uses considerable green tie, resulting in reduced operational efficiency. Therefore, the overall design should include provision for pedestrian crossings at adjacent intersections instead of at the rap terinal intersection. Right-turn lanes at SPUIs are typically separated fro the left-turn lanes, often by a considerable distance. The exit rap right turn can be a free or controlled oveent. The design of free right turns should include an additional lane on the cross street beginning at the free right-turn lane for at least 3 ft before being erged. Free-flow right turns fro the exit rap to the crossroad ay or ay not be desirable depending on the traffic operational analysis which includes the downstrea intersection(s) of the crossroad. There ay be inadequate weaving distance January

8 5 Interchange Design between the exit rap and the adjacent intersection. Where the right-turn oveent is controlled by a stop sign or traffic signal, adequate right-turn storage on the exit rap should be provided to prevent blockage of vehicles turning left or traveling straight. Free-flow right turns on entrance raps pose little operational concern, assuing adequate erge length is provided on the entrance rap. The right-turn lane should extend at least 3 ft beyond the convergence point before beginning the erge Diaond Interchange with Roundabouts Roundabout interchanges utilize roundabouts at either one or both rap intersections. Additional bridge width is usually not necessary at roundabout interchanges due to the eliination of turn lanes. The benefits and costs associated with this type of interchange also follow those for a single roundabout. Roundabouts ay be a good alternative if the interchange has a high proportion of left turn flows fro the off raps and to the on raps during peak periods, cobined with liited queue storage space on the bridge crossing, off-raps, or arterial approaches. In such circustances, roundabouts operating within their capacity are particularly useful in solving these probles when copared with other fors of intersection control. The raindrop roundabout interchange design exhibits very little queuing between the intersections since these oveents are alost unopposed. Therefore, the approach lanes across the bridge can be iniized. On the other hand, drivers do not have to yield when approaching fro the connecting roadway between the two roundabouts. If the roundabout is designed poorly, drivers ay be traveling faster than they should to negotiate the next roundabout safely. The designer should analyze relative speeds to evaluate this alternative. A potential benefit of roundabout interchanges is that the queue length on the off-raps ay be less than at a signalized intersection Diverging Diaond Interchange (DDI) The Diverging Diaond Interchange (DDI) is a variation of a conventional diaond interchange. The DDI uses directional crossover intersections to shift traffic on the cross street to the left-hand side between the rap terinals within the interchange. Crossing the through oveents to the opposite side replaces left-turn conflicts with sae-direction erge/diverge oveents and eliinates the need for exclusive left-turn signal phases to and fro the rap terinals. All connections fro the raps to and fro the cross street are joined outside of the cross-over intersections, and these connections can be controlled by two-phase signals, have stop or yield control, or be free flowing. A DDI should be considered: At locations where there is liited roadway width for left-turns between rap intersections and liited right-of-way to expand. At locations with heavy left turn volues both on and off the raps. At locations without adjacent traffic signals or nearby driveways. The DDI offers the following benefits: Iproved safety due to the reduction in the nuber of conflict points (locations where vehicle paths cross), vehicle-to-vehicle, vehicle-to-pedestrian and vehicle-to-bike. January

9 5 Interchange Design By allowing the rap-terinal intersections to operate with siple, two-phase signal operations, the design provides flexibility to accoodate a greater volue of traffic and operate with less delay. Overall operations of a DDI ay be greater copared to a conventional signalized diaond interchange due to shorter cycle lengths, reduced tie lost per cycle phase, reduced stops and delay, and shorter queue lengths. The DDI also reduces the nuber and severity of conflict points for both otorized and nonotorized users. The crossing distances for pedestrians are coparatively shorter, and usually involve traffic approaching fro only one direction at a tie. The cross-sectional characteristics of a DDI provide ultiple options for facilitating convenient pedestrian and bicycle oveents, and the geoetry of the crossover intersections have an added benefit of reducing otorized vehicle speeds through the interchange, resulting in a traffic caling effect which ay reduce crashes. Retrofitting an existing conventional diaond interchange to a DDI ay be less costly than options involving widening the crossroad near the interchange (including widening the bridge) and adding additional lanes to the raps. For new interchanges, the operational efficiency of a DDI ay allow for a saller structural footprint since fewer lanes are generally needed to accoodate the traffic deands. In soe contexts, the DDI ay allow for reduced right-of-way needs and construction costs copared to other interchange fors. The large channelizing islands help reduce wrong-way oveents onto the exit raps. Accoodates either overpass or underpass designs. I-27 & Roberts Road DDI (District 6) January

10 5 Interchange Design Liitations/Disadvantages of a DDI include: Crossing traffic to the wrong side of the road ay not eet driver expectations. A DDI does not allow free flowing traffic on the crossroad in both directions since the signals cannot be green at both intersections for both directions at the sae tie. The potential operational benefits of the DDI rap intersections ay be overshadowed by poor operational perforance of nearby signals on the crossroad. If an adjacent signal is too close and the queue storage length is inadequate, the traffic spillback ay inhibit the oveent of traffic along the crossroad, and potentially block traffic fro the exit raps. The DDI design does not accoodate typical up and over exit to entrance oveents for oversized vehicles or authorized vehicles during aintenance or eergency situations. Crossroads that are heavily skewed to the ain facility typically need greater intersection spacing. Design considerations for a DDI include: It ay be advantageous to use ultiple structures at the grade separation, especially where the skew angle between facilities is significant. The spacing between rap intersections will ipact signal design and operations on the crossroad corridor but very tight spacing between rap intersections ay constrain the design of the crossovers and liit queue storage and signal tiing options. The proxiity to a DDI of adjacent signalized intersections along the crossroad ay ipact the perforance of the DDI at a given location. Modifications to adjacent signalized intersections along the crossroad ay be necessary to aintain the overall signal progression along the corridor and reduce potential effects of queue spillback. The through oveent queues need to be checked at the crossovers for blockage of the freeflowing left and right turns to and fro the raps. Auxiliary lanes ay be needed for the turn lanes if blockage occurs. Design speeds for crossover alignents should be in the range of 2 to 35 ph, resulting in crossover radii in the range of 1 to 5 ft. Cross slopes are typically in the range of plus or inus 2 percent. Higher approach speeds need to be lowered to the crossover design speeds with advance warning signs and geoetric features (reverse curves, etc.). 1 ft of tangent between the reverse curves through the crossover should be provided in both directions. The tangent helps to aintain the desired vehicle tracking and the curve-tangentcurve sequence prootes driving at the desired target speed. Radii at the exit and entrance rap oveents are like other interchanges and include allowance for the turning path of the design vehicle, sight distance, pedestrians, bicycles and the intersection traffic control type. The crossing angle is the acute angle between lanes of opposing traffic within the crossover based on the tangent sections. The greater the crossover angle, the ore the crossover will appear like a noral intersection of two different cross routes and decrease the likelihood of a driver aking a wrong-way oveent. However, greater crossing angles generally result in larger footprints. Larger crossing angles in cobination with sharp reverse curves can increase the potential for overturning of vehicles with high centers of gravity and excessive driver discofort through the crossovers. The recoended approach is to attain the largest crossing angle possible that is in balance with the other geoetric paraeters and site constraints. The crossover angle of a DDI is generally between 4 to 5 degrees. Crossover angles less than 3 degrees ay increase the potential for wrong-way oveents. January

11 5 Interchange Design Lane widths along the crossroad of a DDI typically range fro 12 to 15 ft depending on site location and consideration for design vehicles traveling side by side through the crossover area. The wider lane width typically occurs prior to and after the crossover curves. The additional lane width does not need to be continued between the two crossovers. The shoulders required by the crossroad should also be provided through the DDI. The outside shoulder becoes the inside shoulder within the interchange between the crossover intersections. Sight distance at DDIs is iportant for both vehicles aneuvering through the crossovers or turning left and right fro the rap terinals onto the cross street, especially when the turning rap terinal traffic is under yield control. The FHWA Diverging Diaond Interchange Inforational Guide provides additional inforation on diverging diaond interchanges Cloverleaf Interchange Cloverleaf designs ay be used in lieu of a diaond when a continuous flow design is required where two ajor facilities intersect. In this case, a full cloverleaf interchange is the iniu design that can be used. The designer should consider collector-distributor roads in conjunction with cloverleaf interchanges to iniize weaving. Full Cloverleaf Interchange I-27/East Main Street (Google) However, full cloverleafs have deficiencies which need to be addressed before being chosen as the interchange type. Principle disadvantages are: The inherent weaving aneuver generated and the short weaving length available. January

12 5 Interchange Design Large trucks ay not be able to operate efficiently on the saller curve radii on the associated loop raps. Loop raps are liited in capacity. When Collector-Distributor roads are not used, a further disadvantage includes weaving on the ain line, the double exit on the ain line and probles associated with signing for the second exit. The full cloverleaf weaving aneuver is not objectionable when the left-turning oveents are relatively light, but when the su of traffic volues on two adjoining loops approaches about 1, vehicles per hour, interference occurs, which results in a reduction in the speed of the ainline traffic. When the weaving volue in a particular section exceeds 1, vehicles per hour, the quality of service on the ain facility deteriorates, generating a need to transfer the weaving section fro the through lanes to a C-D road. For these reasons, full cloverleafs are discouraged Partial Cloverleaf Interchange Partial cloverleaf designs ay be used in lieu of a diaond when developent or other physical conditions prohibit construction in a quadrant, or where heavy left turns are involved. In the design of partial cloverleafs, the site conditions ay offer a choice of quadrants to use. However, at a particular interchange site, topography and culture ay be the factors that deterine the quadrants in which the raps and loops can be developed. There is considerable operational advantage in certain arrangeents of raps. These are discussed and suarized below. Raps should be arranged so that the entrance and exit turns create the least ipedient to the traffic flow on the ajor highway. The following guidelines should be considered in the arrangeent of the raps at partial cloverleafs: The rap arrangeent should enable ajor turning oveents to be ade by right-turn exits and entrances. Where through-traffic volue on the ajor highway is decidedly greater than that on the intersecting inor road, preference should be for an arrangeent that places the right turns (either exit or entrance) on the ajor highway, even though this results in a direct left turn off the crossroad. These controls do not always lead to the ost direct turning oveents. Instead, drivers frequently ay need to first turn away fro or drive beyond the road that is their intended destination. Such arrangeents cannot be avoided if the through-traffic oveents, for which the separation is provided, are to be facilitated to the extent practical. January

13 5 Interchange Design Partial Cloverleaf A Interchange (4 Quadrant ParClo A) I-27/Georgesville Road (Google) The ParClo A layout has loop raps that are in diagonally opposite quadrants and the raps are on the near side of the structure as drivers approach on the ajor road. Preferred for a high volue of leftturns fro the crossroad to the ainline. Weaving between the loop raps is eliinated. Partial Cloverleaf B Interchange (2 Quadrant ParClo B) I-71/SR48 (Google) The ParClo B layout has loop raps that are in diagonally opposite quadrants and the raps are on the far side of the structure as drivers approach on the ajor road. Preferred for a high volue of left-turns fro the ainline to the crossroad. Weaving between the loop raps is eliinated. January

14 5 Interchange Design For additional inforation and types of Partial Cloverleaf Interchanges, see the AASHTO Green Book, Chapter Directional Interchanges Directional interchanges are the highest type and ost expensive. They perit vehicles to ove fro one ajor freeway to another ajor freeway at relatively fast and safe speeds. 52 INTERCHANGE DESIGN CONSIDERATIONS 52.1 Deterination of Interchange Configuration Interchange configurations are covered in two categories, syste interchanges and service interchanges. The ter syste interchange is used to identify interchanges that connect two or ore freeways, whereas the ter service interchange applies to interchanges that connect a freeway to lesser facilities. Generally, interchanges in rural areas are widely spaced and can be designed on an individual basis without any appreciable effect fro other interchanges within the syste. However, the final configuration of an interchange ay be deterined by the need for route continuity, unifority of exit patterns, single exits in advance of the separation structure, and eliination of weaving on the ain facility, signing potential, and availability of right-of-way. Selecting an appropriate interchange configuration in an urban environent involves considerable analysis of prevailing conditions so that the ost practical interchange configuration alternatives can be developed. Generally, in urban areas, interchanges are so closely spaced that each interchange ay be influenced directly by the preceding or following interchange to the extent that additional traffic lanes ay be needed to satisfy capacity, weaving and lane balance. Interchanges should provide for all oveents, even when an anticipated turning oveent volue is low. Once several alternates have been prepared for the syste design, they can be copared on the following principles: (1) capacity, (2) route continuity, (3) unifority of exit patterns, (4) single exits in advance of the separation structure, (5) with or without weaving, (6) potential for signing, (7) cost, (8) availability of right-of-way, (9) constructability, and (1) copatibility with the environent Approaches to the Structure Alignent, Profile and Cross Section Traffic passing through an interchange should be afforded the sae degree of utility and safety as that given on the approaching roadways. The design speed, alignent, profile and cross section in the interchange area should be consistent with those on the approaching highways. Four-lane roadways should be divided at interchanges with a non-traversable edian to ensure that drivers use the proper raps for left-turning aneuvers. At-grade left turns preferably should be accoodated within a suitably wide edian. January

15 5 Interchange Design Sight Distance Sight distance on the roadways through an interchange should be at a iniu the required stopping sight distance and preferably should be Decision Sight Distance (Figure 21-6), particularly along entrances and exits. The horizontal sight distance liitations of piers and abutents at curves usually present a ore difficult proble than that of vertical liitations. With the iniu radius for a given design speed, the noral lateral clearances at piers and abutents of underpasses does not provide the iniu stopping sight distance. Siilarly, on overpasses with the sharpest curvature for the design speed, sight distance deficiencies result fro the usual offset to the bridge railing. Above iniu radii should be used for curvature on roadways through interchanges. If sufficiently flat curvature cannot be used, the clearances to abutents, piers or bridge railing should be increased to obtain the proper sight distance, even though this involves increasing structure spans or widths Interchange Spacing Interchanges should be located close enough together to properly discharge and receive traffic fro other highways or streets, and far enough apart to perit the free flow and safety of traffic on the ain facility. In general, ore frequent interchange spacing is peritted in urbanized areas. Miniu spacing is deterined by weaving requireents, ability to sign, lengths of speed change lanes, and capacity of the ain facility. Interchanges within urban areas should not be spaced closer than an average of 2 iles, in suburban sections an average of not closer than 4 iles, and in rural sections an average of not closer than 8 iles. In consideration of the varying nature of the highway, street or road systes with which the freeway or expressway ust connect, the spacing between individual adjacent interchanges ust vary considerably. In urban areas, the iniu distance between adjacent interchanges should not be less than 1 ile, and in rural areas not less than 3 iles. Spacing less than this have a detriental effect on freeway operations Unifority of Interchange Patterns Since interchange unifority and route continuity are interrelated concepts, interchanges along a freeway should be reasonably unifor in geoetric layout and general appearance to provide the appropriate level of service and axiu safety in conjunction with freeway operations. Except in highly special cases, all entrance and exit raps should be on the right Route Continuity Route continuity is an extension of the principle of operational unifority coupled with the application of proper lane balance and the principle of aintaining a basic nuber of lanes. The principle of route continuity siplifies the driving task in that it reduces lane changes, siplifies signing, delineates the through route and reduces the driver s search for directional signing. Desirably, the through driver should be provided a continuous through route on which changing lanes is not necessary to continue on the through route. In aintaining route continuity, interchange configuration ay not always favor the heavy traffic oveent, but rather the through route. In this situation, heavy oveents can be designed on flat curves with reasonably direct connections and auxiliary lanes. January

16 5 Interchange Design 52.6 Signing and Marking The safety, efficiency and clarity of paths to be followed at interchanges depend largely on their relative spacing, geoetric layout and effective signing and arking. The location of and iniu spacing between rap terinals depends to a large degree on whether or not effective signing can be provided. Signing and arking should confor to the OMUTCD Basic Nuber of Lanes The basic nuber of lanes is defined as a iniu nuber of lanes designated and aintained over a significant length of a route, irrespective of changes in traffic volue and lane balance needs. (The basic nuber of lanes is a constant nuber of lanes assigned to a route, exclusive of auxiliary lanes, based on capacity needs of the section.) 52.8 Coordination of Lane Balance and Basic Nuber of Lanes Design traffic volues and a capacity analysis deterine the basic nuber of lanes to be used on the freeway and the iniu nuber of lanes on the raps. The basic nuber of lanes should be established for a substantial length of freeway and should not be changed through pairs of interchanges, siply because there are substantial volues of traffic entering or leaving the freeway. There should be continuity in the basic nuber of lanes. Auxiliary lanes should be provided for variations in traffic deand. After the basic nuber of lanes is deterined for each roadway, the balance in the nuber of lanes should be checked on the basis of the following principles: 1. At entrances, the nuber of lanes beyond the erging of two traffic streas should not be less than the su of all traffic lanes on the erging roadways inus one, but ay be equal to the su of all traffic lanes on the erging roadways. 2. At exits, the nuber of approach lanes on the roadway should be equal to the nuber of lanes on the roadway beyond the exit, plus the nuber of lanes on the exit, inus one. Exceptions to this principle occur at cloverleaf loop rap exits that follow a loop rap entrance and at exits between closely spaced interchanges. In these cases, the auxiliary lane ay be dropped in a single-lane exit with the nuber of lanes on the approach roadway being equal to the nuber of through lanes beyond the exit plus the lane on the exit. 3. The traveled way of the highway should be reduced by not ore than one traffic lane at a tie Auxiliary Lanes An auxiliary lane is the portion of the roadway adjoining the traveled way for speed change, turning, storage for turning, weaving and other purposes suppleentary to through-traffic oveent. An auxiliary lane ay be provided to coply with the concept of lane balance, to coply with capacity needs or to accoodate speed changes, weaving and aneuvering of entering or exiting traffic. January

17 5 Interchange Design 52.1 Lane Reductions The basic nuber of ainline lanes should not be reduced through a service interchange. If a reduction in the basic nuber of lanes is warranted by a substantial decrease in traffic volue over a significant length of freeway, then it should be reduced between interchanges. The reduction should occur 2, to 3, ft. fro the end of the acceleration taper of the previous interchange to allow for adequate signing. The end of the lane reduction should be tapered at a rate of 7:1. The lane reduction should occur on a tangent section of freeway, preferably within a sag vertical curve, and provide Decision Sight Distance, Figure 21-6, where possible. The lane reduction should also be on the right side of the freeway Weaving Sections Weaving sections are highway segents where the pattern of traffic entering and exiting at contiguous points of access results in vehicle paths crossing each other. Weaving sections ay occur within an interchange, between closely spaced interchanges or on segents of overlapping routes. Because weaving sections cause considerable turbulence which results in a reduction in capacity, interchange designs that eliinate weaving or reove it fro the ainline by the use of C-D roads are desirable. The capacity of weaving sections ay be seriously restricted unless the weaving section has adequate length, adequate width and lane balance. Refer to the Highway Capacity Manual for capacity analysis of weaving sections. 53 INTERCHANGE RAMP DESIGN 53.1 General An interchange rap is a roadway which connects two legs of an interchange. Rap cross section eleents are discussed in Section Eleents contributing to horizontal and vertical alignents are designed siilar to any roadway (Section 2) once the rap design speed has been deterined Rap Design Speed In order to design horizontal and vertical alignent features, a design speed ust be deterined for each rap. Since the driver expects a speed adjustent on a rap, the design speed ay vary within the rap liits. Figure 53-1 includes three ranges of rap design speeds which vary with the design speed of the ainline roadway. The rap design speed range is deterined by engineering judgent based on several conditions: 1. The type of roadways at each end of the rap and their design speeds, 2. The length of the rap, January

18 5 Interchange Design 3. The terinal conditions at each end, and 4. The type of rap (diaond, loop or directional). Design exceptions will be required for speed related design criteria that do not eet the following: For directional raps (roadways) that do not provide the iniu design speed given in Section For loop raps on high-speed roadways that do not provide a iniu design speed of 25 ph (15-ft radius). For all other raps that, at a iniu, do not provide the lower range design speed of Figure Diaond Rap Design Speeds Diaond raps norally have a high speed condition at one end and an at-grade intersection with either a stop or slow turn (15 ph) condition at the other. Upper to iddle range design speeds in Figure 53-1 are noral near the high speed facility with iddle to lower range design speeds usually used closer to the at-grade intersection Loop Rap Design Speeds Loop raps ay have a high speed condition at one end and, either a slow or high speed condition at the other. Loop raps, because of their short radius, usually have design speeds in the lower range in the iddle and slow speed end of the rap with iddle range design speeds occasionally used nearer the high speed terinal. For design speeds, see Figure The iniu loop rap radius is 15 feet (5 ) Directional Rap Design Speeds Directional raps (roadways) generally have high speed conditions at both ends. They are norally designed using a design speed falling into the upper range of Figure The absolute iniu should be the iddle range design speeds Vertical Alignent Maxiu grades for vertical alignent cannot be as definitely expressed as for the highway, but should preferably not exceed 5 percent. General values of liiting upgrades are shown in Table 53-1, but for any one rap the grades to be used are dependent upon a nuber of factors. These factors include the following: 1. The flatter the gradient on the rap relative to the freeway grade, the longer the rap will be. 2. The steepest grades should occur over the center part of the rap. Grades at the terinal ends of the rap should be as flat as possible. 3. Short upgrades of 7 to 8 percent perit good operation without unduly slowing down passenger cars. Short upgrades of as uch as 5 percent do not unduly affect trucks and buses. January

19 5 Interchange Design 4. Rap grades and lengths can be significantly ipacted by the angle of intersection between the two highways when the angle is 7 degrees or less. The direction and grade on the two highways ay also have a significant ipact. 5. Adequate sight distance is ore iportant than a specific gradient control and should be favored in design. Table 53-1 Maxiu Rap Upgrades Rap Design Speed 25-3 ph 35-4 ph 45 ph and above Desirable Grade (%) Maxiu Grade (%) Note: Downgrades ay exceed the table values by 2%, but should not exceed 8% Horizontal Alignent Horizontal alignent will be largely deterined by the selected design speed and type of rap. The horizontal alignent criteria found in Section 22 shall also apply to raps. Check that the required horizontal stopping sight distance is provided. Use the allowed skew at the rap terinal at-grade intersection to iniize curvature. Depending on the design speed and curvature, curve widening ay be required on a two-lane rap. See Section and Figure 31-5c. The WB-62 [WB-19] design vehicle should be used for Interstate raps Rap Terinals The terinal of a rap is that portion adjacent to the through traveled way, including speed change lanes, tapers and islands. Rap terinals, as opposed to diverging roadways, require speed change lanes. Rap terinals ay be the at-grade type, as at the crossroad terinal of diaond or partial cloverleaf interchanges, or the free-flow type where rap traffic erges with or diverges fro high-speed through traffic at flat angles. Terinals are further classified as either single-lane or ulti-lane and as either a taper or parallel type General Considerations While interchanges are custo designed to fit specific site conditions, it is desirable that the overall pattern of exits along the freeway have soe degree of unifority. It is desirable that all interchanges have one point of exit located in advance of the crossroad wherever practical. January

20 5 Interchange Design Because considerable turbulence occurs throughout weaving sections, interchange designs that eliinate weaving entirely or at least reove it fro the ainline are desirable. Weaving sections ay be eliinated fro the ainline by the incorporation of C-D roadways or grade separating the raps (braiding). Interchanges that provide all exit oveents before any entrance oveents will also eliinate weaving and are highly recoended Left-hand Entrances and Exits Left-hand entrances and exits are contrary to the concept of driver expectancy when interixed with right-hand entrances and exits. Therefore, extree care should be exercised to avoid left-hand entrances and exits in the design of interchanges. Because they are contrary to driver expectancy, special attention should be given to signing and the provision for decision sight distances to alert the driver an unusual condition exists Distance Between Successive Rap Terinals In urban areas rap terinals are often located in close succession. To provide sufficient weaving length and adequate space for signing, a reasonable distance should be provided between successive rap terinals. Spacing between successive outer rap terinals is dependent on the classification of the interchanges involved, the function of the rap pairs (entrance or exit), and weaving potential. Miniu spacing for various rap cobinations are shown in Figure 53-1a. Where an entrance rap is followed by an exit rap, that absolute iniu distance between the successive noses is governed by weaving considerations. This spacing is not applicable to cloverleaf interchanges as the distances between entrance-exit raps noses is dependent on loop rap radii and other factors. When the distance between successive noses is less than 1,5 ft. the speed change lanes should be connected to provide an auxiliary lane to iprove traffic flow over a relatively short section of the freeway Single-Lane Rap Terinals This discussion is liited to terinals used for single-lane entrance and exit raps only. See Section 55 for ulti-lane transitions. Ohio s standards currently perit a parallel exit terinal and tapered entrance terinal Terinal Classification Ohio uses two basic rap terinal classifications. High-Speed Terinals (See Figures 53-2a, 53-2b and 53-2c, along with Figures 53-3a, 53-3b and 53-3c) - High-Speed terinals are intended for use on all Interstate highways and on other liited access freeways or expressways having siilar design standards and a iniu ainline design speed of 5 ph. January

21 5 Interchange Design Low-Speed Terinals (See Figures 53-4a and 53-4b) - Low-Speed terinals (ainline design speeds of 45 ph or less) are intended for use on all other liited access expressways or other highways which have little or no access control except through an interchange area. Many of the features of Low-Speed terinals are applicable to a terinal of one rap with another rap. Low Speed terinals are also used with Low-Speed C-D Roads Single-Lane Entrance Terinals High-Speed The typical single-lane entrance terinal consists of two parts, an acceleration lane and a taper. The acceleration lane allows the entering vehicle to accelerate to the freeway speed and evaluate gaps in the freeway traffic. The taper is provided for the entering vehicle to erge into the chosen gap in freeway traffic. The iniu taper rate is 5:1. The length of the acceleration lane varies depending on the design speed of the last rap curve on the entrance rap and the design speed of the ainline. Figure 53-2a provides the iniu lengths of acceleration lanes for entrance rap terinals. When the average grade of the acceleration lane exceeds 3%, the acceleration length obtained fro Figure 53-2a should be adjusted by the factor obtained fro Figure 53-2b. The acceleration lane length is easured fro the last entrance rap curve point (PT or CS) to the point where the right edge of traveled way of the rap is 12 feet fro the right edge of the through traveled way of the freeway. Figure 53-2c illustrates the typical design of a single-lane entrance rap terinal. If the entrance terinal results in an add-lane (no erge), delete the last 6 of the 5:1 taper of Figure-53-2c. All other entrance terinal diensions of Figure 53-2c reain the sae. Referring to Figure 53-2c, when the required acceleration length (L fro Figure 53-2a, adjusted to grade, Figure 53-2b) is less than the acceleration length provided by the 2 ft. spiral plus 65 ft. of the 5:1 taper, then a parallel acceleration length is not required and the terinal becoes the iniu acceptable design consisting of the 2 ft. spiral and the 1,25 ft. 5:1 taper Low-Speed Figure 53-4a provides the Low-Speed Entrance Terinal designs for ainline design speeds equal to or less than 45 ph Single-Lane Exit Terinals High-Speed The typical single-lane exit terinal consists of two parts, a taper for aneuvering out of the through traffic lane and a deceleration lane to slow to the speed of the first curve on the rap. All deceleration should occur on the full width deceleration lane and not on the ainline or the taper. The length of the deceleration lane varies depending on the design speed of the ainline and the design speed of first geoetric control on the exit rap, usually a horizontal curve but could be the stopping sight distance on a vertical curve or the back of an anticipated traffic queue. Figure 53-3a provides the iniu lengths of deceleration lanes for exit rap terinals. When the average grade of the January

22 5 Interchange Design deceleration lane exceeds 3 percent, the deceleration length obtained fro Figure 53-3a should be adjusted by the factor obtained fro Figure 53-3b. The deceleration lane length is easured fro the point where the taper reaches a width of 12 feet to the first point that governs the design speed of the exit rap, usually the PC of the first curve. Figure 53-3c illustrates the typical design of a single-lane exit rap terinal. The iniu deceleration length (Figure 53-3a) adjusted to grade (Figure 53-3b) shall be 8 ft Low-Speed Figure 53-4b provides the Low-Speed Exit Terinal design for ainline design speeds equal to or less than 45 ph Superelevation at Terinals Superelevation at rap terinals should be developed using the following guidelines: The rate of superelevation at the entrance and exit nose shall be selected on the basis of the design speed of the rap at the nose. All transverse changes or breaks in superelevation shall be ade at joint lines (See Standard Construction Drawing BP-6.1). In the case of bituinous paveent, the superelevation breaks should occur in the sae locations as they would in concrete paveent. For High-Speed terinals, the transverse breaks in superelevation cross-slope shall not exceed a differential of.32 at the ainline edge of traveled way or.5 at other locations. If a double break occurs on longitudinal joints less than 6 ft. apart, it shall not exceed a total differential of.32, if adjacent to the ainline, or.5 elsewhere. On Low-Speed terinals the transverse breaks in superelevation cross-slope shall not exceed a differential of.5 to.6. For High-Speed terinals, the rate of rotation of a superelevated rap paveent or speed change lane paveent shall be in accordance with Section Where possible, the terinal area paveent and shoulder should slope away fro the ainline paveent so that a iniu aount of water drains across the ainline paveent Terinals on Crest Vertical Curves Mainline crest vertical curves in the vicinity of rap terinals should be designed using decision stopping sight distances. When it is not feasible to provide decision stopping sight distance, at a iniu, 125% SSD (Figure 21-1) should be provided. Where a crest vertical curve occurs on an exit rap at or near the nose, the crest vertical curve should be designed using the "upper range" design speeds of Figure Rap At-Grade Intersections Rap at-grade intersections are designed using uch of the sae criteria as outlined in Section 41 (the noral design vehicle for Interstate raps is the WB-62 [WB-19]). However, one of the basic differences is the one-way nature of raps and the fact that ost traffic at rap intersections is turning. Figure January

23 5 Interchange Design 53-5 shows the design of a typical uncurbed rap intersection. Curbed returns are norally used in urban areas where space is ore restricted. Intersection Sight Distance, Section 21.3, should be provided at all rap at-grade intersections. Exit raps ay require ultiple lanes at the crossroad intersection to provide additional storage and capacity. Figure 53-5a illustrates alternate ways to transition fro a single lane exit rap to two lanes. The additional lane is usually provided for the inor oveent. 54 COLLECTOR - DISTRIBUTOR (C-D) ROADS 54.1 Use of C-D Roads The reason for using C-D Roads is to iniize weaving probles and reduce the nuber of conflict points (erging and diverging) on the ainline. C-D Roads ay be used within a single interchange, through two adjacent interchanges, or continuously through several interchanges Design of C-D Roads When a C-D Road is provided between interchanges, a iniu of two lanes should be used. Either one or two lanes ay be used on C-D Roads within a single interchange. The cross section eleents for one and two lane C-D Roads should be in accordance with the one lane and two lane directional roadways shown in Figure The design speed of a C-D Road should norally be the sae as the ainline design speed but ay be reduced by not ore than 1 ph. The separation between the ainline and C-D Road paveents should be designed to prevent, or at least discourage, indiscriinate crossovers. As a iniu, the separation should be wide enough to provide noral shoulder widths for both the ainline and C-D Road roadways plus a suitable edian. Norally, a standard concrete barrier edian is used since C-D Road separation often involves obstructions such as bridge parapets, piers or overhead sign supports. There ay be isolated cases where a lesser type edian ay be used C-D Road Entrance and Exit Terinals Figure 54-1 shows both Low-Speed and High-Speed C-D Road entrance terinals. Three exit terinal lane conditions are shown on Figure These terinal designs are to be applied to highways using High-Speed exit terinals. Superelevation at C-D Terinals shall be developed siilar to that described in Section January

24 5 Interchange Design 55 MULTI-LANE RAMP & ROADWAY TERMINALS AND TRANSITIONS When two roadways converge or diverge, the less significant roadway should exit or enter on the right. Left-hand exits or entrances are contrary to driver expectancy and should be avoided wherever possible Multi-lane Entrance Raps and Converging Roadways General Figure 55-1a shows the design to be used for ulti-lane entrance raps and converging roadways. Converging roadways are defined as separate and nearly parallel roadways or raps which cobine into a single continuous roadway or rap having a greater nuber of lanes beyond the nose than the nuber of lanes on either approach roadway. (Single-Lane Entrance Terinals should be used in lieu of Converging Roadway drawings when a speed change lane is required.) Figure 55-1b shows the specific design to be used for two-lane High-Speed entrance raps. High-Speed Converging Roadways should be used when either or both of the Converging Roadways are ainline roadways of an expressway or freeway or if the design speed of converging directional raps is 5 ph or higher. Low-Speed Converging Roadways should be used at the convergence of directional raps within an interchange or at the convergence of interchange raps with non-liited access roads or streets where design speeds are 45 ph or lower Lane Balance and Continuity In order to avoid inside erges, the nuber of ainline lanes plus converging lanes approaching the nose ust be equal to the resultant nuber of lanes leaving the nose. To ake this possible, it is often necessary to carry additional ainline lanes past the nose for an adequate distance prior to tapering back to the desired nuber of lanes. These details are shown in Figure 55-1a Inside Merges When using a taper type of ultilane entrance rap an inside erge is created with traffic traveling on both sides of the erging lanes. If either vehicle involved with the erging oveent abandons the erge, traffic in the adjacent lanes could prevent the erging vehicles fro escaping to the adjacent lanes. By contrast, the parallel type ultilane entrance rap, as shown in Figure 55-1a, allows the erging vehicle to escape to the right shoulder without any interference. For the above reasons, inside erges are not desirable Preferential Flow On Figure 55-1a, one roadway in each design is labeled PREFERENTIAL FLOW. This indicates the ore iportant of the two approaching traffic flows. In selecting the preferential flow a designer ust consider the effect of traffic volues, nuber of lanes, sign route continuity and iportance, vehicle speeds and roadway alignent. Lanes carrying the preferential flow are given the higher design January

25 5 Interchange Design treatent. When it is necessary to reduce a nuber of converging lanes or where an angular change in direction ust occur, the design should favor the preferential flow Horizontal Curvature Horizontal curves of roadways approaching the terinal nose should confor to ainline roadway criteria in the case of ainline roadways and to rap entrance terinal criteria in the case of raps Crest Vertical Curves Crest vertical curves on constant-width roadways approaching the erging nose should be designed to provide sight distance consistent with the design speed of the roadway. Crest vertical curves fro the erging nose forward to a point where paveent convergence ceases and to the converging portion of an approaching roadway where the nuber of lanes is being reduced in advance of the nose should be designed using the decision stopping sight distance shown in Figure (See Figure 55-1a.) When it is not feasible to provide decision stopping sight distance, at a iniu, 125% SSD (Figure 21-1) should be provided. When design speeds differ on approaching roadways, the higher of the two design speeds shall be used in designing the crest vertical curve beyond the erging nose Superelevation and Joint Location Reference shall be ade to Section for superelevation requireents. Longitudinal joints should be located so they will coincide with and define the lane lines. Reference should be ade to Standard Construction Drawing BP-6.1 for type and location Multi-lane Exit Raps and Diverging Roadways General Figure 55-2a shows the general design for ulti-lane exit raps and diverging roadways. A diverging roadway is defined as a single roadway which branches or forks into two separate roadways without the need of a speed change lane. Figure 55-2b shows the specific designs to be used for a two-lane high-speed exit rap at a syste interchange or the exit fro the ainline of a two-lane CD-Road. Figure 55-2c shows exaples of designs for diverging roadways. Figure 55-2d shows the specific designs to be used for a two-lane high-speed exit rap at a service interchange. Type I should norally be used. Type II should only be used when queuing in the optional lane does not extend to the physical gore (long raps, Parclo B, etc.). High-Speed Diverging Roadways should be used when either or both the diverging roadways are ainline roadways of an expressway or freeway or at the divergence of high-speed directional raps within an January

26 5 Interchange Design interchange. Low-Speed Diverging Roadways should be used at the divergence of low-speed directional raps within an interchange or at the divergence of raps with non-liited access roads or streets Lane Balance and Continuity In order to have lane continuity, the nuber of ainline lanes leaving the diverging nose ust be equal to the nuber of ainline lanes approaching the nose. The total nuber of lanes leaving the diverging nose (ainline lanes plus diverging lanes) ust be one greater than the total nuber of lanes approaching the nose to obtain lane balance. The purpose for obtaining lane continuity and lane balance is to avoid a drop lane situation. See Figures 55-2a and 55-2b. It ay be necessary to obtain this lane balance by adding additional lanes upstrea fro the diverging nose. The length of each additional lane should be 2,5 ft. and should be introduced using a to 12 ft. taper with a length of 1 ft. as shown on Figure 55-2b for the approach roadway class and design speed. There ay be conditions off the ainline, such as on Collector-Distributor Roads or within interchanges, where lane balance and continuity is less iportant. In such cases, the non-ainline roadway design on Figures 55-2a and 55-2b ay be used Terinal Design The design of diverging roadway terinals is deterined by the class and the design speed of the approach roadway, and is based on the neutral gore length "L" and the nose width "N" (See Figure 55-2a). Table A on Figure 55-2a lists length "L" and nose width "N" for various design speeds in diverging roadway classes. The "N" diension should be exact, but the "L" diensions ay vary slightly fro the Table A value Horizontal Curvature Table B on Figure 55-2a lists recoended values for the curve differential between the outer edges of traveled way of diverging roadways. These values apply only when the alignent between the diverging nose and the PC of the diverging curvature is on tangent or siple curvature. When copounded or spiral curvature is used in the diverging area, it will be necessary to design diverging roadway alignents individually to provide the proper "L" and "N" for the approach roadway Class and design speed Crest Vertical Curves When a diverging nose is located on a crest vertical curve, this vertical curve shall be designed using the design speed of the approach highway and decision stopping sight distance fro Figure When it is not feasible to provide decision stopping sight distance, at a iniu, 125% SSD (Figure 21-1) should be provided. January

27 5 Interchange Design Superelevation and Joint Location The superelevation rate will be based on the design speed of the approach roadway. Reference should be ade to Section for other superelevation requireents. Longitudinal joints should be located so they will define the lane lines. Reference should be ade to Standard Construction Drawing BP-6.1 for type and location. The joints in the gore area should be located to facilitate superelevation and paveent grading Four Lane Divided to Two Lane Transition Figure 55-3 shows a reversed curve design (Types A and B) a tapered design (Type C) and a design for a transition on a curve (Type D). The paveent transition should be located in an area where it can easily be seen. Intersections or drives should be avoided in the transition area. Vertical or horizontal curves should provide decision stopping sight distance. Reverse curve transitions should norally be used for edian widths of 2 ft. or wider. Taper lengths are calculated as shown in Section SERVICE ROADS 56.1 Use of Service Roads Service roads (frontage roads) are used to enhance capacity on the ainline, control access, serve adjacent properties, or aintain traffic circulation. They perit developent of adjacent properties while preserving the through character of the ainline roadway. Service roads ay be either one-way or two-way, depending on where they are located and the purpose they are intended to serve Design of Service Roads Although the alignent and profile of the ainline ay have an influence, service roads are generally designed to eet the specific criteria based on functional classification (usually "local"), traffic volues, terrain/locale and design speed. Two features, however, are unique to service roads and are further discussed below. They are (1) the separation between the service road and ainline and (2) the design of the crossroad connection. The further the service road is located fro the ainline, the less influence the two facilities will have on each other. A separation width that exceeds the clear zone easureent for each roadway is desirable. However, the separation should be at least wide enough to provide noral shoulder widths on each facility plus accoodate surface drainage and a suitable physical traffic barrier. Glare screen is desirable to screen headlights when the service road is two-way. January

28 5 Interchange Design At crossroads, the distance between the ainline and service road becoes extreely critical. This distance should be great enough to provide adequate storage on the approaches to both the ainline and service road. The recoended iniu distance between the ainline and service road edges of traveled way is 15 ft. in urban areas and 3 ft. in rural areas. In addition, the designer should check the adequacy of stopping sight distance on the crossroad as well as intersection sight distance at the frontage road. Since service roads are norally aintained by local governental agencies, the paveent design should either eet, or exceed, that required by the aintaining agency. 55 REQUESTS FOR NEW OR REVISED ACCESS INTERSTATE HIGHWAYS OR OTHER FREEWAYS 55.1 General Control of access on the Interstate and other freeway systes is considered critical to providing the highest quality of service in ters of safety and obility. This section provides guidance for the preparation and processing of access point requests in relation to new and existing interchanges on the Interstate and other freeway systes in accordance to Federal Code 23 U.S.C. 111 and FHWA s Policy on Access to the Interstate Syste, dated May 22, 217. The docuentation required depends on the type of change requested - new or revised. New Access is the addition of a point of access where none previously existed. This includes the construction of an entirely new interchange such that it will result in additional points of access or additional raps to existing interchanges. As an exaple, the reconstruction of an existing diaond interchange to a full cloverleaf interchange would add four new points of access. Revised Access is the ajor revision of an existing interchange such that the nuber of access points will reain the sae but the operation and/or safety of the Interstate/freeway syste ay be affected. The changing of a cloverleaf interchange to a fully directional interchange, the conversion of a traditional diaond to a diverging diaond interchange, relocating an existing rap to terinal to a new roadway, and adding a collector-distributor syste are all considered exaples of revised points of access. New or revised access point requests require the preparation and processing of an Access Point Request Docuent. Generally, a new access requires an Interchange Justification Study (IJS), and a revised access requires an Interchange Modification Study (IMS) Interchange Study (Access Point Request Docuent) The degree of coplexity of the Interchange Study will vary depending on the character of the location (urban or rural) and/or whether the change involves a revised access point, a new access point at an existing interchange, or an entirely new interchange location. To coincide with FHWA s Policy on Access to the Interstate Syste, the following is a list of ites which ust be addressed in the interchange study for a new or revised access on the Interstate/freeway syste: January

29 5 Interchange Design 1. Evidence that the proposed new or revised access does not have significant adverse ipact on the safety and operation of the Interstate/freeway syste. The analysis ust address design year traffic with and without the new or revised access point (build vs. no-build). Design year traffic ust reflect future land use changes and associated trip generations. Traffic projections ust be certified as per Section Requests involving new access points or revised access points ust use 2 year design traffic projected fro the opening day of the interchange. The level-of-service (LOS) of the Interstate/freeway syste and the interchange coponents that are built new or odified should generally provide a LOS C, except certain cases in the MPO s Boundary where LOS D ay be acceptable. The proposed Interstate/freeway interchange or iproveents cannot have a significant adverse ipact on the safety and operation of the Interstate/freeway facility based on an analysis of design year traffic. A significant ipact occurs when the Build Condition degrades traffic operations, see Section to deterine if degradation occurs. The operational analysis shall, particularly in urban areas, include an analysis of sections of Interstate/freeway to and including at least the first adjacent existing or proposed upstrea and downstrea interchange. Crossroads and other roads and streets shall be included in the analysis to the extent necessary to assure their ability to collect and distribute traffic to and fro the interchange with new or revised access points. New interchanges ust include analysis of the local street syste to the extent that local road syste iproveents can be copared as an alternative to constructing a new interchange. Maps and/or diagras should be provided as needed to clearly describe the location and study liits of the proposal. For requests involving entirely new interchanges, the study should include a discussion of the distance to, and size of, counities to be served by the new interchange. An exaination of proper interchange spacing ust also be included. Every IMS/IJS should include a conceptual signing plan showing the type and location of signs to support the proposed design. 2. Assurance that the new or revised access connects to a public road and is part of a configuration that provides for all traffic oveents. Less than full interchanges for special purpose access for transit vehicles, for HOV s, or into park and ride lots ay be considered on a case-by-case basis. Proposed design ust eet or exceed current design standards. In rare instances where all basic oveents are not provided by the proposed design, the report ust include a full-interchange option with a coparison of the operational and safety analyses to the partial-interchange option. The report ust also include the itigation proposed to copensate for the issing oveents, including wayfinding signage, ipacts on local intersections, itigation of driver expectation leading to wrong-way oveents on raps, etc. The report ust describe whether future provision of a full interchange is precluded by the proposed design. The developent of an Access Point Request Docuent should be perfored in accordance with the ODOT Project Developent Process (PDP). As part of the PDP for all projects that require an IJS/IMS, January

30 5 Interchange Design the relevant PDP subissions (including, but not liited to the Feasibility Study and Alternative Evaluation Report), will include consideration of the following points: 1. Adequate docuentation that the existing access points and/or local roads are unable to handle the design year traffic deands while providing the access intended by the proposal, or be iproved to do so, if the new or revised access is not provided. If the request involves a new access point, and particularly an interchange at a new location, a coprehensive description of the public need for the access ust be included. A justification based on enhanced property values or access to private facilities will not be accepted. 2. Assurance that all reasonable alternatives for design options, location, and transportation syste anageent type iproveents (such as rap etering, ass transit, and HOV facilities) have been assessed and provided for if currently justified, or provisions are included for accoodating such facilities if a future need is identified. 3. The proposal considers and is consistent with local and regional land use and transportation plans. Prior to final approval, all requests for new or revised access ust be consistent with the etropolitan and/or statewide transportation plan, as appropriate, the applicable provisions of 23 CFR part 45 and the transportation confority requireents of 4 CFR parts 51 and 93. The request should include a stateent and analysis of copatibility with, and the effect on, the local road network. Letters of support and coitent are required fro the State and other sponsoring agencies for any required street or road iproveents as well as for the access point. 4. In areas where the potential exists for future ultiple interchange additions, all requests for new or revised access are supported by a coprehensive Interstate/freeway network study with recoendations that address all proposed and desired access within the context of a long-ter plan. 5. Evidence that the request for the new or revised access generated by new or expanded developent deonstrates appropriate coordination between the developent and the necessary transportation iproveents. A discussion of potential funding sources, if known, should be included. 6. The request for new or revised access contains inforation relative to the planning requireents and the status of the environental processing of the proposal. As part of ODOT s Project Developent Process, the Office of Roadway Engineering is required to review and approve all Feasibility Studies and Alternative Evaluation Reports involving an Interchange Study (IJS/IMS/IOS). If the FS and/or AER involves an interchange, the study liits ust encopass the applicable interchange study (IJS/IMS/IOS) liits. The Office of Roadway Engineering will not review any Interchange Study (IJS/IMS/IOS) that: 1. Does not have an approved Purpose & Need (if applicable); or 2. Does not have appropriate study liits required to support the approved Purpose & Need; or 3. Has interchanges that ORE did not review and approve in the Feasibility Study and Alternative Evaluation Report (if applicable) January

31 5 Interchange Design The Access Point Request Docuent should only be perfored for the preferred alternative, however a discussion of feasible alternatives should also be included in the study. The preferred alternative will coply to all State and FHWA design requireents, including but not liited to: interchange spacing, interchanges to provide for all traffic oveents to and fro the freeway, not allowing lanes to drop into private facilities, not allowing intersections (driveways or streets) to intersect raps (except in special cases such as facilities for utilities Interchange Modification and Justification Studies (IMS & IJS) are required to reference and describe how each policy point in FHWA s Policy on Access to the Interstate Syste is being et (link to latest policy: All IJS or IMS docuents should follow the Report Forat/Outline found in the Traffic Acadey Interchange Studies (IJS/IMS/IOS) Course Manual. The Interchange Studies Course Manual can be found on the following website: A reevaluation of the IJS/IMS ay be required by FHWA if the project or a phase of the project has not been constructed within 3 years of the approval date of the docuent. An IJS/IMS Addendu is required if any of the following condition(s) apply: 1. A Revised-Build condition is proposed that is different than the Build condition (per the approved IJS/IMS) and is not an Interi-Build condition (a phased condition between the No-Build condition and Build condition, per the approved IJS/IMS). See Section if your project does not eet the condition(s) listed above. Contact The Office of Roadway Engineering Interchange Operations Study (IOS) Many inor interchange projects, especially those involving service interchanges, do not fall under the definition of warranting an Access Point Request Docuent (IJS/IMS) per the FHWA s Policy on Access to the Interstate Syste, but still require an operational evaluation and approval by the Office of Roadway Engineering. This operational evaluation would be in the for of a report referred to as the Interchange Operations Study, IOS. The IOS is intended to be an abbreviated version of the ore coprehensive IMS report, highlighting critical traffic operations that ay be affected by the proposed iproveent. The IOS will utilize the sae analysis ethodology and 2 yr. design as the IMS, but the IOS will be ore liited with respect to the nuber of analysis points evaluated and the study narrative. An IOS can be applied to an Interstate or non-interstate. The following is a list of projects requiring an IOS: 1. Changing lane configurations at a rap intersection approach, including: Adding/reoving a left, thru, or right turn lane along a crossroad Adding/reoving turn lanes to the exit rap Changing lane assignents without altering the nuber of lanes a. Exaple: Changing a 2 lane approach fro a (Left/Thru-Right) to (Left- Thru/Right) Ipleenting a Road Diet (reducing the nuber of lanes on the crossroad) Squaring up a continuous right turn fro the rap/crossroad and regulating the oveent with a signal January

32 5 Interchange Design Converting a squared right turn to/fro rap/crossroad to a slip rap 2. Changing the exit or entrance rap terinus point with the freeway ainline by: Creating an optional exit lane Creating a 2-lane exit Creating a 2-lane entrance 3. Shifting a rap s location within the sae interchange configuration 4. Changing traffic control type at a rap/crossroad intersection fro a signalized/unsignalized condition to a roundabout 5. Adding an auxiliary lane between 2 adjacent rap interchange raps An IOS cannot be considered for: A) Major interchange design/revisions; B) New interchanges; or C) Interchange odifications necessitated by large developents or conditions that will significantly increase traffic volues or revise traffic patterns. For all other interchange or ainline odifications that result in significant operational changes, not covered above or by an Interchange Modification Study, please contact the Office of Roadway Engineering. An IOS is required in cases where an Interi-Build condition (a phased condition between the No-Build condition and Build condition, per the approved IJS or IMS) is proposed. For these cases the Office of Roadway Engineering ust agree with the design year and traffic volues used for analyses. The IOS ust state and address the following questions: 1. Does the Interi-Build condition build toward the Full-Build condition (per the approved IJS/IMS)? 2. Does the Interi-Build condition provide benefit copared to the No-Build condition (per the approved IJS/IMS)? 3. Does the Interi-Build condition preclude construction of the Full-Build condition (per the approved IJS/IMS)? 4. Is the Full-Build (per the approved IJS/IMS) design still valid? A reevaluation of the IOS ay be required by ODOT if the project or a phase of the project has not been constructed within 3 years of the approval date of the docuent Safety Iproveents on Interstate or Other Freeways Safety iproveents eligible for this process are defined as low to ediu cost solutions that address an identified spot safety proble. The LOS provisions of Section 55.2 do not apply except that the LOS should not be degraded over the no-build condition in the design year. All other provisions of 55.2 still apply, including the IMS or IOS report to support the analyses. To deterine degradation, the individual operational coponents shall be analyzed, but evaluated for acceptance within the context of the overall affected syste. Though a single operational coponent could experience increental degradation, the overall syste should iprove or essentially reain the sae. For a safety iproveent to qualify under this section, the following criteria ust be et: 1. The project purpose and need is priarily to address spot safety probles. The purpose and need ay not include operational perforance or econoic developent objectives. 2. The location has separate independent utility fro all other iproveents 3. Any potential longer ter solution which would provide LOS C would take 5 or ore years to ipleent. January

33 5 Interchange Design 4. No ajor rehabilitation or reconstruction is planned for 5 or ore years. Other work (e.g., routine aintenance or inor rehabilitation) ay be done within the 5 year window as long as it does not substantially replace the base paveent and/or reconfigure the facility. 5. The location is a spot location (defined as a rap, intersection, erge/diverge point, weave, or ainline section not to exceed one ile). 6. The location planning level cost estiate is less than $5 illion total (low to ediu cost easures) for all phases of project developent (i.e. preliinary engineering, detail design, right of way and construction) Study Methodology General One of the priary objectives of an Interchange Study is to deterine if additional traffic enters the Interstate/freeway in the build versus the no-build case, and if traffic does increase, does it degrade the operation of the Interstate/freeway. In cases of new interchanges or new access points, the new roadway and connections will generally result in changed traffic patterns fro the no-build case. In the case of revised access projects, the build and no-build traffic volues ay be identical. In these cases, it is iportant to understand the concept of constrained traffic. Another priary objective is to ensure vehicles exiting the Interstate/freeway do not negatively ipact vehicles reaining on the Interstate/freeway. Providing adequate storage for the off-rap and optiizing signal progression away fro a service interchange are two ways this is accoplished Constrained Traffic In any cases, the purpose of a project is to alleviate traffic congestion at an interchange, possibly due to over saturated rap terinal intersections or inadequate rap capacity. In these cases, the proposed solution generally includes capacity iproveents such as turn lanes and/or additional through lanes intended to reove the geoetric constraint, or bottleneck. In order to deterine the effect of the proposed iproveent on the Interstate/freeway, traffic analysis tools such as the Highway Capacity Manual (HCM) or Highway Capacity Software (HCS) ust be used. The following steps are needed to deterine if degradation occurs when coparing the No-Build condition to the Build condition: 1) Referencing the table below, deterine if degradation ay be occurring by coparing the HCS level of service (LOS) for the No-Build and Build conditions downstrea of the on-rap at a) the erge and downstrea freeway segent, or b) the weave. January

34 5 Interchange Design LOS Is there Degradation? No-Build Build Urban/ Suburban Rural A, B, C A, B, C No No C D No Check D E D No Check E Check Check E Check Check F Check Check F F Check Check 2) If No degradation occurs then nothing else required. If Check then prepare/calculate constrained analyses, see Traffic Acadey Interchange Studies (IJS/IMS/IOS) Course Manual and Exaple Proble ) Intersections are to be analyzed per Section 41.2 and Figure 41-14a, using design-year traffic, for both the AM peak hour and PM peak hour, or idday peak hour, if applicable. Degradation occurs when the Build traffic volue is greater than or equal to 2.% of the No-Build traffic volue, see Exaple Proble ) If the constrained analyses result in a traffic volue increase greater than 2 percent, the project will not be peritted unless itigative easures are included to either restrain vehicles fro entering the freeway (i.e., rap etering, geoetric constraints), or additional capacity is provided on the freeway to restore the LOS. ODOT and FHWA will decide what itigative easures, if any, will be allowed. 5) For over saturated oveents, the deand volue should be divided by the volue-to-capacity (V/C) ratio of that oveent to deterine the actual, or constrained, flow volues to be used in the downstrea erge and ainline, or weave LOS calculations. The difference between the no-build constrained traffic flow and the build (typically unconstrained, or less constrained) traffic flow is the increase of traffic volue entering the Interstate/freeway Diagras and Plans The Access Point Request Docuent should contain diagras and plans as needed (as applicable) to indicate: project liits, adjacent interchanges, proposed interchange configuration, travel lanes and shoulder widths, raps to be added, raps to be reoved, rap radii, rap grades, acceleration lane lengths, deceleration lane lengths, taper lengths, auxiliary lane lengths, and collector/distributor roads. January

35 5 Interchange Design 55.4 Subission of Interchange Studies All request subissions are to be sent to the Office of Roadway Engineering (electronic copy) with two printed copies to the ODOT District Office. The Office of Roadway Engineering will be responsible for coordination with the Federal Highway Adinistration for studies involving Interstates. All traffic analysis files ust be subitted (HCS, Synchro, SIDRA, etc.) 55.5 Review of Interchange Studies For Interstates, the Office of Roadway Engineering will review and approve the Access Point Request Docuent (IJS or IMS), and if acceptable, will forward the request to FHWA for their approval. If the environental docuent has not been copleted, approval will be conditional on acceptance of the environental docuent. For Access Point Request Docuents (IJS or IMS) involving non-interstate freeways, the Office of Roadway Engineering will review the study and has approval authority. For Interchange Operations Studies, the Office of Roadway Engineering will review and has approval authority. As a courtesy, all IOS subissions involving the Interstate will be ade available electronically to FHWA. January

36 5 Interchange Design LIST OF FIGURES Figure Date Title /213 Rap Design Speed Guide 53-1a 7/212 Miniu Rap terinal Spacing 53-2a 7/213 Miniu Acceleration Lengths for High-Speed Entrance Terinals with Flat Grades of 2% or Less 53-2b 7/213 High-Speed Entrance terinal Adjustent Factors as a Function of Grade 53-2c 7/212 High-Speed Single-Lane Entrance Terinal 53-3a 7/213 Miniu Deceleration Lengths for High-Speed Exit Terinals with Flat Grades of 2% or Less 53-3b 1/24 High-Speed Exit Terinal Adjustent Factors as a Function of Grade 53-3c 7/213 High-Speed Single-Lane Exit Terinal 53-4a 7/218 Low-Speed Entrance Terinals 53-4b 7/218 Low-Speed Exit Terinals 7/218 Notes for Low-Speed Entrance and Exit Terinals /218 Uncurbed Rap Intersection 53-5a 1/24 Transition Fro Single Lane to Two-Lane Exit Rap /25 Collector-Distributor Entrance Terinals /24 Collector-Distributor Exit Terinals 55-1a 7/218 Multi-Lane Entrance Raps and Converging Roadways 55-1b 7/218 High-Speed Two-Lane Entrance Terinals 55-2a 1/215 Multi-Lane Exit Raps and Diverging Roadways 55-2b 7/218 High-Speed Two-Lane Exit Terinals for Syste Interchanges 55-2c 1/24 Exaples of Diverging Roadways 55-2d 7/218 High-Speed Two-Lane Exit Terinals for Service Interchanges /26 Transitions - Four Lane Divided Roadway to Two Lane Roadways January

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38 RAMP DESIGN SPEED GUIDE 53-1 REFERENCE SECTIONS 53.2 RAMP MAINLINE DESIGN SPEED <ph) DESIGN SPEED <ph) UPPER RANGE MIDDLE RANGE LOWER RANGE Note: Rap design speeds do not pertain to the rap terinals.

39 TYPICAL GORE AREA CHARACTERISTICS -I :a s:: s:: - _z z- l> s:: r c: s::.,, :a l> l> -.,, s: z C) ::J:J,, 1 ::J:J (Tl z (,J (Tl I... w (h -t z (h Q) - July 212 ENTRANCE-ENTRANCE OR EXIT-ENTRANCE TURNING ROADWAYS ENTRANCE-EXIT (WEAVING) EXIT-EXIT ii ii LJ Ll FULL FREEWAY [J 7(- II * NOT APPLICABLE TO CLOVERLEAF LOOP RAMPS SYSTEM TO SERVICE TO CDR CDR SYSTEM SERVICE SERVICE SERVICE FULL OR OR INTER- INTER- INTERCHANGE INTERCHANGE FREEWAY FDR FDR CHANGE CHANGE FULL CDR OR FULL CDR OR FWY. FDR FWY. FDR MINIMUM LENGTHS MEASURED BETWEEN SUCCESSIVE RAMP TERMINALS 1 ft 8 ft 5 ft 4 ft 8 ft 6 ft 2ft 16 ft 16 ft 1 ft NOTES: CDR - COLLECTOR DISTRIBUTOR ROAD FDR - FREEWAY DISTRIBUTOR ROAD The recoendations are based on operational experience and need for flexibility and adequate signing. They should be checked in accordance with the procedure outlined in the Highway Capacity Manual (HCM). Also refer to the HCM for the procedure for easuring the length of the weaving section. The "L" distances noted in the figures above are easured between the painted noses (theoretical gore point). Additionally for EN-EN, a iniu distance of 3 ft. is recoended between the end of the taper for the first entrance rap and the painted nose for the succeeding entrance rap (siilar for EX-EX except use the physical nose). Painted Nose (Theoretical Gore Point) Marked Gore Area (Neutral Area) Physical Gore Area Physical Nose -=--

40 MINIMUM ACCELERATION LENGTHS 53- FOR HIGH-SPEED ENTRANCE TERMINALS REFERENCE WITH FLAT GRADES OF 2!. OR LESS a SECTION Mainline Acceleration length, L tftj for design Design Speed, speed of lost rop curve, Vr V fphj tphj Stop BIO / / Moinlt'ne Design Speed <VJ \\A Lost Rop Curve Design Speed <VrJ == 5:I Toper Acceleration Length, L <ftj 12' ==,u The Acceleration Length, L, Sholl Be Adjusted For Grode With Figure 53-2b.

41 HIGH-SPEED ENTRANCE TERMINAL ADJUSTMENT FACTORS AS A FUNCTION OF GRADE 53-2b REFERENCE SECTION Mainline Design Speed tphj Ratio of length on grade to length on level for design speed of lost rop curve fphj to 4% upgrade 5 I.JO All Speeds 3 To 4% downarade I.BO 5 to 6% upgrade I.BO to 6% downarade No adjustent required for grades less than 3%. Ratio fro this table ultiplied by acceleration length in Figure 53-2 gives acceleration length on grade. The grade "' in the table is the average grade easured over the distance for which the acceleration length applies.

42 Mainline Design Speed, V (ph) =============== - *** 12 1 I -1 L ::c- C> z ::c I -I ::a (J) )>i "'tj z o e -I Z ::a C) :s::r - Z )>i r- r- )>i z - :a I "Tl CJ1 ::r, c.r, "-" w o, N I\.) (") o I. I _J I 23' 25' 25' (Entrance Nose) 5:1 Shoulder Taper Last Rap Curve Design Speed, Vr (ph) Ls*, 2' Lp_ Lt= 65' Min. Spiral (Parallel Length} (Length On Taper) Acceleration Length, L (Figure 53-2a) Adjusted To Grade (Figure 53-2b) 125' - 5:1 Taper 6' * Length May Be Increased For Superelevation Transition ** To Deterine Lp, Subtract Ls And Lt Fro L. *** Mainline paved shoulder width as required by Figure 31-3 or July 212 Notes For Single Lane Entrance Terinals 1. The iniu acceleration length, L, shall be Ls + Lt. 2. The 9' to 23' variable width of treated shoulder of the entrance terinal shall be sloped for 12' as required for ainline design (usually ½in./ft.), except for the last 1' to 2' at the 9' end, which is to be sloped as required for proper terinal grading. 3. Norally single lane raps will have a width of 16'. The width shall be increased to 18' when the rap radius is less than 2'. When an 18' wide rap is used, the 25' entrance terinal width shall be retained and the 9' width reduced by 2'. 4. If Lp (parallel length) is not required (L <= 85'), then the 2' iniu spiral should be tangent to the 5:1 taper. 5. If the entrance terinal results in an add-lane (no erge), delete the last 6' of the 5:1 taper

43

44 HIGH-SPEED EXIT TERMINAL ADJUSTMENT FACTORS AS A FUNCTION OF GRADE 53-3b REFERENCE SECTION Mainline Design Speed (ph) Ratio of length on grade to length on level for design speed of first rop curve (phj All Speeds All Speeds 3 to 4% upgrade 3 to 4% downgrade All Speeds to 6% upgrade 5 to 6% downgrade All Speeds No adjustent required for grades less than 3%. Ratio fro this table ultiplied by deceleration length in Figure 53-3 gives deceleration length on grade. The "grade" in the table is the average grade easured over the distance for which the deceleration length applies. October 24

45 I -1 ::c - G) ::c >< (J) - "'tj -I -I C :::c (J) :s::z L z G) l> r r- I r- l> z - :a I "Tl CJ1 ::r, QI "-" wi o, <,) w (") o I. I _J July 213 = , :/ Shoulder Toper Mainline Design Speed, V rphl _ ' Shoulder Toper s Li Extt Curve See Note IJ P.C.C. Or Mid-Point of 2' Spiro/ u Or Other Design Speed Liiting Geoetric Control Such As The Stopping Sight Distance For A Vertical Curve Or The Bock Of A Traffic Queue. b. Mainline paved shoulder width as required by Figure 31-3 or Notes For High-Speed Single-Lone Exit Terinals Deceleration Length, L Figure 53-3I Adjusted To Grode ffiqure 53-3bJ Miniu Length = 8' EXIT CURVE TABLE Mainline MAXIMUM EXIT CURVATURE, De Design Speed ph Rural,._ 24',._ 35',._ 5' 2-1' 2-4' Urban -,._ 35',._ 55' 2 15' 2-45' 3-3' 23' 6' First Rop Curve Design Speed, vr rphl -- --{--- Treoted Shouldar GORE DETAIL I. The Exit Curve should norally be according to the Exit Curve Tobie where the ainline is on tangent. Where the ainline is on curving alignent, the axiu differential between the Exit Curve and the ainline curve should norally be the Exit Curve Tobie value. This differential, however, ay vary by as uch as one degree in order to ovoid o tangent exit alignent. rsee Section for the allowable transverse breaks in superelevotion cross-slope.i 2. When the First Rop Curve does not exceed 8, the Exit Curve ay be copounded directly with the First Rop Curve of o PCC 1' beyond the nose. When the First Rop Curve does exceed 8, o spiral should be placed between the Exit Curve and the First Rop Curve and the beginning of the spiral fcsj should be of the nose. 3. Norally single lone rops will hove o width of 16'. The width shall be increased to 18' when the rop radius is less than 2'. When on 18' wide rop is used, the 39' exit terinal width shall be retained and the 23' width reduced by 2'.

46 z -I ::a l> r- zo =e. en -I "tj ::a 31::c z l> r- en :ic, c.n :ic, u, z C') c.> en N C') --t z en I Q) Q) en z 4' See Detail 6' (See Note E-1) Mainline Treated Shoulder 6' 16' 3' July 218 6' 16' 3' 16' See Detail oc '?> (_ S ee Not e C-4) Q) en z TYPE A (See Note C-1) (See Note E-1) 4' I 12' 16' 35:1 Taper 7' - 35:1 Taper (See Note C-2) - 25: 1 Treated Shoulder Taper (See Note E-1).. }"aper Curb Height 6" to " in 1' 25:1 Treated Shoulder Taper 'fl Dc5 1- (See Note C-3) a.. CURBED ENTRANCE PAVED SHOULDER DETAIL (See Note E-2) TYPE B Cobined Acceleration-Deceleration Lane Shown (See Note C-1) LOW-SPEED ENTRANCE TERMINALS For Notes, see adjacent sheet.

47 -. -I >< -I :ei ::c en s: _ "tj z l> C r- en :ic, :ic, u, z C'). en W C') --t z en c.n w I er 6' 16' 3' ( S e O f e r. (J'<) () a.. 6' 42' - 35:1 Taper 25:1 Treated Shoulder Taper (See Note E-1) Mainline Treated Shoulder 6 1 S et 1 J_ I If July CURBED EXIT PAVED SHOULDER DETAIL OPTION 1 (See Note E-2) Mainline Shoulder, s (ft) TABLE A Nose Radius, R (ft) LOW-SPEED EXIT TERMINAL For Notes, see adjacent sheet. CURBED EXIT PAVED SHOULDER DETAIL OPTION 2 (See Note E-2)

48 5 Interchange Design Notes for Low-Speed Entrance and Exit Terinals Figures 53-4a and 53-4b A. GENERAL 1. Low-Speed Terinals are intended for used on highways which have little or no access control except through an interchange area. Many of the features of Low-Speed Terinals are applicable to a terinal of one rap with another rap in a freeway interchange. B. EXIT TERMINAL 1. The curve differential between the through roadway and exit curve D C1 ay vary fro a iniu of 4 to the axiu of Exit Curve D C1 ay be copounded or spiraled into Rap Curve D C2. If D C2 is greater than 25 then provide a 15 ft. spiral between D C1 and D C2. C. ENTRANCE TERMINAL: TYPE A & TYPE B 1. Type A is preferred and shall norally be used. However, when a rap enters as an added lane or as a cobined acceleration-deceleration lane, Type B ay be used if its use would result in a substantial savings in cost (i.e. reduced bridge width). 2. The acceleration lane of Type A shall be a unifor 35:1 taper relative to the through for either tangent or curving alignent. 3. The curve differential between the through roadway and entrance curve D C5 of Type B shall be The design of the entrance terinal curvature shall be based on the following: (a) Rap Curve D C3 of 8 or less When the through roadway tangent or a curve to the right, D C4 shall be a 15 ft. long siple curve of a degree such that the differential between it and the through roadway will not exceed 4. When the through roadway is on a curve to the left, a 15 ft. tangent shall be substituted for D C4. (b) Rap Curve D C3 greater than 8 A 15 ft. spiral ay be substituted for D C4. D. RAMP WIDTH 1. Norally single lane raps will have a width of 16 ft. The width shall be increased to 18 ft. when the rap radius is less than 2 ft. When an 18 ft. wide rap is used, the 35 ft. exit and 2 ft. entrance terinal widths shall be retained and the 19 ft. and 4 ft. widths reduced by 2 ft. E. TREATED SHOULDER 1. The treated shoulder along the speed change lanes shall be as shown on Figure If the rap or through roadway has a curb offset greater than 6 ft. (or 3 ft.), the greater width shall be used at the terinal. Retain the 19 ft. width. 3. The Special Detail drawings shall apply when the through roadway is curbed. July 212

49 C: -z Zo -I C: :JJ :JJ en e - -I :lj l> Z S::.,, :ic, "Tl :ic, z u, C') O (,) :... en C') --t z en U1 I U1 4' X 4' TAPER 16' _, SEE NOTE 2 6' R 4' X 4' TAPER t SEE NOTE 4 \ 4' X 4' TAPER 8' X 8' TAPER 25' R SEE 4' X 4' TAPER NOTE 2 N 6' R (SEE NOTE 1) 4' X 4' TAPER 5' R 5' X 5' TAPER 8' X 8' TAPER 8' July 218 5' R SEEINOTE 2 8' X 8' TAPER 5' R SEE NOTE 2 N 4' X 4' TAPER 6' R 4' X 4' TAPER NORMALLY RAMP CURVE SHOULD NOT OVERLAP INTERSECTION TAPER - 16' S.EE_NQTE. 3_ SEE 8' x 8' TAPER LL NOTE 2 LL 5' R t 5' X 5' TAPER NOTES: 1. WHEN THE ANGLE OF THE TURN INTO THE "ON" RAMP IS 1 OR GREATER, REDUCE THE 6' RADIUS TO 5'. 2. THESE POINTS SHOULD BE AT THE SAME CENTERLINE STATION OF THE CROSSROAD. 3. WHERE THE RAMPS INTERSECT A DIVIDED HIGHWAY, THE MEDIAN OPENING SHOULD BE DESIGNED TO DISCOURAGE IMPROPER TURNS INTO THE OFF RAMPS. 4. THE 25' RADIUS AND 1:1 TAPER MAY NEED TO BE SLIGHTLY ADJUSTED IF 5. THE ANGLE OF THE ON RAMP IS LESS THAN 9 (UTILIZING TURN TEMP LA TE SOFT ARE) ALL OF THE TURN MOVEMENTS AT THE INTERSECTION ARE TO BE ANALYZED WITH TURNING TEMPLATE SOFTWARE AND THE DESIGNATED DESIGN VEHICLE.

50 6' r- l> z -I :::D l> -I z o en- -I :::! =e oz I r- "'Tl zo l> :::D :s:::: >< en - - z -I C) r- :::D l> I :s:::.,, :a "Tl :a u, z u, C, w O c,.) I :...,. Ch u, C, -I z Ch C) IJ 16' C, - O" CP.., N.i=- Oecelerotion Lenoth, L ffioure 53-JoJ Adjusted To Grode (Figure 53-JbJ 12' ALTERNATE A ilz a zz; IJ :=: l"c =,,... t ---,,, 16,. I _ 1 r Oecelerotion Lenoth, L (Fioure 53-JoJ Adjusted To Grode (Figure 53-JbJ ALTERNATE B See Figure 41-9 and 41-1 to copute the length. The Miniu ecelerotion Length, L, After Adjustent For Grode (Figure 53-JbJ, Sholl Be 8' Note: The additional lone is usually provided for the inor oveent.

51 25' Zr -I :ti l> -I Zo :ti, C -I - en :ti -I s: - z C: l> -I o u, :ti :a :a z CTI f (,,) <.n I...Ii z <.n 8: I Taper 3 q r::mainlin; - Paveent - Edge I 1* 11 1 hl r8 ' f- 8:1 Taper Relative to Mainline _ ' T2'± 6'\ 5:l 7 7 f End C-D ** Separation Relative to 8: I T a_e_er I' I' - c.. t:» :::, C t:» N CTI High-Speed Entrance Ter ina I Criteria HIGH-SPEED COLLECTOR-DISTRIBUTOR ENTRANCE TERMINAL DESIGN SPEED>= 5 MPH 18' 6:1 Taper 11, f-l-=--::? ,i" oi,;; 1 i n -;, - Pov een t Edge 1 IO'r:} = =============== d,; =i.. I' 3', 2 16' 6' , 1l* 1 1,q - Nose Low-Speed Entrance Ter ina I Criteria Rel t_ive_ to_m _a,n _l,ne :.=-+-- Taper LOW-SPEED COLLECTOR-DISTRIBUTOR ENTRANCE TERMINAL DESIGN SPEED < 5 MPH ** * Use Shou Ider Widths fro either Figure 31-3 or Figure ** Use Sing le-lane Entrance Terinal Criteria, For 2 Or More Lanes Use Criteria

52 - I O 1 r- r ><, - -I -I -I J:J ffl J:J C =s:: - z -I J:J )> - r- en c: :o I -I J:J (11 u, g I (.) I\) l I _J * 24' 24 Exit Nose J =-= *** I I For Curvature See T ob le B Figure ' Min ANGENT** For Curvature See Tobie B Figure =--= '--- - = =- - I - - ' LANE EXIT FROM 4 LANES CT Cl) N.,:. * 24, Exit Nose - - For Curvature See Tobie B Figure 55-2 I 2' Min. TANGENT** J?4..L...---,1-12' *** 24' == For Curvature See Tobie B Figure 55-2 =r: LANE EXIT FROM 3 LANES -----= * 16' 24 Exit Nose For C ture See T ob le B, 2' ' M'... For Curvature See Tobie B - Figure 55-2 TANGENT** Figure 55-2 I TAPER I 16' I *** -- l == =:= LANE EXIT FROM 2 LANES * Distance to first rop exit nose 6' 1n1u with 1' desirable especially for two or ore lone C-D roods ** Or as required for superelevotion transitions *** Width deterined by type of C-D separation chosen IVV 1'

53 I I 35:: )> z C: C r- -I o7 r- z )> <z C> :::c - z z -I C) :::c )> :::c z C") l> C :e :::c )> )> -< 3:: en en.,, - :a "Tl :a c.n z cno c.n g I... en... Q) --t z en I, - July 218 ** * Design Taper Rate Speed L, 16 (ph) High-Speed Low-Speed Low-Speed = 4' r 5: : ', 36' or 48' ---- Preferential Flow : :1 -- TWO-LANE ROADWAY REDUCED TO SINGLE LANE PRIOR TO ENTRANCE NOSE 45 35: : :1 ** High-Speed= 9' Ll 16 Low-Speed = 4' f' 24', 36' or 48' High-Speed = 9' L * '\6' Preferential Flow * Lt 75 24', 36' or 48' High-Speed = 9', _ -1 Low-Speed - 4' 24', 36' or 48' TABLE A Preferential Flow SINGLE LANE CONVERGING WITH MUL Tl-LANE MUL Tl-LANE CONVERGING WITH MUL Tl-LANE * Note: the nuber of lanes leaving the entrance nose ust be equal to the total nuber of lanes (converging plus ainliine) approaching the entrance nose. ** See Figure 53-2c or 53-4a for terinal details. See Table A 2' See Table A 2' See Table A See Note A * I t 1- - DETAIL FOR DROPPING EACH CONVERGING LANE \ High-Speed = 9' Low-Speed = 4' NOTE A: Vertical alignent of both the ainline and the rap should provide Decision Sight Distance, Avoidance Maneuver C or E, as per Figure 21-6.

54 I' I : Zc, -I ::c :a J> en z "'C o C -I -I :e 3::o I Z r- J> J> r- z en ::ICI - "T1 en ::ICI z u, (") en O u, I :... en... (") C"' -I z en I I I Vertical alignent of both the ainline and the rap should provide Decision Sight Distance, Avoidance Maneuver C or E, as per Figure Note A-Additional lane provided to satisfy lane-balance. The Add-Lane ay be a basic lane if needed for capacity or an auxiliary lane and dropped either as shown below or at the next interchange. * Entrance Nose * Thru Lanes For Taper Rate, See ls Table A, Figure 55-1a Last Rap Curve Design Speed, Vr (ph) 2' 12' For Taper Rate, See Table A, Figure 55-1a TWO-LANE ENTRANCE TERMINAL WITH ADD-LANE Add-Lane or Auxilliary Lane (See Note A) * Thru Lanes For Taper Rate, See ls Table A, Figure 55-1a Last Rap Curve Design Speed, Vr (ph) 2' For Taper Rate, See 2' For Taper Rate, See Table A, Figure 55-1a Table A, Figure 55-1a TWO-LANE ENTRANCE TERMINAL WITH DROPPED AUXILLIARY LANE 12'

55 MUL Tl-LANE EXIT RAMPS AND DIVERGING ROADWAYS 55-2a REFERENCE SECTIONS 55.2 See Note A L l, 2' 12' /2' See Figure 55-2b for developent of lanes Diverg TYPICAL A TOTAL NUMBER OF LANES BEYOND THE NOSE EQUALS APPROACH LANES ing Curva ftl re, rab1, 99 See Note A L Dlverg g Curvature r,,., aufe 8 TYPICAL B TOTAL NUMBER OF LANES BEYOND THE NOSE EQUALS APPROACH LANES PLUS ONE TABLE 8 Desi gn TABLE A 't." "N". Desi gn Gore Length fft.j Nose Width ff t.j Speed of RECOMMENDED DIVERGING CURVA TUR (See Sec J DIVERGING CURVATURE Total Lones Beyond Divergi ng Nose Equals Hioh- ideed Low- Hiah-Soeed Low- Approoching Aooroacn Lones Al)DrOaeh Lones +I "V ph Urban!Speed Rural Urban Speed Roadway Hinh-' ;need Low- Hiah-Soeed Low 'V ph Rural Urban Speed 6. Rural Urban Speed 6. Rural o - 45' o - 45' o - 25' o - 25' ' 1 - ' o - 3' o ' 1-15' o - 35 ' o - 35' ' 1-3' o - 4' o - 4' ' 1-45' o - 45' o - 45' N diension includes 4' of a 16' lane ' 2 - ' 1 - ' 1 - ' ' 1-45' 4 5-3' 2-15' ' 2-45' ' 3-3' 1:,. Based on a Design Speed equal to f"v" - 1 phj Note A - Any lane cobination can be designed fro Table A and Typicals A and 8 by adding one or ore lanes to one or both sides of Typical A or adding one or ore lanes to both sides of Typical 8. Note 8 - When a 16 foot lane width is used after the diverging nose, the nose width "N" includes 4 feet of the 16 foot lane width. For two 16 foot lanes, "N" includes 4 feet of each lone. January 215

56 - =-- -.,, :a:, :::c - en C, -< :::c en )< -I - en -I -c s: -I _e z :a:, -I s: -I z =E :a:, l>, 1 :::c en r- l> l> z z C, en JJ "T1 CJ1 (J1 CJ1 (J1 I. I\) N u, -I z Thru Lanes Mainline Design Speed, V ph L - Gore Length Cl) 4 I Table A Figure 55-2a I z N - Nose Width Table A Figure 55-2a...; , l < i iu 1' 25' 1' 25' a. For Diverging Curvature See Table B Figure 55-2a July 218 Each additional diverging roadway lane ust be developed as shown TWO-LANE EXIT TERMINAL THE TOTAL NUMBER OF LANES BEYOND THE NOSE EQUALS THE NUMBER OF APPROACH LANES L - Gore Length Cl) 4 I Table A Figure 55-2a I z = = = = = = = = = = = = = = = =1 = = = = = = - -,; ' 25' i < i(.) a. For Diverging Curvature See Table B Figure 55-2a Each additional diverging roadway lane ust be developed as shown TWO-LANE EXIT TERMINAL THE TOTAL NUMBER OF LANES BEYOND THE NOSE EQUALS THE NUMBER OF APPROACH LANES PLUS ONE

57 EXAMPLES OF DIVERGING ROADWAYS 5O5-2c REFERENCE SECTIONS ' (24' -4' -4' = 16'} - Design Speed = 5 ph 16' J' 125':t De = 1 16' 6' High-Speed <Urban> - 1 Lane Rap to 1 Lane Left and 1 Lane Right The axiu differential between diverging curvatures should not exceed the volues in Tobie 8 of Figure Design Speed = 5 ph 4' - 2' 16' (24'-4'-4' = 16'} 16' 16' High-Speed <Urban> - 2 Lane Rap to 1 Lane Left and 1 Lane Right 32' Mainline Design Speed = 7 ph High-Speed <Rural> - 4 Lanes to 3-Lanes Left and 2-Lanes Right 1' 2' (24'-4' = 2'} 25':t 4' Design Speed = 6 ph De = o 4' High-Speed <Urban> - 2 Lane Rap or CD-Road to 2 Lanes Left and 1 Lane Right October 24

58 'Tl :c :::c - (J> C, :::c :c )< < - (J> - -I "tj --1 e - z :c -I s:: -I z =E :c l>, 1 :::c u, r l> l> z z C, (J> JJ "T1 CJ1 JJ <.n CJ1 <.n I. I\.) I\) u, -I z Thru Lanes 3l z Mainline Design Speed, V ph l < i iu 1' 15' 1' 15' a. For Diverging Curvature See Exit Curve Table of Figure 53-3c For Rap Developent See Figure 53-3c July 218 Each additional diverging roadway lane ust be developed as shown TYPEI TWO-LANE EXIT TERMINAL FOR USE ON ALL FACILITIES Thru Lanes THE TOTAL NUMBER OF LANES BEYOND THE NOSE EQUALS THE NUMBER OF APPROACH LANES 3l z = = = = = = = = = = = = = = = =1 = = = = = = =: ' 15' , (.) a. For Diverging Curvature See Table B Figure 55-2a For Rap Developent See Figure 53-3c Each additional diverging roadway lane ust be developed as shown TYPE II TWO-LANE EXIT TERMINAL LIMITED USE, SEE NOTE * THE TOTAL NUMBER OF LANES BEYOND THE NOSE EQUALS THE NUMBER OF APPROACH LANES PLUS ONE * Note: This type of exit terinal is discouraged in congested corridors. Traffic analysis operations ust show queuing of rap vehicles will be contained within the rap and not extend past the physical nose.

59 24' - I -1 "T1 -I C: ::D r- -I :e )> z ::u -I )> r- C )> - z z < Cl) c =i ::u o o z )> ::D Cl) co :e )> )> C -< :e )> -< lj I "T1 :a CJ'I u, z CJ'I u, I w en w - I ZI _J -- - Paint Stripe** -- = ' TYPE A - REVERSE CURVE Dc1 = 2 - ' or Less Dc2 = 2 - ' or Less a. July 218 _ L.aoe Red,otioaT,pec Leogth 24' _J 12' TYPE B - REVERSE CURVE Approach Taper *** Paint Stripe Shown Tapered Along Tangent =::: i 24' Notes: NOSE DETAIL Applies to all Types * See Figure 55-1a Table A for Miniu Lane Reduction Taper Rate. (I) - See Detail Lane Reduction Taper Length * I I I, i Placed Along Departure Taper Length Departure Taper Length *** 24' TYPE C - TAPERED ** Refer to OMUTCD for paint striping details. *** See Section to deterine Taper Length. TYPE D- ON CURVE

60 EXAMPLE PROBLEM Ex Constrained Traffic Volues Calculation Sheet for Deterination of Constrained Traffic Volues Exaple Exaple: Deterine whether construction of an additional eastbound left turn lane fro arterial to interstate would degrade the freeway operation. Step 1: How does the erge downstrea of the on-rap intersection operate? For this exaple, the erge for the No-Build and Build conditions operates at a LOS F for both, so there is potential degradation. Step 2: Prepare constrained analyses based on results of HCS intersection analyses. See next page for traffic volues and lane assignents. (Note: An iproveent is deeed to degrade the freeway operation if it increases traffic on freeway ainline by greater than 2.% when the freeway is operating at LOS F in the No-Build condition.) NO BUILD CONDITION Full deand eastbound left turn DHV onto freeway rap = 49 vph v/c is (fro HCS analysis), > 1. so constrained Capacity Constrained volue = vph/(v/c) = 49/1.329 = 369 vph Full deand westbound right turn DHV onto freeway rap = v/c is.613 (fro HCS analysis), < 1. so not constrained 39 vph Total volue entering freeway rap = constrained EBL +WBR = = 759 vph BUILD CONDITION Full deand eastbound left turn DHV onto freeway rap = 49 vph v/c is (fro HCS analysis), > 1. so constrained Capacity Constrained volue = vph/(v/c) = 49/1.136 = 431 vph Full deand westbound right turn DHV onto freeway rap = 39 vph v/c is.528 (fro HCS analysis), < 1. so not constrained Total volue entering freeway rap = constrained EBL +WBR = = 821 vph COMPARISON = 62 additional vehicles entering the freeway with the iproveent is constructed. % traffic added to freeway ainline due to iproveents = additional vehicles entering freeway after iproveents / (trips on ainline + No Build constrained vehicles entering fro rap) 62/( ) = 1.59 % ore traffic added to freeway due to iproveent 1.59% < 2. % Therefore, iproveent does not degrade freeway operation July 218

61 EXAMPLE PROBLEM Ex Constrained Traffic Volues July 218

62 EXAMPLE PROBLEM Ex Constrained Traffic Volues July 218

63 EXAMPLE PROBLEM Ex Constrained Traffic Volues July 218

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