Congestion Mitigation at IH 27 and U.S. Hwy 70 in Plainview, TX

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1 2010 Congestion Mitigation at IH 27 and U.S. Hwy 70 in Plainview, TX Hongchao Liu, Hao Xu, and Rhett Dollins Multidisciplinary Research in Transportation Texas Tech University Mulidisciplinary Research Center in Transportation April, 2010

2 Table of Contents List of Tables...3 List of Figures...5 Introduction...6 Project Objectives...8 Methodological Approach...13 Summary of Research Results and Recommendations...15 Alternative # Alternative # Alternative # Alternative # Summary and Recommendation

3 List of Tables Table 1: Existing s...15 Table 2: Existing Levels of Service West Side...15 Table 3: Existing Levels of Service East Side...15 Table 4: Alternative #1 Proposed s...16 Table 5: Alternative #1 Levels of Service West Side...16 Table 6: Alternative #1 Levels of Service East Side...17 Table 7: Alternative #1 Delay Values vs. Existing Delay Values (West Side)...18 Table 8: Alternative #1 Delay Values vs. Existing Delay Values (East Side)...19 Table 9: Alternative #2-1 Proposed s...20 Table 10: Alternative #2-1 Levels of Service West Side...20 Table 11: Alternative #2-1 Levels of Service East Side...20 Table 12: Alternative #2-1 Delay Values Vs. Existing Delay Values (West Side)...21 Table 13: Alternative #2-1 Delay Values Vs. Existing Delay Values (East Side)...22 Table 14: Alternative #2-2 Proposed s...23 Table 15: Alternative #2-2 Levels of Service West Side...23 Table 16: Alternative #2-2 Levels of Service East Side...23 Table 17: Alternative #2-2 Delay Values Vs. Existing Delay Values (West Side)...24 Table 18: Alternative #2-2 Delay Values Vs. Existing Delay Values (East Side)...25 Table 19: Alternative #3-1 Proposed s...27 Table 20: Alternative #3-1 Levels of Service West Side...27 Table 21: Alternative #3-1 Levels of Service East Side...28 Table 22: Alternative #3-1 Delay Values Vs. Existing Delay Values (West Side)...28 Table 23: Alternative #3-1 Delay Values Vs. Existing Delay Values (East Side)...29 Table 24: Alternative #3-2 Proposed s...30 Table 25: Alternative #3-2 Levels of Service West Side...30 Table 26: Alternative #3-2 Levels of Service East Side...30 Table 27: Alternative #3-2 Delay Values Vs. Existing Delay Values (West Side)...31 Table 28: Alternative #3-2 Delay Values Vs. Existing Delay Values (East Side)...32 Table 29: Alternative #3-3 Proposed s

4 Table 30: Alternative #3-3 Levels of Service West Side...33 Table 31: Alternative #3-3 Levels of Service East Side...33 Table 32: Alternative #3-3 Delay Values Vs. Existing Delay Values (West Side)...33 Table 33: Alternative #3-3 Delay Values Vs. Existing Delay Values (East Side)...34 Table 34: Alternative #4 Proposed s...36 Table 35: Alternative #4 Levels of Service West Side...37 Table 36: Alternative #4 Levels of Service West Side...37 Table 37: Alternative #4 Delay Values Vs. Existing Delay Values (West Side)...37 Table 38: Alternative #4 Delay Values Vs. Existing Delay Values (East Side)

5 List of Figures Figure 1: Site Overview...7 Figure 2: Existing Layout...9 Figure 3: Design Alternatives #2-1 and # Figure 4: Design Alternatives #3-1 and #3-2 (No Through/ Left Turn Option Lane)...11 Figure 5: Design Alternative #3-3 (Through/Left Turn Option Lane Allowed)...12 Figure 6: Design Alternative #

6 Introduction Interstate Highway 27/US Highway 87 (hereafter, IH 27) is a divided freeway that has its southern endpoint in Lubbock, Texas, and its northern endpoint in Amarillo, Texas. The city of Plainview is situated approximately 40 miles north of Lubbock; IH 27 runs through a heavily commercial section on the western side of the city. Within the city limits, US Highway 70 (US 70,) known locally as Olton Road, intersects IH 27 in a diamond interchange with two-way frontage roads in each quadrant. Figure 1 below illustrates the site layout of the area near the intersection. 6

7 Figure 1: Site Overview The northwest quadrant is particularly developed for commercial properties. Several restaurants and small shops are situated on the west frontage road, and a large retail shopping establishment is located about 600 feet west of the freeway. The primary entrances to all of these facilities are in the form of driveways along the IH 27 west frontage road. As a result, there is considerable traffic demand on this segment of frontage road. Owing to the fact that the commercial destinations on the west frontage road are all accessible from origin nodes on all four sides of the interchange, the existing two-lane, two-way frontage road on the northwest quadrant is 7

8 over capacity and experiences severe delays and queue lengths at peak periods. With the congestion, the intersection has experienced increased crash incidence and severity. Additionally, the other approaches to the intersection have suffered reduced levels of service due to the high demand on the southbound movement on the west side of the interchange. The existing traffic signal timing creates a condition where the southbound movement on the west side of the interchange and the westbound movement on the east side compete for green time. Thus, any improvement to one comes at the detriment to the other. Project Objectives The Texas Department of Transportation (TXDOT) has expressed interest in designing solutions to the problem. It has proposed four alternatives to be considered as solutions. The goal of the project described in this report was to analyze each design alternative from a traffic engineering perspective and evaluate the relative merits of each. From this analysis, a recommendation was formulated as to the most appropriate countermeasures for congestion mitigation along the IH 27 frontage roads. The four alternatives that were evaluated were progressively more costly to implement, but yielded increasing benefits with respect to signal capacity. They are described below: 1. No changes to pavement or markings signal timing changes only. The existing pavement marking configuration would remain as is, with one 20 feet wide lane for all southbound movements and one 12 feet wide lane for all northbound traffic on the west frontage road, with an 8 feet paved shoulder on the east side of the frontage road. There would be no disruption to normal traffic flow as a result of this modification. See Figure 2 below. 8

9 Figure 2: Existing Layout 2. No changes to pavement; restriping the northwestern quadrant from the existing configuration described above to add an additional lane for southbound traffic. The new outside lane would be 11 feet wide and would serve through and right turn traffic while the inside lane would be 10 feet wide and would serve left turn traffic. The existing northbound lane would be narrowed from 12 feet to 11 feet. Disruption to normal traffic would be light; the only traffic control measures required would be during the time the pavement marking removal and replacement occurred. Two variant designs were investigated the first variant did not provide a protected left turn movement for southbound traffic on the west frontage road, while the second variant did provide a protected turn phase. See Figure 3 below. 9

10 Figure 3: Design Alternatives #2-1 and # Widening the existing pavement from 40 feet to 46 feet, then modifying the pavement marking to allow three 11 feet wide lanes for southbound traffic (one each for right turn, through, and left turn, with the possibility to leave the through lane as a left turn/through option lane.) Northbound traffic would have one 11 feet wide lane and the shoulder would be narrowed to 2 feet. This alternative would require the relocation of the existing traffic signal pole for northbound traffic on the west side of the interchange, plus the demolition and construction of curb and gutter. Disruption to normal traffic would be light to moderate as this design requires the installation of new pavement, the removal and installation of curb and gutter, pavement marking, new traffic signal poles, and possibly the installation of new conduit and ground boxes. Three variants were investigated; the first variant allowed only permissive left turns from only the inner lane of the 10

11 southbound approach on the west frontage road, while the second variant provided a protected left turn phase. The third variant included a through/left turn option lane as well as a left turn only lane. See Figures 4 and 5 below. Figure 4: Design Alternatives #3-1 and #3-2 (No Through/ Left Turn Option Lane) 11

12 Figure 5: Design Alternative #3-3 (Through/Left Turn Option Lane Allowed) 4. Redesign the interchange to one-way frontage road operation on all quadrants. This alternative requires the construction of new pavement to widen the northwest approach to 46 feet, plus the addition of free U-turn lanes on the north and south sides of the interchange. An adequate design would also require the relocation of several signal poles, ground boxes, conduit, curb and gutter, and pavement marking, and would likely require the design of a full PS&E package. Existing traffic in the area would be substantially disrupted due to construction. See Figure 6 below. 12

13 Figure 6: Design Alternative #4 Methodological Approach The data to be used in the analysis was provided by TxDOT and supplemented by data collected during site visits to the interchange. Turn bay lengths, lane widths, and clearance distances were established by field measurement. Video of existing traffic was recorded at three peak periods (AM, Noon, and PM peaks) and was used for calibration of the existing traffic simulation model. Several software packages were considered for use during this project, including VISSIM (PTV, 2006,) Synchro 7 (Trafficware, 2007,) PASSER III (TTI, 1998,) and CORSIM (FHWA, 2006). After evaluation, it was decided to utilize Synchro 7 to model the intersection and establish level of service and other operational characteristics for both the existing and proposed configurations. 13

14 The methodological process used to construct the model and simulation was performed in the following steps: 1. The first step was the creation of the existing model. The geometric information about the intersection was obtained from TxDOT plans and site visits, and supplemented by images obtained from Google Earth. 2. After the existing geometry was created for the roadway network near the intersection, traffic data was input to the model. Traffic data was provided by TxDOT. 3. Existing signal timing information was coded into the model. The interchange was modeled as a 4-phase diamond, modified to allow two-way frontage road traffic. Signal timing data was provided by TxDOT. 4. Calibration of the model to fit calculated delay and queue length results with observed conditions. This step was especially important, because the driveway density on the west side of the northwest quadrant is such that the simulation initially calculated delay values incorrectly. The problem was solved by summing the delays expected for each driveway and adding it to the calculated delay for the signalized intersection. 5. Modification of the existing conditions model to reflect the proposed design alternatives and evaluating each for network performance measures. 6. Evaluation of all alternatives and selection of the design with the highest cost-to-benefit ratio. Formulation of recommendation based on the minimum level of reconstruction effort required to achieve the desired level of service. 14

15 Summary of Research Results and Recommendations After calibration of the existing model to reflect field conditions, intersection performance benchmarks were established. The existing signal timing consists of fully actuated, uncoordinated operation. If all movements reach their maximum green times, the signal would make a complete service cycle every 156 seconds. This mode of operation is continuous throughout the day; there are no time of day timing changes currently in place. The existing intersection timing is summarized in Table 1 below. Table 1: Existing s Phase # Direction of E/W (east (east E/W WBLT (east side overlap with phase 3) EBLT (east side overlap with phase 1) Table 2: Existing Levels of Service West Side Time of EBL EBT EBR WBL WBT WBR NBLTR SBTL SBR AM E E C A A A C E A Noon E E B A A E E F C PM F E B A A F E F C Table 3: Existing Levels of Service East Side Time of EBL EBT EBR WBL WBT WBR NBLTR SBTLR AM A A A E E B D C Noon A B A E E B E C PM A A A F E B F E As shown in these three tables, the most critical movements at the intersection are the southbound left and through movements on the west side (which share a single lane) and the northbound movement 15

16 on the east side, where left and right turn traffic shares a single lane with through traffic. Additionally, the eastbound movement on the west side and the westbound movement on the east side experience levels of service in the E/F range throughout the day. Alternative #1 The intent of this project was to determine to what extent the level of service could be improved by a series of increasingly complex modifications. The first alternative, timing changes with no pavement or marking changes, yielded significant improvements in capacity. The proposed changes, and the expected levels of service which result, are shown in Tables 4-6 below. Table 4: Alternative #1 Proposed s Phase # Direction of AM Peak Noon Peak PM Peak E/W (east (east E/W WBLT (east side overlap with phase 3) EBLT (east side overlap with phase 1) Table 5: Alternative #1 Levels of Service West Side Time of EBL EBT EBR WBL WBT WBR NBLTR SBTL SBR AM D D B A A A B C A Noon D E B A A B C F A PM D D B A A B C F A 16

17 Table 6: Alternative #1 Levels of Service East Side Time of EBL EBT EBR WBL WBT WBR NBLTR SBTLR AM A A A D D B C C Noon A A A D E A D C PM A A A D E B E C As shown in Table 4-6, the split times for most phases have been reduced. The cycle length for the signal would be 110 seconds if all phases were to extend to their maximum allowable green times. This proves effective because of a situation which arises as a result of origin/destination pairings near the intersection. The southbound movement on the west side is actually striped as a single lane. However, the lane is 20 feet wide and its effective configuration is that of a left/straight option and a right turn only lane. Drivers note that the pavement is wide enough for them to use the extra space for a right turn only lane, and so they proceed to bypass the through/left queue whenever possible to make the right turn. Observation in the field indicates that there is approximately 100 feet of right turn bay length available for this maneuver; driveways nearby inhibit the ability of drivers to utilize all available pavement width. Therefore, it may be concluded that the southbound lane configuration is equivalent to one left/straight/right option lane and a right turn only lane with 100 feet of storage. A similar situation arises on the east side of the intersection with westbound traffic. There is a heavy movement of westbound right turns onto the west frontage road for drivers who wish to visit the commercial establishments in the northwest quadrant of the intersection. Therefore, the northernmost westbound lane experiences much heavier traffic than the other through lanes. Although there are three lanes available for westbound through movements, the northernmost lane carries a disproportionate amount of this traffic because drivers know that they must be in that lane if they wish to easily make a right turn onto the west frontage road on the west side of the intersection. The queue from this single lane extends to a location several hundred feet from the intersection and prevents westbound traffic from 17

18 accessing the other through lanes. Therefore, this approach may be considered as having storage limitations as well. Since these movements experience storage failures, it is reasonable to expect that a shorter cycle length would improve delay and level of service values. With a shorter cycle, queues have a shorter time to build between each green cycle and therefore can empty more times per hour than with a longer cycle. As a result, the queue failures become less important to the overall performance of the intersection. Tables 7 and 8 below summarize the improvements to delay that are expected as a result of implementing Alternative #1, timing changes only. Table 7: Alternative #1 Delay Values vs. Existing Delay Values (West Side) Time of Delay AM EBL EBT EBR WBL WBT WBR NBLTR SBTL SBR Existing Proposed Change Change % -34% -34% -23% 100% 0% -43% -48% -18% -21% Noon EBL EBT EBR WBL WBT WBR NBLTR SBTL SBR Existing Proposed Change Change % -22% -13% 0% 100% 100% -37% -67% -53% -59% PM EBL EBT EBR WBL WBT WBR NBLTR SBTL SBR Existing Proposed Change Change % -13% -23% -7% 50% 100% -24% -61% -45% -54% 18

19 Table 8: Alternative #1 Delay Values vs. Existing Delay Values (East Side) Time of Delay Values AM EBL EBT EBR WBL WBT WBR NBLTR SBLTR Existing Proposed Change Change % 0% 0% 0% -33% -32% -24% -28% -30% Noon EBL EBT EBR WBL WBT WBR NBLTR SBTL Existing Proposed Change Change % 0% -88% 0% -29% -15% 0% -32% -43% PM EBL EBT EBR WBL WBT WBR NBLTR SBTL Existing Proposed Change Change % 0% -67% 0% -38% 3% 0% -31% -33% Alternative #2 Alternative #2 involves the striping of a right-turn only lane for the southbound approach on the west frontage road. There are two options available for this design alternative: Alternative #2-1 involves the conversion of the existing left/through/right lane into a left turn only lane and striping an extra lane to be used for through and right turn traffic. Signal timing will be optimized for the intersection, but no phasing changes will be installed. Alternative #2-2 involves the conversion of the existing left/through/right lane into a left turn only lane and striping an extra lane to be used for through and right turn traffic. Signal timing will be optimized and a protected left-turn phase will be installed for southbound traffic on the west frontage road. During the protected turn phase, southbound through and left turn traffic will move simultaneously. 19

20 Table 9 below shows the proposed split times for each alternative design. Tables 10 and 11 illustrate the expected levels of service for design alternative #2-1. Tables 12 and 13 show delay improvements over the existing condition with the implementation of design alternative #2-1. Table 9: Alternative #2-1 Proposed s Phase # Direction of AM Peak Noon Peak PM Peak E/W (east (east E/W WBLT (east side overlap with phase 3) EBLT (east side overlap with phase 1) Table 10: Alternative #2-1 Levels of Service West Side Time of EBL EBT EBR WBL WBT WBR NBLTR SBTL SBR AM D D B A A A B C B Noon D E B A A D C F B PM E D B A A F C F C Table 11: Alternative #2-1 Levels of Service East Side Time of EBL EBT EBR WBL WBT WBR NBLTR SBTLR AM A A A D D B C C Noon A A A D D A D B PM A A A D D A E D 20

21 Table 12: Alternative #2-1 Delay Values Vs. Existing Delay Values (West Side) Time of Delay AM EBL EBT EBR WBL WBT WBR NBLTR SBTL SBR Existing Proposed Change Change % -34% -35% -27% 0% 0% -43% -42% -18% 7% Noon EBL EBT EBR WBL WBT WBR NBLTR SBTL SBR Existing Proposed Change Change % -22% -14% 0% 0% 0% -37% -67% -39% -29% PM EBL EBT EBR WBL WBT WBR NBLTR SBTL SBR Existing Proposed Change Change % -21% -27% -7% 50% 100% -23% -57% -40% -43% 21

22 Table 13: Alternative #2-1 Delay Values Vs. Existing Delay Values (East Side) Time of Delay Values AM EBL EBT EBR WBL WBT WBR NBLTR SBLTR Existing Proposed Change Change % 0% 0% 0% -33% -32% -24% -33% -36% Noon EBL EBT EBR WBL WBT WBR NBLTR SBTL Existing Proposed Change Change % 100% -88% 0% -33% -29% -10% -34% -43% PM EBL EBT EBR WBL WBT WBR NBLTR SBTL Existing Proposed Change Change % 100% -67% 0% -40% -29% -10% -33% -33% When compared to the results that are achieved under Alternative #1, the improvements expected from Alternative #2-1 are at best marginal, and in some cases less desirable. An example of this is the southbound right turn movement the improvement in the expected delay value is 10% - 20% less than under Alternative #1. Alternative #2-2 involves the installation of a right/through option lane and conversion of the existing southbound lane into a left turn only lane. Additionally, the intersection timing will be modified to allow a protected southbound left turn on the west frontage road approach. The proposed split times, levels of service, and expected improvements in delay over the existing condition are shown in tables below. 22

23 Table 14: Alternative #2-2 Proposed s Phase # Direction of AM Peak Noon Peak PM Peak E/W (east (east E/W WBLT (east side overlap with phase 3) EBLT (east side overlap with phase 1) SBLT Table 15: Alternative #2-2 Levels of Service West Side Time of EBL EBT EBR WBL WBT WBR NBLTR SBL SBTR AM E E B A A A C D B Noon E F B A A E C F C PM F E B A A F C F C Table 16: Alternative #2-2 Levels of Service East Side Time of EBL EBT EBR WBL WBT WBR NBLTR SBTLR AM A A A D E B C C Noon A A A D F B D B PM A A A E F B E D 23

24 Time of Table 17: Alternative #2-2 Delay Values Vs. Existing Delay Values (West Side) Delay AM EBL EBT EBR WBL WBT WBR NBLTR SBL SBTR* Existing N/A Proposed Change N/A Change % -21% -23% -14% 500% 500% -14% -15% -34% N/A Noon EBL EBT EBR WBL WBT WBR NBLTR SBL SBTR* Existing N/A Proposed Change N/A Change % -3% 38% 15% 400% 400% 13% -55% -77% N/A PM EBL EBT EBR WBL WBT WBR NBLTR SBL SBTR* Existing N/A Proposed Change N/A Change % 16% 3% 7% 300% 500% -6% -45% -80% N/A *Since this configuration limits right turns on red, it is not possible to directly compare the existing delay for right turn and through traffic to the delay for this proposed design alternative. 24

25 Table 18: Alternative #2-2 Delay Values Vs. Existing Delay Values (East Side) Time of Delay Values AM EBL EBT EBR WBL WBT WBR NBLTR SBLTR Existing Proposed Change Change % 0% 0% 0% -22% -22% -12% -31% -33% Noon EBL EBT EBR WBL WBT WBR NBLTR SBTL Existing Proposed Change Change % -50% -69% 0% -10% 53% 20% 100% 10% PM EBL EBT EBR WBL WBT WBR NBLTR SBTL Existing Proposed Change Change % 0% -50% 0% -20% 95% 20% 77% -5% Comparing the values in Tables 17 and 18 to the values in Tables 7 and 8 illustrate that adding a left turn only lane does not provide a great deal of additional capacity to the intersection. Even providing a protected left turn movement does not provide a significant amount of additional capacity. The extra southbound left turn capacity on the west side of the intersection that the protected movement provides is counteracted by the reduction in capacity for the northbound movement. Therefore, it is not recommended to install the improvements associated with this alternative. Alternative #3 Alternative #3 involves the installation of new pavement and the addition of two additional lanes for southbound traffic on the west frontage road. This alternative would provide one right turn only lane, one through lane, and one left turn only lane instead of the existing configuration of one lane for all traffic. Lane widths would be narrowed for the northbound and southbound approaches. This alternative would 25

26 also require the relocation of curb and gutter and traffic signal poles. There are three options available with this design alternative: Alternative #3-1 involves the conversion of the existing left/through/right lane into a left turn only lane, a through only lane, and a right turn only lane. Signal timing will be optimized for the intersection, but no phasing changes will be installed. Alternative #3-2 involves the installation of a right turn only lane, through only lane, and a left turn only lane as discussed above. Additionally, the signal timing and phasing will be modified to allow a protected left turn movement for southbound left turn traffic. Alternative #3-3 is the same as alternative #3-1 but with the through lane also allowing a left turn option. This may require adjustment of pavement marking at the intersection. The option lane s presence would necessitate the installation of split phasing in the event that a protected left turn phase were desired; for this reason, Alternative #3-3 examines permissive turns only and disregards the protected option as not viable. Table 19 below shows the proposed split times for each alternative design. Tables 20 and 21 illustrate the expected levels of service for design alternative #3-1. Tables 22 and 23 show delay improvements over the existing condition with the implementation of design alternative #

27 Table 19: Alternative #3-1 Proposed s Phase # Direction of AM Peak Noon Peak PM Peak E/W (east (east E/W WBLT (east side overlap with phase 3) EBLT (east side overlap with phase 1) Table 20: Alternative #3-1 Levels of Service West Side Time of EBL EBT EBR WBL WBT WBR NBLTR SBL SBT SBR AM D D B A A A B C C A Noon D E B A A D C F C A PM E D B A A F C F C A 27

28 Table 21: Alternative #3-1 Levels of Service East Side Time of EBL EBT EBR WBL WBT WBR NBLTR SBTLR AM A A A D D B C C Noon A A A D D A D B PM A A A D D A E D Time of Table 22: Alternative #3-1 Delay Values Vs. Existing Delay Values (West Side) Delay AM EBL EBT EBR WBL WBT WBR NBLTR SBL SBT SBR Existing Proposed Change Change % -34% -35% -23% 0% 0% -43% -42% -20% -42% -36% Noon EBL EBT EBR WBL WBT WBR NBLTR SBL SBT SBR Existing Proposed Change Change % -31% -11% 0% 0% 100% -37% -67% -53% -71% -74% PM EBL EBT EBR WBL WBT WBR NBLTR SBL SBT SBR Existing Proposed Change Change % -13% -23% -7% 50% 100% -25% -59% -57% -75% -80% 28

29 Table 23: Alternative #3-1 Delay Values Vs. Existing Delay Values (East Side) Time of Delay Values AM EBL EBT EBR WBL WBT WBR NBLTR SBLTR Existing Proposed Change Change % 0% 0% 0% -33% -32% -24% -33% -36% Noon EBL EBT EBR WBL WBT WBR NBLTR SBTL Existing Proposed Change Change % 100% -88% 0% -47% -29% -10% -34% -43% PM EBL EBT EBR WBL WBT WBR NBLTR SBTL Existing Proposed Change Change % 100% -67% 0% -40% -29% -10% -33% -33% As shown in Tables 22 and 23, Alternative #3-1 provides a much improved level of service for southbound traffic on the west frontage road. Delays in the noon and PM peaks show significant reduction, especially for the right turn and through movements. Since through and right turn traffic have their own lanes and no longer share delay times with the other movements, they experience much less delay. Alternative #3-2 provides the same lane configuration as alternative #3-1 but also provides a protected left turn movement in addition to the permissive movement. Table 24 shows the proposed split times for the intersection phases under alternative #3-2. Tables show the expected levels of service and delay times that will result from implementation of alternative #

30 Table 24: Alternative #3-2 Proposed s Phase # Direction of AM Peak Noon Peak PM Peak E/W (east (east E/W WBLT (east side overlap with phase 3) EBLT (east side overlap with phase 1) SBLT Table 25: Alternative #3-2 Levels of Service West Side Time of EBL EBT EBR WBL WBT WBR NBLTR SBL SBT SBR AM E E B A A A C D C A Noon D F B A A D C F C A PM F E B A A F C F C A Table 26: Alternative #3-2 Levels of Service East Side Time of EBL EBT EBR WBL WBT WBR NBLTR SBTLR AM A A A D E B C C Noon A A A D F B D B PM A A A E F B E D 30

31 Table 27: Alternative #3-2 Delay Values Vs. Existing Delay Values (West Side) Time of Delay AM EBL EBT EBR WBL WBT WBR NBLTR SBL SBT SBR Existing Proposed Change Change % -18% -19% -14% 500% 500% -43% -21% -38% -28% -29% Noon EBL EBT EBR WBL WBT WBR NBLTR SBL SBT SBR Existing Proposed Change Change % -8% 38% 15% 400% 400% -86% -55% -79% -77% -89% PM EBL EBT EBR WBL WBT WBR NBLTR SBL SBT SBR Existing Proposed Change Change % 16% 3% 7% 300% 500% -6% -45% -78% -75% -89% 31

32 Table 28: Alternative #3-2 Delay Values Vs. Existing Delay Values (East Side) Time of Delay Values AM EBL EBT EBR WBL WBT WBR NBLTR SBLTR Existing Proposed Change Change % 0% 0% 0% -19% -18% -12% 6% 0% Noon EBL EBT EBR WBL WBT WBR NBLTR SBTL Existing Proposed Change Change % -50% -69% 0% -10% 51% 20% -2% -24% PM EBL EBT EBR WBL WBT WBR NBLTR SBTL Existing Proposed Change Change % 0% -50% 0% -20% 95% 20% 77% -5% Tables 27 and 28 show that the addition of a protected left turn phase for southbound traffic on the west frontage road provides a marginal improvement in delay for all southbound movements, but significantly increases the delay experienced by the opposing northbound movement. Virtually all other movements on both sides of the intersection remain unchanged. Alternative #3-3 is the same scenario as alternative #3-1 except that the middle (through) lane for southbound traffic on the west frontage road is configured as a through/left turn option lane. All left turns operate permissively. Table 29 below shows the proposed split times for all phases. 32

33 Table 29: Alternative #3-3 Proposed s Phase # Direction of AM Peak Noon Peak PM Peak E/W (east (east E/W WBLT (east side overlap with phase 3) EBLT (east side overlap with phase 1) Table 30: Alternative #3-3 Levels of Service West Side Time of EBL EBT EBR WBL WBT WBR NBLTR SBL SBT SBR AM D D B A A A B C C A Noon D E B A A D C D D A PM E D B A A F C D D A Table 31: Alternative #3-3 Levels of Service East Side Time of EBL EBT EBR WBL WBT WBR NBLTR SBTLR AM A A A D D B C C Noon A A A D D A D B PM A A A D D A E D Table 32: Alternative #3-3 Delay Values Vs. Existing Delay Values (West Side) 33

34 Time of Delay AM EBL EBT EBR WBL WBT WBR NBLTR SBL SBT SBR Existing Proposed Change Change % -34% -34% -23% 0% 0% -43% -42% -24% -24% -29% Noon EBL EBT EBR WBL WBT WBR NBLTR SBL SBT SBR Existing Proposed Change Change % -27% -13% 0% 0% 100% -37% -66% -71% -70% -86% PM EBL EBT EBR WBL WBT WBR NBLTR SBL SBT SBR Existing Proposed Change Change % -13% -23% -7% 50% 100% -25% -59% -61% -70% -89% Table 33: Alternative #3-3 Delay Values Vs. Existing Delay Values (East Side) Time of Delay Values AM EBL EBT EBR WBL WBT WBR NBLTR SBLTR Existing Proposed Change Change % 0% 0% 0% -33% -32% -24% -33% -36% Noon EBL EBT EBR WBL WBT WBR NBLTR SBTL Existing Proposed Change Change % 50% -94% 0% -47% -29% -10% -34% -43% PM EBL EBT EBR WBL WBT WBR NBLTR SBTL Existing Proposed Change Change % 100% -83% 0% -40% -29% -10% -33% -33% 34

35 Compared to alternative #3-1, the improvement in delay for southbound traffic on the west frontage road is slight. As expected, the through movement suffers a slight degradation of capacity due to the effect of left turning traffic out of the through lane. However, this alternative is expected to cost more than alternative #3-1 due to the extra costs of installing new pavement markings for a dual left turn lane. More importantly, it will reduce the overall safety of the intersection by allowing permissive turns from two lanes. Experience has shown that drivers do not correctly anticipate the extra time required to make the left turn out of the outer lane, and this leads to additional right-angle collisions with northbound through vehicles. The marginal improvement in level of service is deemed insufficient to justify recommending this alternative over #

36 Alternative #4 Alternative #4 is the most far-reaching of the proposed design alternatives. This option would involve the complete redesign of the intersection, both from a signal timing and geometric perspective. The existing two-way frontage roads would be reconstructed as one-way frontage roads. Dedicated U- turn lanes would be installed for the northbound and southbound approaches. This redesign would necessitate several geometric changes, including the restriping of all approaches, relocation of curb and gutter and signal poles, and new signage. It would also represent a completely different interchange configuration which the traveling public would have to become accustomed to. Design and construction costs would be substantial, as would disruption to traffic flow during construction. The proposed configuration was modeled in Synchro. The proposed split times and levels of service are shown in Tables 34-36, and the expected delay values are shown in Tables 37 and 38. Table 34: Alternative #4 Proposed s Phase # Direction of AM Peak Noon Peak PM Peak E/W (east NB (east E/W SB WBLT NB (east side overlap with phase 3) EBLT (east SB side overlap with phase 1)

37 Table 35: Alternative #4 Levels of Service West Side Time of EBT EBR WBL WBT SBL SBTR AM D B A A C C Noon D A A A D C PM D A A A D C Table 36: Alternative #4 Levels of Service West Side Time of EBL EBT WBT WBR NBL NBTR AM A A D B C B Noon A A D C C C PM A A D F C C Table 37: Alternative #4 Delay Values Vs. Existing Delay Values (West Side) Time of Delay AM EBT EBR WBL WBT SBL* SBTR* Existing Proposed Change Change % -41% -55% 300% 0% -68% -72% Noon EBT EBR WBL WBT SBL* SBTR* Existing Proposed Change Change % -38% -23% 0% -50% -83% -83% PM EBT EBR WBL WBT SBL* SBTR* Existing Proposed Change Change % -37% -29% 33% -67% -82% -82% * Since the lane configurations have changed, direct comparison of delay times between existing and new configurations is not possible. Delays shown for existing southbound movements are for the single existing lane. 37

38 Table 38: Alternative #4 Delay Values Vs. Existing Delay Values (East Side) Time of Delay AM EBL EBT WBT WBR NBL* NBTR* Existing Proposed Change Change % 100% 100% -43% -6% -31% -72% Noon EBL EBT WBT WBR NBL* NBTR* Existing Proposed Change Change % 300% 200% -46% 240% -43% -63% PM EBL EBT WBT WBR NBL* NBTR* Existing Proposed Change Change % 100% -83% -52% 760% -60% -61% * Since the lane configurations have changed, direct comparison of delay times between existing and new configurations is not possible. Delays shown for existing northbound movements are for the single existing lane. Significant improvements are expected for the frontage road traffic as a result of implementing Alternative #4. Since westbound right turns are no longer allowed onto the west frontage road, the redistribution of the volume which currently make use of this movement will negatively impact the traffic network in other areas. Overall, this is the best option from a traffic operations standpoint, but it comes at a much higher monetary and time cost than the other alternatives. Summary and Recommendation Each alternative presented in this report has benefits and costs. From a simple capacity perspective, conversion of the interchange into a traditional diamond with one-way frontage roads on all four quadrants offers the highest capacity. This improvement in capacity will result in a cost that is orders of magnitude higher than the implementation of any of the less robust design alternatives. 38

39 It is clear from the analysis described above that the intersection will experience an improvement in both capacity and safety with the implementation of any of these design alternatives. However, one plan of action presents itself as an ideal path from immediate improvement of the intersection s capacity to ultimate build-out. The following actions are recommended to TXDOT as a long-range plan for improvement of the intersection of IH 27 and US Hwy 70 in Plainview, Texas: Deploy the signal timing changes associated with Alternative #1 immediately. These changes are straightforward and simple to implement, and will improve intersection capacity immediately as shown in Tables 7 and 8. Design signal, pavement marking, and signage plans to implement Alternative #3-1 (widening of pavement, installation of additional lanes for southbound traffic on the west frontage road, some relocation of signal equipment.) Ensure that to whatever extent possible, the design accounts for a future build-out of the intersection to a standard diamond interchange with one-way frontage roads. Construction and installation of Alternative #3-1 should commence as soon as is practical. Update the long-range plan for this area to include conversion of the frontage roads from twoway to one-way. When funds are made available, implement Alternative #4 (conversion of all frontage roads to one-way traffic, installation of U-turn lanes for northbound and southbound traffic, and complete signal redesign.) This path of action has the benefits of being scalable to the Department s funding restraints while at the same time providing a plan for improvement in the short, medium, and long terms. 39