Transportation Knowledge

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1 FE REVIEW COURSE SPRING 2017 Transportation Engineering 4/26/2017 Transportation Knowledge 8-12 problems Traffic safety Traffic capacity Traffic flow theory Traffic control devices Transportation planning Pavement system design Geometric design of streets and highways Geometric design of intersections 2 1

2 Traffic Safety Crash rates for intersections are normally expressed in terms of crashes per million entering vehicles (MEV) RMEV= RMEV = crash rate per million entering vehicles A = number of crashes, total or by type occurring in a single year at the location V = ADT*365 ADT = average daily traffic (ADT) volumes entering the intersection) 3 Traffic Safety An intersection has a total entering traffic volume of 42,000 vehicles per day. During the past 3 years, there has been a total of 35 reported intersection-related crashes. What is the Crash rate for this intersection? RMEV= V=ADT*

3 Traffic Safety Crash rates for roadway segments are normally expressed in terms crashes per 100 million vehicle-miles (100 MVM). RMVM= RMVM = crash rate per hundred million vehicle miles A = number of crashes, total or by type at the study location, during a given period VMT = vehicle miles of travel during the given period; ADT*(number of days in a study period)*(length of road) ADT = average daily traffic on the roadway segment 5 Traffic Safety A five-mile long section of two-lane road has an ADT of 8,000. There have been six crashes on this section of road during the past two years. What is the crash rate? RMVM= VMT=ADT*(number of days in a study period)*(length of road) 6 3

4 Traffic Capacity Highway Capacity Manual Capacity analysis is the study of various types of highway facilities and their ability to carry traffic. Level-of-service (LOS) is a letter designation that describes a range of operating conditions on a particular type of facility. 7 Traffic Capacity 4 Steps to determine LOS Step 1 Compute Free Flow Speed (FFS) Step 2 Compute Flow Rate Step 3 Determine Density Step 4 - Determine LOS 8 4

5 Traffic Capacity 4 Steps to determine LOS Step 1 Compute Free Flow Speed (FFS) FFS = 75.4 F LW F LC 3.22TRD 0.84 FFS = Free flow speed of a basic freeway segment (mi/h) F LW = adjustment for lane width (mi/h) F LC = adjustment for right-side lateral clearance (mi/h) TRD = total ramp density (ramps/mi) 9 Traffic Capacity A 6-lane (3 lanes in each direction) freeway passes through level terrain in an urban area. The freeway is constructed with 11 ft lanes and concrete barriers 3 ft from the outer pavement edges of both outer lanes. The one-direction peak hourly volume during the weekday commute is 2200 vph. Traffic includes 4% buses, 6% trucks, and 2% recreational vehicles (RVs). There is one ramp per mile on average. The peak hour factor is The posted speed limit is 55 mph. Commuter traffic, F p = 1.0. What is the free flow speed? FFS = 75.4 F LW F LC 3.22TRD

6 Traffic Capacity 4 Steps to determine LOS Step 1 Compute Free Flow Speed (FFS) Step 2 Compute Flow Rate V P =demand flow rate under equivalent base conditions (pc/h/ln) V=demand volume under prevailing conditions (veh/h) PHF=Peak-hour factor N=number of lanes in analysis direction F HV = V p = F HV =adjustment factor for presence of heavy vehicles in traffic stream F P =adjustment factor for unfamiliar driver populations F HV =heavy-vehicle adjustment factor P T =proportion of trucks and buses in traffic stream P R =proportion of RVs in traffic stream E T =passenger-car equivalent (PCE) of one truck or bus in traffic stream E R =PCE of one RV in traffic stream 11 Traffic Capacity A 6-lane (3 lanes in each direction) freeway passes through level terrain in an urban area. The freeway is constructed with 11 ft lanes and concrete barriers 3 ft from the outer pavement edges of both outer lanes. The one-direction peak hourly volume during the weekday commute is 2200 vph. Traffic includes 4% buses, 6% trucks, and 2% recreational vehicles (RVs). There is one ramp per mile on average. The peak hour factor is The posted speed limit is 55 mph. Commuter traffic, F p = 1.0. What is the passenger car equivalent flow rate per lane? V p = F HV = 12 6

7 Traffic Capacity 4 Steps to determine LOS Step 1 Compute Free Flow Speed (FFS) Step 2 Compute Flow Rate Step 3 Determine Density D = D = density (pc/mi/ln) V p = demand flow rate (pc/h/ln) S = mean speed of traffic stream under base conditions (mi/h) 13 Traffic Capacity A 6-lane (3 lanes in each direction) freeway passes through level terrain in an urban area. The freeway is constructed with 11 ft lanes and concrete barriers 3 ft from the outer pavement edges of both outer lanes. The one-direction peak hourly volume during the weekday commute is 2200 vph. Traffic includes 4% buses, 6% trucks, and 2% recreational vehicles (RVs). There is one ramp per mile on average. The peak hour factor is The posted speed limit is 55 mph. Commuter traffic, F p = 1.0. What is the Density? D = 14 7

8 Traffic Capacity 4 Steps to determine LOS Step 1 Compute Free Flow Speed (FFS) Step 2 Compute Flow Rate Step 3 Determine Density Step 4 - Determine LOS LOS Density (pc/mi/ln) A 11 B >11 18 C >18 26 D >26 35 E >35 45 F >45 15 Traffic Capacity A 6-lane (3 lanes in each direction) freeway passes through level terrain in an urban area. The freeway is constructed with 11 ft lanes and concrete barriers 3 ft from the outer pavement edges of both outer lanes. The one-direction peak hourly volume during the weekday commute is 2200 vph. Traffic includes 4% buses, 6% trucks, and 2% recreational vehicles (RVs). There is one ramp per mile on average. The peak hour factor is The posted speed limit is 55 mph. Commuter traffic, F p = 1.0. LOS Density (pc/mi/ln) What is the weekday peak-hour level of service? A 11 B >11 18 C >18 26 D >26 35 E >35 45 F >

9 Traffic Flow Theory Greenshields Model D=density (veh/mi) S= speed(mi/hr) V=flow (veh/hr) V m =maximum flow D o =optimum density (critical density) D j =jam density S o =optimum speed S f =theoretical speed (free flow speed) 17 Traffic Flow Theory Which of the following is NOT true under Jam Density conditions? A. Density is maximum B. Density is zero C. Flow is zero D. Speed is zero 18 9

10 Traffic Flow Theory What are the characteristics of unstable flow? A. Flow increases, speed decreases B. Flow decreases, speed increases C. Flow Decreases, speed decreases D. Flow increases, speed increases 19 Traffic Control Devices Yellow Change Interval calculates the time required for a driver to make a decision to come to a safe stop. 3-6 seconds y=. y= length of yellow interval to nearest 0.1 sec (sec) t= driver reaction time (sec) V= vehicle approach speed (fps) a= deceleration rate (ft/sec 2 ) G= percent grade divided by

11 Traffic Control Devices Red Clearance Interval Allows additional time for motorist already in the intersection to clear the intersection on the red indication before a conflicting traffic movement is released 0.5 to 3.0 seconds r= r= length of red clearance interval to nearest 0.1 sec (sec) W = Width of intersection, curb-to-curb (ft) l= length of vehicle (ft) v= vehicle approach speed (fps) 21 Traffic Control Devices A signalized intersection has three legs, one WB, EB, and NB, the grade is 5% up hill on the steepest approach, speed limit is 40 mph, the intersection is 110 feet wide, deceleration rate of 11.2 ft/sec, and driver reaction time is 1 second and the design vehicle is 40 feet. Determine the yellow change interval? Determine the red clearance interval? y= r=

12 Transportation Planning (Travel Demand Forecasting) Attempts to quantify the amount of travel on a transportation system Involves dividing urban areas into a series of zones Is created by the physical separation of urban activities The supply of transportation is represented by the service characteristics of highway and transit networks. Four basic phases of travel-demand forecasting process: Trip generation forecasts the number trips that will be made Trip distribution determines where the trips will go Mode Choice predicts how the trips will be divided among the variable modes of travel Trip assignment (highway and transit) predicts the routes that the trips will take, resulting in traffic forecasts for the highway system and ridership forecasts for the transit system 23 Transportation Planning (Travel Demand Forecasting) A study determined that trips generated from a residential neighborhood is directly related to number of persons and number of autos per household. After conducting studies at different residential neighborhoods, the following relationship is established: Number of trips generated per household per day = P+2.1A Where: P=number of persons per household A=number of autos per household If a residential neighborhood contains 500 households with an average of 4.5 persons and 2.5 autos per household, how many trips this neighborhood is expected to generate per day? 24 12

13 Pavement System Design Pavement Design relies on the Structural Number (SN) from the AASHTO Guide for Design of Pavement Structures. Structural Number (SN) Represents the overall structural requirement needed to sustain traffic loads and is dependent on existing soil support, traffic loads, pavement serviceability, and environmental conditions. SN = a 1 D 1 +a 2 D 2 + +a n D n SN = Structural Number for the pavement a i =layer coefficient D i =thickness of layer (inches) 25 Pavement System Design Determine the thickness of flexible pavement layer 2 give the following: FACTS: Total Structural Number required=7.0 Total number of layers=2 Layer 1 consists of asphalt concrete with a strength coefficient of 0.46 Layer 1 thickness=6 inches Layer 2 consists of granular base with a strength coefficient of 0.15 SN = a 1 D 1 +a 2 D 2 + +a n D n 26 13

14 Geometric Design Topics Overview Horizontal Curves Spiral Curves Sight Distance Superelevation and Side Friction Factor Vertical Curves 27 Horizontal Curves Horizontal circular curve is a circular arc between two straight lines known as tangents P

15 Horizontal Curves Example (1) 29 Horizontal Curves Example (2) 30 15

16 Horizontal Curves Example (3) 31 Horizontal Curves Example (4) 32 16

17 Horizontal Curves Example (5) 33 Spiral Curves P

18 Spiral Curves Example 35 Superelevation and Side Friction Fractor P

19 Superelevation and Side Friction Factor Example 37 Vertical Curves P

20 Vertical Curves Example (1) 39 Vertical Curves Example (2) 40 20

21 Vertical Curves Example (3) 41 Sight Distance P

22 Straight-Ahead Stopping Sight Distance Example 43 Crest Vertical Curve Length Based on Stopping Sight Distance Example 44 22

23 Sag Vertical Curve Length Based on Stopping Sight Distance Example 45 THANK YOU 23