Development of Left-Turn Lane Warrants for Unsignalized Intersections (2013)

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81 CHAPTER 5 DELAY, CRASH, AND CONSTRUCTION COST STUDIES Left-turn lanes can provide benefits in safety as well as operations. Left-turn lanes can reduce the potential for collisions by providing safer left-turn operations. They can also reduce delay and improve left-turn capacity by removing stopped left-turn vehicles from the main travel lane. A benefit-cost approach to justify right-turn deceleration lanes was presented by Potts et al. (58). The benefits of the right-turn lane were determined for crash reduction (change in number of crashes) and delay reduction (improvements in arterial capacity from removing the slower- moving vehicles from the main traffic stream). The cost of the right-turn lane reflected construction costs. This chapter presents a similar approach to determine when a left-turn lane would be justified. The steps include:  Identify an economic analysis procedure,  Use simulation to determine delay savings from installing a left-turn lane and delay increase from a new development,  Calculate crash costs and crash reduction savings using safety performance functions and crash accident modification factors from the Highway Safety Manual (77), and  Determine construction cost. ECONOMIC ANALYSIS PROCEDURE Economic analysis can provide a useful method for combining traffic operations and safety benefits of left-turn lanes to identify situations in which left-turn lanes are and are not justified economically. The following equation shows how to calculate the benefit-cost ratio: ஻ ஼ ൌ ஽௘௟௔௬ ோ௘ௗ௨௖௧௜௢௡ାௌ௔௙௘௧௬ ூ௠௣௥௢௩௘௠௘௡௧௦ ܥ݋݊ݏݐݎݑܿݐ݅݋݊ ஼௢௦௧௦ (20) When the B/C ratio exceeds 1.0, a left-turn lane is considered economically justified because the benefits are greater than the costs. The following equations provide an overview of the components needed for the evaluation of left-turn lanes: ஻ ஼ ൌ ൣሼ஽ோሺ௏೅ೃ,௏ಽ೅,ு௥ሻൈ஽஼ሽା൛ۃேೞ೛೑൫஺஽்೘ೌೕ,஺஽்೘೔೙൯ሺଵି஺ெிಽ೅ሻۄൈ஺஼ൟ൧ൈ௎ௌ௉ௐிሺ௜,௡ሻ ஼஼ (21) ܷܹܵܲܨሺ݅, ݊ሻ ൌ ሺଵା௜ሻ೙ିଵ௜ሺଵା௜ሻ೙ (22)

82 Where: B/C = benefit-cost ratio; DR(VTR, VLT, Hr) = delay reduction (veh-hr/year) from left-turn lane installation as a function of VTR, VLT, Hr; VTR = major-road volume during the traffic period of interest (veh/hr); VLT = left-turn volume during the traffic period of interest (veh/hr); Hr = number of hours in a year for the traffic period of interest (hr); DC = user cost savings from delay reduction ($/veh-hr); Nspf(ADTmaj, ADTmin) = safety performance function to estimate the intersection-related predicted average crash frequency for base conditions; AMFLT = accident modification factor for installation of a left-turn lane; AC = user cost savings from crash reduction ($/crash); USPWF(i,n) = uniform series present worth factor as a function of i and n; I = minimum attractive rate of return expressed as a decimal (i.e., 0.04 for a 4 percent return); n = number of years; and CC = estimated construction cost for a left-turn lane ($). The B/C ratio is composed of two major components: • Benefit in crash reduction and • Benefit in reduction of travel time delays. Both of these terms are multiplied by the uniform series present worth factor to convert them from annual benefit amounts to the present value of a time series of annual benefits. DELAY Scenarios Computer simulation was used to evaluate the operational benefits of a left-turn lane on intersection delay at an unsignalized intersection. The purpose of the effort was to assess the delay savings from installing a left-turn lane. The key operational issue related to left-turn lanes at unsignalized intersections or driveways is the operational delay to traffic on the major street. If there is substantial delay to through traffic caused by queued left-turn vehicle(s), provision of a left-turn lane can reduce that delay. Two scenarios were explored: • Existing site and • New development. In the existing site scenario, the comparison identifies the benefits when the left turns at an existing driveway or intersection are provided a left-turn lane. The total average delay for when a left-turn lane is present is subtracted from the total average delay when a left-turn lane is not present. This difference represents the total average delay savings per vehicle at the intersection on the major roadway.

83 In the second scenario, the baseline condition is that no delay is present at the location because there is no left-turn demand. When a new development is proposed, the added delay to the system is determined from simulation. The total average delay for the without left-turn lane scenario represents the anticipated delay being added to the system when a new development creates left-turn demand. Simulation To conduct the operational analysis of left-turn lanes, a microsimulation model (VISSIM) was used to measure the impact of left-turn vehicles on intersection delay. The following variables were examined: • Presence of a left-turn lane (yes or no); • Number of through lanes on the major street (two or four); • Left-turn lane volume (20, 60, 100, or 140 veh/hr); • Through traffic volume: o Two lanes on the major road: 400, 600, or 800 veh/hr/approach or o Four lanes on the major road: 400, 800, or 800 veh/hr/lane; and • Traffic speed on the major road: 30, 40, or 50 mph. Assumptions included: • Arrival is random. • The standard deviation for speeds is 5 mph. • The critical gap for left-turning vehicles is 5 sec. • The default traffic composition is 98 percent automobiles and 2 percent trucks. • The unsignalized intersections and driveways considered have no traffic control requiring a stop or yield by vehicles on the major street. • The left-turn lane, when present, is long to avoid having queue spillbacks from the lane. A series of simulation modeling runs were conducted. To evaluate delay, each volume scenario was modeled without a left-turn lane and again with a left-turn lane. Ten runs were conducted per scenario. The system-wide measure of performance used was average delay per vehicle for the whole network, measured in seconds. To determine the benefit of adding a left-turn lane, the difference between the average total delays with and without a left-turn lane was calculated. This value represents the operational benefit of having a left-turn lane at an existing site. Figure 23 illustrates the delay reductions, while Figure 24 illustrates the added delay due to a new development. A review of the data revealed that delay: • Increases as the number of left-turn vehicles increases, • Increases as the volume on the major road increases, • Decreases or is relatively constant as the speed limit increases for two-lane highways, • Increases or is relatively constant as the speed limit increases for four-lane highways, and • Decreases or is relatively constant as the number of lanes increases (with the exception of a 600- or 800-veh/hr/ln approach volume, 140-veh/hr left-turning volume, and 50-mph speed limit).

84 Figure 23. Simulation-estimated delay reduction when adding a left-turn lane at an existing site. 0 1 2 3 4 5 0 50 100 150 D el ay R ed uc ti on ( se c/ ve h) Left-Turn Volume (veh/hr) 2 lanes, 400 veh/hr/approach 30 mph 40 mph 50 mph 0 2 4 6 8 10 12 14 16 18 20 0 50 100 150 D el ay R ed uc ti on ( se c/ ve h) Left-Turn Volume (veh/hr) 4 lanes, 400 veh/hr/ln 30 mph 40 mph 50 mph 0 1 2 3 4 5 0 50 100 150 D el ay R ed uc ti on ( se c/ ve h) Left-Turn Volume (veh/hr) 2 lanes, 600 veh/hr/approach 30 mph 40 mph 50 mph 0 2 4 6 8 10 12 14 16 18 20 0 50 100 150 D el ay R ed uc ti on ( se c/ ve h) Left-Turn Volume (veh/hr) 4 lanes, 600 veh/hr/ln 30 mph 40 mph 50 mph 0 1 2 3 4 5 0 50 100 150 D el ay R ed uc ti on ( se c/ ve h) Left-Turn Volume (veh/hr) 2 lanes, 800 veh/hr/approach 30 mph 40 mph 50 mph 0 2 4 6 8 10 12 14 16 18 20 0 50 100 150 D el ay R ed uc ti on ( se c/ ve h) Left-Turn Volume (veh/hr) 4 lanes, 800 veh/hr/ln 30 mph 40 mph 50 mph

85 Figure 24. Simulation-estimated added delay for a new development (no left-turn lane scenario). To facilitate the evaluations, linear regression was used to generate equations to represent the anticipated delay for different combinations of number of lanes, major-road volume, left-turn volume, and posted speed. In most cases the R2 value was greater than 0.8, which is not unexpected since this is modeling of microsimulation results. In a few cases the linear regression results in a negative delay reduction (i.e., delay increases because of the installation of a left-turn lane). This reflects the characteristic of linear regression and/or the stochastical nature of the simulation. For those situations, a minimum delay reduction of 0.01 sec/veh was assumed. The data for four lanes, 50 mph, 140 veh/hr turning left, and 600 or 800 veh/hr/ln on the major roadway were not included in the regression because those points were considered to be outliers. Table 45 lists the intercept terms and coefficients by number of lanes and speed limit for delay reduction for existing sites and delay generated due to new developments. Table 46 lists examples of the calculated delay for the two scenarios for 20, 60, 100, and 140 left-turn vehicles. 0 1 2 3 4 5 6 7 0 50 100 150 D ev el op m en t D el ay ( se c/ ve h) Left-Turn Volume (veh/hr) 2 lanes, 400 veh/hr/approach 30 mph 40 mph 50 mph 0 5 10 15 20 25 30 35 40 45 0 50 100 150 D ev el op m en t D el ay ( se c/ ve h) Left-Turn Volume (veh/hr) 4 lanes, 400 veh/hr/ln 30 mph 40 mph 50 mph 0 1 2 3 4 5 6 7 0 50 100 150 D ev el op m en t D el ay ( se c/ ve h) Left-Turn Volume (veh/hr) 2 lanes, 600 veh/hr/approach 30 mph 40 mph 50 mph 0 5 10 15 20 25 30 35 40 45 0 50 100 150 D ev el op m en t D el ay ( se c/ ve h) Left-Turn Volume (veh/hr) 4 lanes, 600 veh/hr/ln 30 mph 40 mph 50 mph 0 1 2 3 4 5 6 7 0 50 100 150 D ev el op m en t D el ay ( se c/ ve h) Left-Turn Volume (veh/hr) 2 lanes, 800 veh/hr/approach 30 mph 40 mph 50 mph 0 5 10 15 20 25 30 35 40 45 0 20 40 60 80 100 120 140 160D ev el op m en t D el ay (s ec /v eh ) Left-Turn Volume (veh/hr) 4 lanes, 800 veh/hr/ln 30 mph 40 mph 50 mph

86 Table 45. Regression coefficients to predict the delay determined from simulation. Number of Lanes Speed Limit (mph) Delay Reduction When Adding a Left-Turn Lane to an Existing Site Coefficients Delay Due to New Development Coefficients Intercept Major Volume Left-Turn Volume Intercept Major Volume Left-Turn Volume 2 30 −2.10008 0.00412 0.01423 −1.97700 0.00695 0.01532 40 −2.30383 0.00395 0.01289 −2.29792 0.00499 0.01675 50 −2.52283 0.00411 0.01373 −2.68758 0.00482 0.01860 4 30 −1.37877 0.00239 0.00766 −2.41700 0.00563 0.01490 40 −2.34039 0.00360 0.00965 −2.90076 0.00530 0.01927 50 −3.61735 0.00582 0.01407 −5.46192 0.00881 0.02988 Table 46. Predicted delays. Number of Lanes Speed Limit (mph) Major Volume (veh/hr/ ln) Delay a Reduction (sec/veh) When Adding a Left-Turn Lane to an Existing Site for Left-Turn Volume (veh/hr) of: Delay a (sec/veh) due to New Development for Left-Turn Volume (veh/hr) of: 20 60 100 140 20 60 100 140 2 30 400 0.0 0.4 1.0 1.5 1.1 1.7 2.3 2.9 600 0.7 1.2 1.8 2.4 2.5 3.1 3.7 4.3 800 1.5 2.0 2.6 3.2 3.9 4.5 5.1 5.7 40 400 0.0 0.0 0.6 1.1 0.0 0.7 1.4 2.0 600 0.3 0.8 1.4 1.9 1.0 1.7 2.4 3.0 800 1.1 1.6 2.1 2.7 2.0 2.7 3.4 4.0 50 400 0.0 0.0 0.5 1.0 0.0 0.4 1.1 1.8 600 0.2 0.8 1.3 1.9 0.6 1.3 2.1 2.8 800 1.0 1.6 2.1 2.7 1.5 2.3 3.0 3.8 4 30 400 0.0 0.0 0.3 0.6 0.1 0.7 1.3 1.9 600 0.2 0.5 0.8 1.1 1.3 1.9 2.4 3.0 800 0.7 1.0 1.3 1.6 2.4 3.0 3.6 4.2 40 400 0.0 0.0 0.1 0.5 0.0 0.4 1.1 1.9 600 0.0 0.4 0.8 1.2 0.7 1.4 2.2 3.0 800 0.7 1.1 1.5 1.9 1.7 2.5 3.3 4.0 50 400 0.0 0.0 0.1 0.7 0.0 0.0 1.1 2.2 600 0.2 0.7 1.3 b 0.4 1.6 2.8 b 800 1.3 1.9 2.4 b 2.2 3.4 4.6 b a Delay is defined based upon all vehicles in the system microsimulation. b Beyond limit of regression, use value scaled from Figure 23 or Figure 24.

87 The following is an illustration of the use of the equation for delay reduction when there are 600 veh/hr/ln on the major roadway and 60 left-turning vehicles during the peak hour: DR2 ln, 40 mph = −2.30383 + 0.00395 MajorPHV + 0.01289 LTLPHV (23) DR2 ln, 40 mph = −2.30383 + 0.00395(600) + 0.01289(60) = 0.83957 Where: DR2 ln, 40 mph = delay reduction when adding a left-turn lane on a two-lane highway with a 40-mph posted speed limit (sec/veh), MajorPHV = major-road peak-hour volume (veh/hr/ln), and LTLPHV = left-turn lane peak-hour volume (veh/hr). The regression delay reduction equations (coefficients in Table 45) were generated to facilitate the development of benefit-cost ratios. The equations permit automating calculations within a spreadsheet, which results in the ability to test more scenarios in the determination of left-turn lane warrants. Delay for Entire Year The simulation provides predictions of delay per vehicle in the system. This value needs to be converted to delay at the intersection for the entire year. To perform the conversion, the assumed number of hours along with the percent of the ADT represented by each traffic period is needed. Table 47 provides the assumptions used to convert sec/vehicle delay into hours of delay for the year at the intersection. Travel Time Delay Savings The national congestion constants used in the 2009 Urban Mobility Report (78) are shown in Table 48. The values represent 2007 dollars. The value of person time used in the Urban Mobility Report is based on the value of time, rather than the average or prevailing wage rate. The average cost of time was assumed to be $15.47 per person hour for 2007. For the analyses in this report, researchers used the 2007 value of time at $15.47 as presented in the 2009 Annual Urban Mobility Report (78). The 2007 value of time was adjusted using the Consumer Price Index (CPI) for 2007 and 2009 available from the U.S. Bureau of Labor Statistics (81). The ratio of the 2009 to 2007 CPI value is 214.537 divided by 207.342, which is 1.03. The ratio 1.03 multiplied by $15.47 gives a 2009 value of time of $16.01. The value represents average cost of time per person. To convert to an average cost of time per vehicle, the cost of time per person is multiplied by the vehicle occupancy factor of 1.25 persons per vehicle. This gives an average cost of time per vehicle of $20.01.

88 Table 47. Factors used to convert sec/veh delay to hr/intersection delay for a year. Traffic Period Number of Hours in Weekday Number of Hours in Weekend Hours per Yeara Hourly Percent of ADT during Typical Weekdayb Hourly Percent of ADT during Typical Weekendc Typical Hourly Volume If AADT Is 1000 veh/day Weekday AM Peak Hour 2 0 522 10.0 0 100 Weekday PM Peak Hour 2 0 522 10.0 0 100 Weekday Off-Peak & Weekend Off- Peak and Peak 5 9 2243 6.1 6.1 61 Evening 7 7 2555 2.8 2.8 28 Night 8 8 2920 1.8 1.8 18 Total 24 24 8762 a Assume 52.1 weeks/year with 5 days being weekdays and 2 days being weekend days. b Hourly percent of traffic for given traffic period on a typical weekday c Hourly percent of traffic for given traffic period on a typical weekend Table 48. National congestion constants used in the 2009 Urban Mobility Report (78). Constant a Value Vehicle Occupancy Working Days Percent of Daily Travel in Peak Periods (6 to 10 AM and 3 to 7 PM) Average Cost of Time (2007) Commercial Vehicle Operating Cost (2007) 1.25 persons per vehicle 250 days per year 50 percent $15.47 per person hour b $102.12 per vehicle hour b, c a Source: 2009 Urban Mobility Report methodology, http://tti.tamu.edu/documents/mobility_report_2009_wappx.pdf b Adjusted annually using the Consumer Price Index c Adjusted periodically using industry cost and logistics data CRASHES Crash Prediction The predicted average crash frequency for an intersection can be determined from equations in the Highway Safety Manual (HSM) (77). These equations, called safety performance functions, are regression models for estimating the predicted average crash frequency of individual roadway segments or intersections for a set of specific base conditions. As discussed in the HSM, each SPF in the predictive method was developed with observed crash data for a set of similar sites. The SPFs, like all regression models, estimate the value of a dependent variable as a function of a set of independent variables. In the SPFs developed for the HSM, the dependent

89 variable estimated is the predicted average crash frequency for a roadway segment or intersection under base conditions, and the independent variables are the AADTs of the roadway segment or intersection legs (and, for roadway segments, the length of the roadway segment). The SPFs applicable to the rural conditions in this study are listed in Table 49. Table 50 shows the equations for urban and suburban intersections on arterials used in this evaluation. Table 51 list the definitions for the variables listed in Table 50. Table 52 lists the acceptable ranges for average annual daily traffic for each equation. These ADT ranges were not exceeded in the evaluations. Table 49. Safety performance functions for rural highways for total crashes. Number of Lanes Number of Legs Equation Two Three Nspf 2 ln, 3st = exp[−9.86 + 0.79 × ln(AADTmaj) + 0.49 × ln(AADTmin)] (24) Two Four Nspf 2 ln, 4st = exp[−8.56 + 0.60 × ln(AADTmaj) + 0.61 × ln(AADTmin)] (25) Four Three Nspf 4 ln, 3st = exp[−12.526 + 1.204 × ln(AADTmaj) + 0.236 × ln(AADTmin)] (26) Four Four Nspf 4 ln, 4st = exp[−10.008 + 0.848 × ln(AADTmaj) + 0.448 × ln(AADTmin)] (27) Where: Nspf 2 ln, 3st = estimate of intersection-related predicted average crash frequency for base conditions for a rural two-lane highway with three-leg stop-controlled intersections, Nspf 2 ln, 4st = estimate of intersection-related predicted average crash frequency for base conditions for a rural two-lane highway with four-leg stop-controlled intersections, Nspf 4 ln, 3st = estimate of intersection-related predicted average total crash frequency for base conditions for a rural four-lane highway with three-leg stop-controlled intersections, Nspf 4 ln, 4st = estimate of intersection-related predicted average total crash frequency for base conditions for a rural four-lane highway with four-leg stop-controlled intersections, AADTmaj = AADT (vehicles per day) on the major road, and AADTmin = AADT (vehicles per day) on the minor road.

90 Table 50. Safety performance functions for urban and suburban arterials for total crashes. No. of Legs Crash Type Equation Three Multiple Nspf U/S-MV, 3st = exp[−13.36 + 1.11 × ln(AADTmaj) + 0.41 × ln(AADTmin)] (28) Four Multiple Nspf U/S-MV, 4st = exp[−8.90 + 0.82 × ln(AADTmaj) + 0.25 × ln(AADTmin)] (29) Three Single Nspf U/S-SV, 3st = exp[−6.81 + 0.16 × ln(AADTmaj) + 0.51 × ln(AADTmin)] (30) Four Single Nspf U/S-SV, 4st = exp[−5.33 + 0.33 × ln(AADTmaj) + 0.12 × ln(AADTmin)] (31) Before Installation of Left-Turn Lane Three Multiple and Single Nspf U/S, 3st, M&S, bef = (Nspf U/S-MV, 3st + Nspf U/S-SV, 3st) (32) Four Multiple and Single Nspf U/S, 4st, M&S, bef = (Nspf U/S-MV, 4st + Nspf U/S-SV, 4st) (33) Three Ped Nspf U/S-Ped, 3st, bef = 0.021 × (Nspf U/S, 3st, M&S, bef) (34) Four Ped Nspf U/S-Ped, 4st, bef = 0.022 × (Nspf U/S, 4st, M&S, bef) (35) Three Bike Nspf U/S-Bike, 3st, bef = 0.016 × (Nspf U/S, 3st, M&S, bef) (36) Four Bike Nspf U/S-Bike, 4st, bef = 0.018 × (Nspf U/S, 4st, M&S, bef) (37) Three All Nspf U/S, 3st, bef = Nspf U/S, 3st, M&S, bef + Nspf U/S-Ped, 3st, bef + Nspf U/S-Bike, 3st, bef (38) Four All Nspf U/S, 4st, bef = Nspf U/S, 4st, M&S, bef + Nspf U/S-Ped, 4st, bef + Nspf U/S-Bike, 4st, bef (39) After Installation of Left-Turn Lane Three Multiple and Single Nspf U/S, 3st, M&S, aft = (Nspf U/S-MV, 3st + Nspf U/S-SV, 3st) × AMFLTL (40) Four Multiple and Single Nspf U/S, 4st, M&S, aft = (Nspf U/S-MV, 4st + Nspf U/S-SV, 4st) × AMFLTL (41) Three Ped Nspf U/S-Ped, 3st, aft = 0.021 × (Nspf U/S, 3st, M&S, aft) (42) Four Ped Nspf U/S-Ped, 4st, aft = 0.022 × (Nspf U/S, 4st, M&S, aft) (43) Three Bike Nspf U/S-Bike, 3st, aft = 0.016 × (Nspf U/S, 3st, M&S, aft) (44) Four Bike Nspf U/S-Bike, 4st, aft = 0.018 × (Nspf U/S, 4st, M&S, aft) (45) Three All Nspf U/S, 3st, aft = Nspf U/S, 3st, M&S, aft + Nspf U/S-Ped, 3st, aft + Nspf U/S-Bike, 3st, aft (46) Four All Nspf U/S, 4st, aft = Nspf U/S, 4st, M&S, aft + Nspf U/S-Ped, 4st, aft + Nspf U/S-Bike, 4st, aft (47) Crashes That Did Not Occur due to Left-Turn Lane Three “Savings” NU/S, 3st, pred-saved = Nspf U/S, 3st, bef − Nspf U/S, 3st, aft (48) Four “Savings” NU/S, 4st, pred-saved = Nspf U/S, 4st, bef − Nspf U/S, 4st, aft (49) Variable descriptions are in Table 51.

91 Table 51. Definitions for variables in Table 50. Nspf U/S-MV, 3st = estimate of multiple-vehicle predicted average crash frequency for base conditions for urban/suburban arterial with three-leg stop-controlled intersections. Nspf U/S-MV, 4st = estimate of multiple-vehicle predicted average crash frequency for base conditions for urban/suburban arterial with four-leg stop-controlled intersections. Nspf U/S-SV, 3st = estimate of single-vehicle predicted average crash frequency for base conditions for urban/suburban arterial with three-leg stop-controlled intersections. Nspf U/S-SV, 4st = estimate of single-vehicle predicted average crash frequency for base conditions for urban/suburban arterial with four-leg stop-controlled intersections. Nspf U/S, 3st, M&S, bef = estimate of multiple- and single-vehicle predicted average crash frequency for urban/suburban arterial with three-leg stop-controlled intersections before left-turn lane is installed. Nspf U/S, 4st, M&S, bef = estimate of multiple- and single-vehicle predicted average crash frequency for urban/suburban arterial with four-leg stop-controlled intersections before left-turn lane is installed. Nspf U/S-Ped, 3st, bef = estimate of pedestrian predicted average crash frequency for urban/suburban arterial with three-leg stop-controlled intersections before left-turn lane is installed. Nspf U/S-Ped, 4st, bef = estimate of pedestrian predicted average crash frequency for urban/suburban arterial with four-leg stop-controlled intersections before left-turn lane is installed. Nspf U/S-Bike, 3st, bef = estimate of bicycle predicted average crash frequency for urban/suburban arterial with three-leg stop-controlled intersections before left-turn lane is installed. Nspf U/S-Bike, 4st, bef = estimate of bicycle predicted average crash frequency for urban/suburban arterial with four-leg stop-controlled intersections before left-turn lane is installed. Nspf U/S, 3st, bef = estimate of predicted average crash frequency for urban/suburban arterial with three-leg stop-controlled intersections before left-turn lane is installed. Nspf U/S, 4st, bef = estimate of predicted average crash frequency for urban/suburban arterial with four-leg stop-controlled intersections before left-turn lane is installed. Nspf U/S, 3st, M&S, aft = estimate of multiple- and single-vehicle predicted average crash frequency for urban/suburban arterial with three-leg stop-controlled intersections after left-turn lane is installed. Nspf U/S, 4st, M&S, aft = estimate of multiple- and single-vehicle predicted average crash frequency for urban/suburban arterial with four-leg stop-controlled intersections after left-turn lane is installed. Nspf U/S-Ped, 3st, aft = estimate of pedestrian predicted average crash frequency for urban/suburban arterial with three-leg stop-controlled intersections after left-turn lane is installed. Nspf U/S-Ped, 4st, aft = estimate of pedestrian predicted average crash frequency for urban/suburban arterial with four-leg stop-controlled intersections after left-turn lane is installed. Nspf U/S-Bike, 3st, aft = estimate of bicycle predicted average crash frequency for urban/suburban arterial with three-leg stop-controlled intersections after left-turn lane is installed. Nspf U/S-Bike, 4st, aft = estimate of bicycle predicted average crash frequency for urban/suburban arterial with four-leg stop-controlled intersections after left-turn lane is installed. Nspf U/S, 3st, aft = estimate of predicted average crash frequency for urban/suburban arterial with three-leg stop-controlled intersections after left-turn lane is installed. Nspf U/S, 4st, aft = estimate of predicted average crash frequency for urban/suburban arterial with four-leg stop-controlled intersections after left-turn lane is installed. AMFLTL = accident modification factor for left-turn lane—use 0.67 for three-leg or 0.73 for four-leg intersection (treatment on one approach only). NU/S, 3st, pred-saved = estimate of predicted crash frequency for urban/suburban arterial with three-leg stop- controlled intersections that did not occur because of the installation of a left-turn lane. NU/S, 4st, pred-saved = estimate of predicted crash frequency for urban/suburban arterial with four-leg stop- controlled intersections that did not occur because of the installation of a left-turn lane. AADTmaj = AADT (vehicles per day) on the major road. AADTmin = AADT (vehicles per day) on the minor road.

92 Table 52. Minimum and maximum AADT for Highway Safety Manual equations. Intersection Characteristics Major Approach Minimum to Maximum AADT Minor Approach Minimum to Maximum AADT Rural Two-Lane Highway with Three-Leg Stop-Controlled Intersections 0 to 19,500 veh/day 0 to 4,300 veh/day Rural Two-Lane Highway with Four-Leg Stop-Controlled Intersections 0 to 14,700 veh/day 0 to 3,500 veh/day Rural Four-Lane Highway with Three-Leg Stop-Controlled Intersections 0 to 78,300 veh/day 0 to 23,000 veh/day Rural Four-Lane Highway with Four-Leg Stop-Controlled Intersections 0 to 78,300 veh/day 0 to 7,400 veh/day Urban and Suburban Arterial Intersections with Three-Leg Stop-Controlled Intersections 0 to 45,700 veh/day 0 to 9,300 veh/day Urban and Suburban Arterial Intersections with Four-Leg Stop-Controlled Intersections 0 to 46,800 veh/day 0 to 5,900 veh/day For rural conditions, different SPFs are provided for two-lane and four-lane highways and for three- and four-leg intersections. For urban and suburban arterials, prediction equations are provided for three-leg and four-leg intersections with either stop control on the minor-road approaches (used in this study) or with signal control (not used in this study). Separate urban and suburban prediction equations are not provided based on the number of lanes on the major-road approach. The type of roadway segments included in the development of the SPFs and adjustment factors for urban and suburban arterials include two-lane undivided highways, three- lane arterials with center TWLTL, four-lane undivided highways, four-lane divided highways, and five-lane arterials including a center TWLTL. The predicted average crash frequency for base conditions is adjusted using accident modification factors and a calibration factor to adjust for a particular geographical area (not used in this evaluation). An illustration of the predicted average crashes frequency is shown in Figure 25 for the different conditions considered in this evaluation. The graph shows the predicted crashes for a range of major-road volumes when the minor-road ADT is 2000 veh/day. The predicted number of crashes for intersections on rural four-lane highways and rural two-lane four-leg intersections is higher than the crash prediction for urban and suburban arterials. The crash prediction in this illustration for rural four-lane three-leg intersections is similar to urban and suburban three-leg intersections for a given major-road average daily traffic.

93 Figure 25. Illustration of predicted crash frequency using Highway Safety Manual equations. Accident Modification Factor The accident modification factor for left-turn lanes is available from the Highway Safety Manual (77). For this evaluation, the assumption was that the intersections had a stop sign on the minor approaches and that only one of the major-road approaches would be treated with a left-turn lane. The AMFs for both the rural two-lane and four-lane highway scenarios are: • 0.56 for a three-leg intersection and • 0.72 for a four-leg intersection. The AMFs for the urban and suburban scenarios are: • 0.67 for a three-leg intersection and • 0.73 for a four-leg intersection. Comparison of Crash Prediction and Total Crashes at Selected Field Study Sites Because of the newness of the Highway Safety Manual and the crash prediction approach, questions have been asked regarding the accuracy of the predictions. A detailed comparison between actual crashes for a given set of conditions and the prediction procedure is beyond the scope of this study. A general comparison, however, was developed for a subset of the field 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 0 2000 4000 6000 8000 10000 12000 14000 16000 To ta l C ra sh F re qu en cy ( cr as he s/ ye ar ) Major-Road Volume (veh/day) Minor Road ADT = 2000 veh/day Urban, 3 legs Urban, 4 legs Rural, 2 lanes, 3 legs Rural, 2 lanes, 4 legs Rural, 4 lanes, 3 legs Rural, 4 lanes, 4 legs

94 studies. Figure 26 illustrates the predicted average total crashes and actual total crashes (average based on 5 years of data) for a selection of the field study sites where crash data were available to the research team. While there are examples of overpredictions and underpredictions, overall the trend is as expected. Those sites with a higher number of actual crashes are also those sites with the higher predictions. Figure 26. Comparison between actual crashes and predicted crashes for a sample of field study sites. Volumes Used in Crash Prediction for Benefit-Cost Evaluations Assumptions used to determine the traffic volumes used in the evaluation include the following: • Traffic volumes in both directions of travel on the major road are the same. • Traffic volume is evenly distributed across the lanes. • The minor-road volume is two times the volume of left-turn volume for three-leg intersections. • The minor-road volume is four times the volume of left-turn volume for four-leg intersections. • At four-leg intersections, only one major-road approach has a left-turn lane. There is no crossing traffic between the minor-road legs. 2009 Value of a Statistical Life by Crash Severity In 2008, a memo was released by the U.S. Department of Transportation regarding the treatment of the economic value of a statistical life in developmental analyses (79). The memo “raises to $5.8 million the value of a statistical life to be used by analysts in the Department of Transportation when assessing the benefit of preventing fatalities.” 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 P re di ct ed T ot al C ra sh es /Y ea r Actual Total Crash/Year

95 This section describes the methodology researchers used to develop an estimate of the value of a statistical life (VSL) in 2009 dollars by crash severity. Researchers used the methodology documented in Council et al. (80) and subsequently implemented in the Highway Safety Manual. There are seven steps in the methodology that follows. Step 1: Estimate the 2008 VSL by Crash Severity and Compute Factors for Subsequent Steps A February 5, 2008, U.S. Department of Transportation (U.S. DOT) memorandum indicates: …the economic value of preventing a human fatality is $5.8 million…. In addition, we will, for the first time, require supplementary analyses at values for a statistical life higher and lower than $5.8 million. Specifically, analysts will prepare estimates based on assumptions of $3.2 million and $8.4 million for the value associated with each life saved (79). With this guidance, researchers used $5.8 million as the “mid-range” comprehensive societal cost in 2008 dollars (the date of the U.S. DOT memorandum). Researchers used a “low” value of $3.2 million and a “high” value of $8.4 million for the subsequent computations. The Highway Safety Manual (77) provides estimates of the human capital costs and comprehensive societal costs by crash severity in 2001 dollars. These values are shown in Table 53. The fourth and fifth columns of Table 53 show factors used in subsequent computations. Table 53. Human capital cost and comprehensive societal cost from the Highway Safety Manual with factors for subsequent analyses. Crash Severity a Human Capital Cost b (2001 Dollars) Comprehensive Societal Cost b (2001 Dollars) Comprehensive Societal Cost for a Given Crash Severity Relative to a Fatalityc Comprehensive Societal Cost Relative to Human Capital Costd Fatality (K) $1,245,600 $4,008,900 1.0000 3.2184 Disabling Injury (A) $111,400 $216,000 0.0539 1.9390 Evident Injury (B) $41,900 $79,000 0.0197 1.8854 Possible Injury (C) $28,400 $44,900 0.0112 1.5810 PDO $6,400 $7,400 0.0018 1.1563 a2001 dollars as adapted from the Highway Safety Manual (77) bFrom Table 4A-1, “Crash Costs Estimates by Crash Severity,” from the Highway Safety Manual (77) cFor example, for a disabling injury (A), computed as $216,000 divided by $4,008,900 dFor example, for a disabling injury (A), computed as $216,000 divided by $111,400 Step 2: Estimate 2008 Comprehensive Societal Cost from U.S. DOT Memorandum Using Factors Developed in Step 1 Table 54 shows the low, mid-range, and high comprehensive societal cost of a fatality based on the U.S. DOT memorandum identified in Step 1. Costs by crash severity are computed with the “Comprehensive Societal Cost for a Given Crash Severity Relative to a Fatality” values shown in

96 Table 53. For example, the low disabling injury (A) comprehensive societal cost is computed as $3,200,000 multiplied by 0.0539 (from Table 53), which gives $172,400. Table 54. Low, mid-range, and high comprehensive societal cost estimates (2008 dollars). Crash Severity Comprehensive Societal Cost (Low) Comprehensive Societal Cost (Mid-range) Comprehensive Societal Cost (High) Fatality (K) $3,200,000 $5,800,000 $8,400,000 Disabling Injury (A) $172,400 $312,500 $452,600 Evident Injury (B) $63,100 $114,300 $165,500 Possible Injury (C) $35,800 $65,000 $94,100 PDO $5,900 $10,700 $15,500 Note: Values are rounded after spreadsheet calculations. Step 3: Estimate 2008 Human Capital Costs Using Factors Developed in Step 1 Researchers estimated the human capital costs by crash severity using the factors in the fifth column of Table 53. The factors in Table 53 (comprehensive societal cost relative to human capital cost factors) are the ratio of the comprehensive societal cost to the human capital cost. The low fatality (K) human capital cost is computed as $3,200,000 (from Table 54) divided by 3.2184 (from Table 53), which gives $994,300. The other values in Table 55 are computed in a similar manner. Table 55. Low, mid-range, and high human capital cost estimates (2008 dollars). Crash Severity Human Capital Cost (Low) Human Capital Cost (Mid-range) Human Capital Cost (High) Fatality (K) $994,300 $1,802,100 $2,610,000 Disabling Injury (A) $88,900 $161,200 $233,400 Evident Injury (B) $33,400 $60,600 $87,800 Possible Injury (C) $22,700 $41,100 $59,500 PDO $5,100 $9,300 $13,400 Note: Values are rounded after spreadsheet calculations. Step 4: Estimate Cost Difference between Comprehensive Societal Cost Estimates and Human Capital Cost by Crash Severity In this step, researchers computed the difference between the comprehensive societal cost estimates in Table 54 and the human capital cost estimates in Table 55. These values are shown in Table 56. For example the mid-range cost difference of $1,400 in Table 56 for PDO was determined as $10,700 (in Table 54) minus $9,300 (in Table 55).

97 Table 56. Cost difference between comprehensive societal cost estimates and human capital cost estimates (2008 dollars). Crash Severity Cost Difference (Low) Cost Difference (Mid-range) Cost Difference (High) Fatality (K) $2,205,700 $3,997,900 $5,790,000 Disabling Injury (A) $83,500 $151,300 $219,200 Evident Injury (B) $29,600 $53,700 $77,700 Possible Injury (C) $13,200 $23,900 $34,600 PDO $800 $1,400 $2,100 Note: Values are rounded after spreadsheet calculations. Step 5: Estimate the 2009 Human Cost by Crash Severity Researchers adjusted the 2008 human capital cost estimates using the CPI. From the U.S. Bureau of Labor Statistics, the CPI for 2008 is 215.303, and the CPI for 2009 is 214.537 (81). The ratio of the 2009 CPI to the 2008 CPI value (214.537 ÷ 215.303) is 0.996. Researchers multiplied the values in Table 55 by 0.996 to obtain the 2009 CPI-adjusted human capital cost estimates in Table 57. Table 57. 2009 CPI-adjusted human capital cost estimates (2009 dollars). Crash Severity Human Capital Cost (Low) Human Capital Cost (Mid-range) Human Capital Cost (High) Fatality (K) $990,700 $1,795,700 $2,600,700 Disabling Injury (A) $88,600 $160,600 $232,600 Evident Injury (B) $33,300 $60,400 $87,500 Possible Injury (C) $22,600 $40,900 $59,300 PDO $5,100 $9,200 $13,400 Note: Values are rounded after spreadsheet calculations. Step 6: Estimate the 2009 Cost Difference between Comprehensive Societal Cost and Human Capital Cost by Crash Severity Researchers adjusted the 2008 cost differences in Table 56 to 2009 dollars using the employment cost index (ECI). Researchers obtained quarterly ECI values from the U.S. Bureau of Labor Statistics (82). The quarterly values were averaged to obtain an annual value for 2008 (108.65) and 2009 (110.5). The ratio of the 2009 value to the 2008 value (110.5 ÷ 108.65) is 1.02. Researchers multiplied the values in Table 56 by 1.02 to obtain the 2009 ECI-adjusted cost differences by crash severity as shown in Table 58.

98 Table 58. 2009 ECI-adjusted cost difference between comprehensive societal cost estimates and human capital cost estimates (2009 dollars). Crash Severity Cost Difference (Low) Cost Difference (Mid-range) Cost Difference (High) Fatality (K) $2,243,300 $4,066,000 $5,888,600 Disabling Injury (A) $84,900 $153,900 $222,900 Evident Injury (B) $30,100 $54,600 $79,100 Possible Injury (C) $13,400 $24,300 $35,200 PDO $800 $1,500 $2,100 Note: Values are rounded after spreadsheet calculations. Step 7: Estimate 2009 Comprehensive Societal Cost Estimates Researchers estimated the 2009 total comprehensive societal costs by summing the 2009 human capital cost estimates (Table 57) and the 2009 cost differences (Table 58). This sum is shown in Table 59. Table 59. 2009 Comprehensive societal cost estimates (2009 dollars). Crash Severity Comprehensive Societal Cost (Low) Comprehensive Societal Cost (Mid-range) Comprehensive Societal Cost (High) Fatality (K) $3,234,000 $5,861,700 $8,489,300 Disabling Injury (A) $173,500 $314,500 $455,500 Evident Injury (B) $63,400 $115,000 $166,500 Possible Injury (C) $36,000 $65,200 $94,500 PDO $5,900 $10,700 $15,500 Note: Values are rounded after spreadsheet calculations. Typical Crash Cost for Three-Leg and Four-Leg Intersections The cost per crash at a three-leg or a four-leg intersection requires knowing the distribution of crash severity for the different intersection configurations. Table 10-5 in the Highway Safety Manual (77) provides the default proportions for crash severity levels for three-leg and four-leg stop-controlled rural intersections (reproduced as Table 60 in this report). Also needed is the conversion of the cost per person to a cost per crash. The number of individuals killed or injured in a crash is not readily available. A study on red-light running at signalized intersections in Texas identified the number of annual crashes and the number of annual injuries by severity level (83). From those values, the number of injuries or fatalities can be calculated as shown in Table 61.

99 Table 60. Default distribution of crash severity level at rural two-lane two-way intersections from the Highway Safety Manual (77). Crash Severity Level Percentage of Total Crashes Three-Leg Stop- Controlled Intersections Four-Leg Stop- Controlled Intersections Four-Leg Signalized Intersections Fatality Incapacitating Injury Nonincapacitating Injury Possible Injury Property Damage Only 1.7 4.0 16.6 19.2 58.5 1.8 4.3 16.2 20.8 56.9 0.9 2.1 10.5 20.5 66.0 Total 100.0 100.0 100.0 Table 61. Injuries per crash for red-light-running crashes (83). Severity Annual Crashes Annual Injuries or Deaths Injuries or Deaths/Crash K 121 133 1.10 deaths/crash A 1,439 2,047 1.42 injuries/crash B 5,493 8,987 1.64 injuries/crash C 11,798 24,802 2.10 injuries/crash PDO 18,851 0 0.00 injuries/crash A current Texas Department of Transportation (TxDOT) study is examining crashes at rural intersections. Data available for 595 rural intersections provided the distributions shown in Table 62. For the 1198 crashes, the number of injured persons per crash ranged between 1.22 and 2.30. The fatal crashes had 1.09 deaths per crash at the four-leg intersections and 1.46 deaths per crash at the three-leg intersections. Reflecting the multiple conflict points at an intersection, the average number of vehicles involved at a crash ranged between 1.48 and 2.36 veh/crash. Table 63 and Table 64 show the calculations to determine typical crash cost using the ranges for comprehensive societal cost for three-leg and four-leg rural highway intersections, respectively. The calculations to determine typical costs for urban suburban arterials are shown in Table 65. The Highway Safety Manual also provides crash cost estimates by crash severity. These values are listed in Table 66. The crash costs listed in Table 66 were converted to 2009 dollars, and then the typical crash costs by number of legs and rural or urban were determined (see Table 67). The values in Table 66 are costs per crash, while the previous calculations had to convert the cost for a statistical life into cost per crash. The crash cost values in the Highway Safety Manual are assumed to already have accounted for the number of persons typically involved in a crash along with the distribution of injuries within a crash. The HSM values, however, do not account for the higher value being placed on a statistical life. Therefore, most of the B/C calculations were performed using the values listed in Table 63, Table 64, and Table 65. A comparison is made, however, at the end of this section with the left-turn lane warrants that would result if the costs in Table 67 are assumed.

100 Table 62. Injuries or deaths per crash for rural intersections. Severity a Injuries or Deaths/Crash Number of Persons/Crash Number of Vehicles/Crash Three Legs Four Legs Three Legs Four Legs Three Legs Four Legs K 1.46 deaths/crash 0.31 A injuries/crash 1.15 B injuries/crash 0.00 C injuries/crash 0.31 no injuries/crash 0.15 unk. injuries/crash 1.09 deaths/crash 0.55 A injuries/crash 0.55 B injuries/crash 0.36 C injuries/crash 0.36 no injuries/crash 0.36 unk. injuries/crash 3.38 3.27 1.54 2.36 A 1.17 A injuries/crash 0.29 B injuries/crash 0.12 C injuries/crash 0.38 no injuries/crash 0.06 unk. injuries/crash 1.40 A injuries/crash 0.47 B injuries/crash 0.43 C injuries/crash 1.83 no injuries/crash 0.10 unk. injuries/crash 2.01 4.23 1.48 2.00 B 1.30 B injuries/crash 0.18 C injuries/crash 0.59 no injuries/crash 0.09 unk. injuries/crash 1.42 B injuries/crash 0.48 C injuries/crash 1.08 no injuries/crash 0.08 unk. injuries/crash 2.15 3.06 1.55 1.87 C 1.22 C injuries/crash 0.89 no injuries/crash 0.13 unk. injuries/crash 1.34 C injuries/crash 1.20 no injuries/crash 0.09 unk. injuries/crash 2.24 2.64 1.53 1.82 PDO 0.00 injuries/crash 0.00 injuries/crash 2.15 2.48 1.61 1.88 a Findings based on 1189 crashes at 595 rural Texas intersections for the time period of 2003 to 2008 Unk. = unknown

101 Table 63. Typical crash cost calculations for three-leg rural intersections. R an ge (C os t) Crash Severity Injury Severity Cost a, b Convert Cost/Person to Cost/Crash c Cost per Crash Percent of Total Crashes d Extension M id -r an ge ($ 21 4, 00 0) Fatality K A B C $5,861,700 $314,500 $115,000 $65,200 1.46 0.31 1.15 0.00 $8,558,082 $97,495 $132,250 $0 1.70 $149,393 A A B C $314,500 $115,000 $65,200 1.17 0.29 0.12 $367,965 $33,350 $7,824 4.00 $16,366 B B C $115,000 $65,200 1.30 0.18 $149,500 $11,736 16.60 $26,765 C C $65,200 1.22 $79,544 19.20 $15,272 PDO PDO $10,700 1.00 e $10,700 58.50 $6,260 Total (cost/crash) 100.00 $214,056 Lo w ($ 11 8, 00 0) Fatality K A B C $3,234,000 $173,500 $63,400 $36,000 1.46 0.31 1.15 0.00 $4,721,640 $35,785 $72,910 $0 1.70 $82,422 A A B C $173,500 $63,400 $36,000 1.17 0.29 0.12 $202.995 $18,386 $4,320 4.00 $9,028 B B C $63,400 $36,000 1.30 0.18 $82,420 $6,480 16.60 $14,757 C C $36,000 1.22 $43,920 19.20 $8,433 PDO PDO $5,900 1.00 e $5,900 58.50 $3,452 Total (cost/crash) 100.00 $118,091 H ig h ($ 31 0, 00 0) Fatality K A B C $8,489,300 $455,500 $166,500 $94,500 1.46 0.31 1.15 0.00 $12,394,378 $141,205 $191,475 $0 1.70 $216,360 A A B C $455,500 $166,500 $94,500 1.17 0.29 0.12 $532,935 $48,285 $11,340 4.00 $23,702 B B C $166,500 $94,500 1.30 0.18 $216,450 $17,010 16.60 $28,754 C C $94,500 1.22 $115,290 19.20 $22,136 PDO PDO $15,500 1.00 e $15,500 58.50 $9,068 Total (cost/crash) 100.00 $310,020 a Comprehensive societal cost for fatal crash is from “Treatment of the Economic Value of a Statistical Life in Departmental Analyses,” Memorandum to Secretarial Officers, Modal Administrators, available at http://ostpxweb.dot.gov/policy/reports/080205.htm. b Comprehensive societal cost for crash severity A, B, C, or PDO is based on distribution determined using Highway Safety Manual data (see Table 53), with costs adjusted to 2009 dollars. c Factors from Table 62 d From Table 10-5 of the Highway Safety Manual (77) e No factor is needed. Assumption is that cost reflects cost per crash.

102 Table 64. Typical crash cost calculations for four-leg intersections. R an ge (C os t) Crash Severity Injury Severity Cost a, b Convert Cost/Person to Cost/Crash c Cost per Crash Percent of Total Crashes d Extension M id -r an ge ($ 19 8, 00 0) Fatality K A B C $5,861,700 $314,500 $115,000 $65,200 1.09 0.55 0.55 0.36 $6,389,253 $172,975 $63,250 $23,472 1.80 $119,681 A A B C $314,500 $115,000 $65,200 1.40 0.47 0.43 $440,300 $54,050 $28,036 4.30 $22,463 B B C $115,000 $65,200 1.42 0.48 $163,300 $31,296 16.20 $31,525 C C $65,200 1.34 $87,368 20.80 $18,173 PDO PDO $10,700 1.00 e $10,700 56.90 $6,088 Total (cost/crash) 100.00 $197,929 Lo w ($ 10 9, 00 0) Fatality K A B C $3,234,000 $173,500 $63,400 $36,000 1.09 0.55 0.55 0.36 $3,525,060 $95,425 $34,870 $12,960 1.80 $66,030 A A B C $173,500 $63,400 $36,000 1.40 0.47 0.43 $242,900 $29,798 $15,480 4.30 $12,392 B B C $63,400 $36,000 1.42 0.48 $90,028 $17,280 16.20 $17,384 C C $36,000 1.34 $48,240 20.80 $10,034 PDO PDO $5,900 1.00 e $5,900 56.90 $3,357 Total (cost/crash) 100.00 $109,196 H ig h ($ 28 7, 00 0) Fatality K A B C $8,489,300 $455,500 $166,500 $94,500 1.09 0.55 0.55 0.36 $9,253,337 $250,525 $91,575 $34,020 1.80 $173,330 A A B C $455,500 $166,500 $94,500 1.40 0.47 0.43 $637,700 $78,255 $40,635 4.30 $32,522 B B C $166,500 $94,500 1.42 0.48 $236,420 $45,360 16.20 $45,650 C C $94,500 1.34 $126,630 20.80 $26,339 PDO PDO $15,500 1.00 e $15,500 56.90 $8,820 Total (cost/crash) 100.00 $286,672 a Comprehensive societal cost for fatal crash is from “Treatment of the Economic Value of a Statistical Life in Departmental Analyses,” Memorandum to Secretarial Officers, Modal Administrators, available at http://ostpxweb.dot.gov/policy/reports/080205.htm. b Comprehensive societal cost for crash severity A, B, C, or PDO is based on distribution determined using Highway Safety Manual data (see Table 53), with costs adjusted to 2009 dollars. c Factors from Table 62 d From Table 10-5 of the Highway Safety Manual (77) e No factor is needed. Assumption is that cost reflects cost per crash.

103 Table 65. Typical crash cost calculations for urban and suburban intersections. Range (Cost) Crash Severity Cost a, b Convert Cost/ Person to Cost/ Crash c Cost per Crash Percent of Total Crashes for Three Leg d Extension for Three Legs Percent of Total Crashes for Four Legs d Extension for Four Legs Mid- range Fatality $5,861,700 1.10 $6,447,870 1.47 $95,087 1.60 $103,405 A $314,500 1.42 $446,590 3.47 $15,496 3.83 $17,109 B $115,000 1.64 $188,600 14.40 $27,158 14.43 $27,221 C $65,200 2.10 $136,920 16.66 $22,805 18.53 $25,374 PDO $10,700 1.00 e $10,700 64.00 $6,848 61.60 $6,591 Total (cost/crash) $167,394 $179,701 Rounded total (cost/crash) $167,000 $180,000 Low Fatality $3,234,000 1.10 $3,557,400 1.47 $52,461 1.60 $57,050 A $173,500 1.42 $246,370 3.47 $8,549 3.83 $9,439 B $63,400 1.64 $103,976 14.40 $14,973 14.43 $15,007 C $36,000 2.10 $75,600 16.66 $12,591 18.53 $14,010 PDO $5,900 1.00 e $5,900 64.00 $3,776 61.60 $3,634 Total (cost/crash) $92,350 $99,141 Rounded total (cost/crash) $92,000 $99,000 High Fatality $8,489,300 1.10 $9,338,230 1.47 $137,711 1.60 $149,758 A $455,500 1.42 $646,810 3.47 $22,444 3.83 $24,780 B $166,500 1.64 $273,060 14.40 $39,321 14.43 $39,412 C $94,500 2.10 $198,450 16.66 $33,053 18.53 $36,776 PDO $15,500 1.00 e $15,500 64.00 $9,920 61.60 $9,548 Total (cost/crash) $242,448 $260,274 Rounded total (cost/crash) $242,000 $260,000 a Comprehensive societal cost for fatal crash is from “Treatment of the Economic Value of a Statistical Life in Departmental Analyses,” Memorandum to Secretarial Officers, Modal Administrators, available at http://ostpxweb.dot.gov/policy/reports/080205.htm. b Comprehensive societal cost for crash severity A, B, C, or PDO is based on distribution determined using Highway Safety Manual data (see Table 53), with costs adjusted to 2009 dollars. c Factors from Table 61 d Table 52 from Methodology to Predict the Safety Performance of Urban and Suburban Arterials (84) shows PDO crashes to be 64.0 percent for multiple-vehicle crashes at three-leg stop-controlled intersections and 61.6 percent for four-leg stop-controlled intersections. The remaining 36.0 percent for three-leg and 38.4 percent for four-leg intersections were distributed between fatality, A, B, and C using similar proportions as assumed for rural highways. e No factor is needed. Assumption is that cost reflects cost per crash. Table 66. Crash cost estimates by crash severity from the Highway Safety Manual (77). Crash Severity Level Human Capital Crash Costs (2001 Dollars) Comprehensive Crash Costs (2001 Dollars) Fatality Incapacitating Injury Nonincapacitating Injury Possible Injury Property Damage Only $1,245,600 $111,400 $41,900 $28,400 $6,400 $4,008,900 $216,000 $79,000 $44,900 $7,400 Source: references within the Highway Safety Manual to Council et al., Crash Cost Estimates by Maximum Police-Reported Injury Severity within Selected Crash Geometries, FHWA-HRT-05-051, October 2005.

104 Table 67. Typical crash cost by number of legs and rural or urban based on Highway Safety Manual crash costs. Crash Severity Level Comprehensive Crash Costs a (2009 Dollars) Rural Urban and Suburban 3 Legs 4 Legs 3 Legs 4 Legs Crash Severity Distribution Fatality (K) $5,059,425 1.7 1.8 1.5 1.6 Disabling Injury (A) $269,348 4.0 4.3 3.5 3.8 Evident Injury (B) $98,426 16.6 16.2 14.4 14.4 Possible Injury (C) $55,604 19.2 20.8 16.7 18.5 PDO (O) $9,038 58.5 56.9 64.0 61.6 Typical Crash Cost Typical Crash Cost per Number of Legs and Rural or Urban Based on HSM Data $129,086 $135,305 $112,941 $121,340 a Comprehensive crash cost for crash severity from Highway Safety Manual Table 4A-1 adjusted to 2009 dollars CONSTRUCTION COSTS Typical construction costs for left-turn lanes were identified from several sources. Construction costs were identified in two documents. The FHWA study on safety effectiveness of turn lanes by Harwood et al. (2) used an average of $85,000 to be the cost associated with installing a left- turn lane, based on estimates from four of the states that participated in that study. The value of $100,000 was assumed as the cost for constructing a right-turn lane in the Potts et al. (58) work. The amount was selected as “a reasonable value that would be substantial to require in-depth analysis but not overly cost-prohibitive.” Based on the date of their reports, it is assumed to represent 2005 dollars. Table 68 lists the estimated costs identified in the literature along with the equivalent 2009 dollar values using the Consumer Price Index (81). State department of transportation websites were also searched for information on bids for letting a left-turn lane project. Table 69 lists a compilation of recently let (2009 or 2010) projects that involved installation of a left-turn lane. Data from the following four states were obtained: Texas (85), Louisiana (86), Ohio (87), and Florida (88). A reasonable range for the cost of constructing a left-turn lane appears to be $100,000 to $375,000 with an average value of $250,000. These values are used to represent the following range listed in the evaluation: • $100,000 to represent minimal (min) costs, • $250,000 to represent moderate (mod) costs, and • $375,000 to represent maximum (max) costs within the range studied in this evaluation.

105 Table 68. Estimated construction cost from literature. Study Estimated Construction Cost for Turn Lane ($1,000) Assumed Year of Cost Consumer Price Index for Year of Estimate Consumer Price Index for 2009 Construction Cost in 2009 Dollars ($1,000) FHWA Safety of Turn Lanes (2) 85 2001 177.1 214.537 103 Right-Turn Lane (58) 100 2005 195.3 214.537 110 Table 69. Construction cost for left-turn lane projects from four states. State Let Date Highway County Cost ($1,000) Texas December 2009 SH 95 Bastrop 250 Texas December 2009 SH 95 Bastrop 120 Texas December 2009 SH 95 Bastrop 250 Texas April 2010 US 281 Blanco 200 Texas April 2010 US 281 Blanco 250 Texas April 2010 US 281 Blanco 140 Texas April 2010 SH 29 Burnet 345 Texas March 2010 FM 969 Travis 180 Texas March 2010 FM 969 Travis 280 Texas March 2010 FM 1327 Travis 320 Texas July 2010 RM 1431 Travis 393 Texas May 2010 US 183 Travis 400 Texas May 2010 US 183 Travis 170 Texas Rounded average 254 Louisiana July 2010 LA 22 Ascension 750 a Louisiana October 2010 US 71 Bossier 375 b Louisiana August 2010 LA 428 Orleans 375 b Louisiana August 2010 LA 594 Ouachita 375 b Louisiana June 2010 US 90 St. Charles 375 b Louisiana July 2010 LA 22 Tangipahoa 175 c Louisiana November 2010 LA 10 Washington 175 c Louisiana Rounded average 371 Ohio November 2010 SR 78 Woodsfield 155 Ohio Rounded average 155 Florida October 2009 333312-1-52-07 223 Florida October 2009 333324-1-52-07 292 Florida October 2009 333325-1-52-07 250 Florida Rounded average 255 Rounded average for projects listed in table 250 a Represents middle of estimated range of $500,000 to $1,000,000 b Represents middle of estimated range of $250,000 to $500,000 c Represents middle of estimated range of $100,000 to $250,000

106 EXAMPLES OF CALCULATIONS FOR ADDING LEFT-TURN LANE AT EXISTING SITE Adding Left-Turn Lane at Existing Site on Rural Two-Lane Highway Annual Delay Savings The following illustrates the calculations to determine if a left-turn lane should be considered at a rural two-lane highway site. Assume that the conditions at the site include the following: • Two lanes, • Rural location, • Three legs, • 50-mph posted speed limit, • 450 veh/hr/ln in the peak hour (10,000 ADT on the major road), • 100 veh/hr turning left in the peak hour, and • 2000 ADT on the minor road. The amount of expected delay reduction that would be attributed to the left-turn lane during the peak hour is 0.701 sec/veh. This value was determined using the regression coefficients listed in Table 45; however, it could also be determined from Figure 23. The delay reduction represents the per-vehicle delay savings. To determine the savings for all the vehicles at the intersection for that hour, the delay reduction value needs to be multiplied by the number of vehicles at the intersection for that hour, in this example 1000 veh (450 through and right-turning vehicles per lane on each approach along with 100 left-turning veh). Therefore 701 sec of delay was reduced during the AM peak hour. With 522 hours in that traffic period, the amount of delay savings for the year is 102 hours. The amount of delay savings per traffic period is shown in Table 70. For this site, the annual delay saving is $4,214 assuming a per-hour vehicle cost of $20.01. Annual Crash Savings The determination of the savings attributed to crashes begins with calculating the predicted number of crashes for the intersection. The equation for a three-leg intersection is: Nspf 2 ln, 3st = exp[−9.86 + 0.79 × ln(AADTmaj) + 0.49 × ln(AADTmin)] (50) Nspf 2 ln, 3st = exp[−9.86 + 0.79 × ln(10,000) + 0.49 × ln(2000)] Nspf 2 ln, 3st = 3.13 crashes/year

107 Table 70. Calculation of annual delay savings for rural two-lane highway example. Traffic Period Hourly Factor Hours/ Year VTR (veh/ hr) VLT (veh/ hr) DR (sec/ veh) DR (sec) in the Hour DR (sec/Year) DR (hr/Year) AM Peak 10 522 450 100 0.701 701.1 36,5987 101.66 PM Peak 10 522 450 100 0.701 701.1 36,5987 101.66 Off Peak/ Weekend Peak 6.1 2243 274.5 61 0.010 6.1 13,682 3.80 Evening 2.8 2555 126 28 0.010 2.8 7,154 1.99 Night 1.8 2920 81 18 0.010 1.8 5,256 1.46 Total 210.57 Dollars per Vehicle Hour Cost $20.01 Annual Delay Savings $4,213.59 VTR = Through and right-turn volume on major approach VLT = Left-turn volume DR = Delay reduction The accident modification factor for adding a left-turn lane on one approach for a three-leg intersection is 0.56. The reduction in number of crashes at the intersection can be determined as follows: Nspf 2 ln, 3st − w/LTL = Nspf 2 ln, 3st (AMFLTL) = 3.13 (0.56) = 1.75 crashes/year (51) Nspf 2 ln, 3st − savings due LTL = Nspf 2 ln, 3st − Nspf 2 ln, 3st − w/LTL = 3.13 – 1.75 = 1.38 crashes/year (52) The costs per crash at three-leg intersections are: • $214,000 (average), • $118,000 (low range), and • $310,000 (high range). Multiplying the cost per crash by the number of crashes that would not occur due to the presence of the left-turn lane results in the following annual crash savings: • $294,596 (average), • $162,441 (low range), and • $426,752 (high range). Present Worth of Annual Savings and Benefit-Cost Ratio The delay and crash savings above represent the expected value per year. Assuming a 20-year design life and a 4 percent return, those annual savings need to be converted to a present worth so that the expected construction cost of the left-turn lane can be considered. The construction cost was estimated to be $250,000.

108 The B/C ratio when using the mid-range societal cost is: ஻ ஼ ൌ ଵଷ.ହଽ ൈ ሺ$ସ,ଶଵସ ା $ଶଽସ,ହଽ଺ሻ $ଶହ଴,଴଴଴ ൌ 16.2 (53) The B/C ratio of 16.2 indicates that the installation of a left-turn lane should be warranted for these conditions. Adding Left-Turn Lane on Existing Rural Four-Lane Highway Annual Delay Savings The following illustrates the calculations to determine if a left-turn lane should be considered at a rural four-lane highway site. Assume that the conditions at the site include the following:  Four lanes on the major road,  Rural highway,  Four legs,  30-mph posted speed limit,  350 veh/hr/ln in the peak hour (16,000 ADT on the major road),  100 veh/hr turning left in the peak hour, and  4,000 ADT on the minor road. The amount of expected delay reduction that would be attributed to the left-turn lane during the peak hour is 0.28 sec/veh. This value was determined using the regression coefficients; however, it could also be determined from Figure 23. The amount of delay savings per traffic period is shown in Table 71. For this site, the annual delay saving is $1,514 assuming a per-hour vehicle cost of $20.01. Annual Crash Savings The determination of the savings attributed to crashes begins with calculating the predicted number of crashes for the intersection. The equation for a three-leg intersection is: Nspf 4ln, 4st = exp[−10.01 + 0.85 × ln(AADTmaj) + 0.45 × ln(AADTmin)] (54) Nspf 4ln, 4st = exp[−10.01 + 0.85 × ln(16,000) + 0.49 × ln(4,000)] Nspf 4ln, 4st = 6.798 crashes/year

109 Table 71. Calculation of annual delay savings for rural four-lane highway example. Traffic Period Hourly Factor Hours/ Year VTR (veh/ hr/ln) VLT (veh/ hr) DR (sec/ veh) DR (sec/Year) DR (hr/Year) AM Peak 10 522 375 100 0.28 12,5107 34.75 PM Peak 10 522 375 100 0.28 12,5107 34.75 Off Peak/ Weekend Peak 6.1 2243 229 61 0.01 11,630 3.23 Evening 2.8 2555 105 28 0.01 6,081 1.69 Night 1.8 2920 68 18 0.01 4,468 1.24 Total 75.66 Dollars per Vehicle Hour Cost $20.01 Annual Delay Savings $1,514 VTR = Through and right-turn volume on major approach VLT = Left-turn volume DR = Delay reduction The accident modification factor for adding a left-turn lane on one approach for a four-leg intersection is 0.72. The reduction in number of crashes at the intersection can be determined as follows: Nspf 4 ln, 4st − w/LTL = Nspf 4 ln, 4st × (AMFLTL) = 6.798 × (0.72) = 4.895 crashes/year (55) Nspf 4 ln, 4st − savings due LTL = Nspf 4 ln, 4st − Nspf 4 ln, 4st − w/LTL = 6.798 – 4.895 = 1.904 crashes/year (56) The costs per crash at three-leg intersections are: • $198,000 (mid-range), • $109,000 (low range), and • $287,000 (high range). Multiplying the cost per crash by the number of crashes that would not occur due to the presence of the left-turn lane results in the following annual crash savings: • $376,895 (mid-range), • $207,483 (low range), and • $546,308 (high range). Present Worth of Annual Savings and Benefit-Cost Ratio The delay and crash savings above represent the expected value per year. Assuming a 20-year design life and a 4 percent return, those annual savings need to be converted to a present worth so that the expected construction cost of the left-turn lane can be considered. The construction cost was estimated to be $250,000.

110 The B/C ratio when using the mid-range societal cost is: ஻ ஼ ൌ ଵଷ.ହଽ ൈ ሺ$ଵ,ହଵସ ା $ଷ଻଺,଼ଽହሻ $ଶହ଴,଴଴଴ ൌ 20.6 (57) The B/C ratio of 20.6 indicates that the installation of a left-turn lane should be warranted for these conditions. Adding Left-Turn Lane to Existing Urban and Suburban Intersection Annual Delay Savings The following illustrates the calculations to determine if a left-turn lane should be considered at a site. Assume that the conditions at the site include the following:  Four lanes on the major road,  Urban arterial,  Three legs,  40-mph posted speed limit,  350 veh/hr/ln in the peak hour (14,000 ADT on the major road),  100 veh/hr turning left in the peak hour, and  4000 ADT on the minor road. The amount of expected delay reduction that would be attributed to the left-turn lane during the peak hour is 0.16 sec/veh. This value was determined using the regression coefficients; however, it could also be determined from Figure 23. The amount of delay savings per traffic period is shown in Table 72. For this site, the annual delay saving is $816 assuming a per-hour vehicle cost of $20.01. Table 72. Calculation of annual delay savings for urban and suburban example. Traffic Period Hourly Factor Hours/ Year VTR (veh/ hr) VLT (veh/ hr) DR (sec/ veh) DR (sec/Year) DR (hr/Year) AM Peak 10 522 325 100 0.16 63,663 17.68 PM Peak 10 522 325 100 0.16 63,663 17.68 Off Peak/ Weekend Peak 6.1 2243 198 61 0.01 10,262 2.85 Evening 2.8 2555 91 28 0.01 5,366 1.49 Night 1.8 2920 59 18 0.01 3,942 1.10 Total Hours/Year of Delay Reduction 40.80 Dollars per Vehicle Hour Cost $20.01 Annual Delay Savings $816.44 VTR = Through and right-turn volume on major approach VLT = Left-turn volume DR = Delay reduction

111 Annual Crash Savings The determination of the savings attributed to crashes begins with calculating the predicted number of crashes for the intersection. For urban or suburban intersections, the predicted number of crashes consists of the predicted number of multiple-vehicle crashes, predicted number of single-vehicle crashes, predicted number of pedestrian-vehicle crashes, and predicted number of bicycle-vehicle crashes both before and after a left-turn lane is installed. This study is interested in the number of crashes that did not occur due to the addition of the left-turn lane. The equations are shown in Table 50. Following is an illustration of the steps for this example: Nspf U/S-MV, 3st = exp[−13.36 + 1.11 × ln(AADTmaj) + 0.41 × ln(AADTmin)] (58) = exp[−13.36 + 1.11 × ln(14,000) + 0.41 × ln(4000)] = 1.89 multiple-vehicle crashes/year Nspf U/S-SV, 3st = exp[−6.81 + 0.16 × ln(AADTmaj) + 0.51 × ln(AADTmin)] (59) = exp[−6.81 + 0.16 × ln(14,000) + 0.51 × ln(4000)] = 0.35 single-vehicle crashes/year Nspf U/S, 3st, M&S, bef = (Nspf U/S-MV, 3st + Nspf U/S-SV, 3st) (60) = (1.89 + 0.35) = 2.24 crashes/year Nspf U/S-Ped, 3st, bef = 0.021 × (Nspf U/S, 3st, M&S, bef) (61) = 0.021 × (2.24) = 0.05 Nspf U/S-Bike, 3st, bef = 0.016 × (Nspf U/S, 3st, M&S, bef) (62) = 0.016 × (2.24) = 0.04 Nspf U/S, 3st, bef = Nspf U/S, 3st, M&S, bef + Nspf U/S-Ped, 3st, bef + Nspf U/S-Bike, 3st, bef (63) = 2.24 + 0.05 + 0.04 = 2.32 Nspf U/S, 3st, M&S, aft = (Nspf U/S-MV, 3st + Nspf U/S-SV, 3st) × AMFLTL (64) = (1.89 + 0.35) × 0.67 = 1.50 crashes/year Nspf U/S-Ped, 3st, aft = 0.021 × (Nspf U/S, 3st, M&S, aft) (65) = 0.021 × (1.50) = 0.03 Nspf U/S-Bike, 3st, aft = 0.016 × (Nspf U/S, 3st, M&S, aft) (66) = 0.016 × (1.50) = 0.02 Nspf U/S, 3st, aft = Nspf U/S, 3st, M&S, aft + Nspf U/S-Ped, 3st, aft + Nspf U/S-Bike, 3st, aft (67) = 1.50 + 0.03 + 0.02 = 1.56 NU/S, 3st, pred-saved = Nspf U/S, 3st, bef − Nspf U/S, 3st, aft (68) = 2.32 – 1.56 = 0.767 crashes not occurring/year

112 The costs per crash at three-leg urban and suburban intersections are:  $167,000 (mid-range),  $92,000 (low range), and  $242,000 (high range). Multiplying the cost per crash by the number of crashes that would not occur due to the presence of the left-turn lane results in the following annual crash savings:  $128,062 (average),  $70,549 (low range), and  $185,574 (high range). Present Worth of Annual Savings and Benefit-Cost Ratio The delay and crash savings above represent the expected value per year. Assuming a 20-year design life and a 4 percent return, those annual savings need to be converted to a present worth so that the expected construction cost of the left-turn lane can be considered. The construction cost was estimated to be $250,000. The B/C ratio when using the mid-range societal cost is: ஻ ஼ ൌ ଵଷ.ହଽ ൈ ሺ$଼ଵ଺ ା $ଵଶ଼,଴଺ଶሻ $ଶହ଴,଴଴଴ ൌ 7.0 (69) The B/C ratio of 7.0 indicates that the installation of a left-turn lane should be warranted for these conditions. GREEN BOOK WARRANTS FOR LEFT-TURN LANE Figure 27 shows a plot of the Green Book rural two-lane highway left-turn warrants in a graphical form that uses left-turn lane volume and average peak-hour major-road approach volume. The current Green Book warrant is based on percent left turns and uneven approach lane volumes, hence the multiple left-turn volume for a given major-road volume in Figure 27. For a simpler showing of the Green Book data in other graphs, lines representing a subset of the Green Book data were generated for each speed (see Figure 28).

113 Figure 27. Plot of Green Book rural two-lane highway left-turn warrant values. Figure 28. Lines generated to represent a subset of the Green Book rural two-lane highway left-turn warrant values. 0 20 40 60 80 100 120 0 100 200 300 400 500 600 P ea k- H ou r L ef t- Tu rn V ol um e (v eh /h r) Average Peak-Hour Major-Road Approach Volume (veh/hr/approach) 40 mph 50 mph 60 mph y = -0.1707x + 111.77 R² = 0.8625 y = -0.1299x + 86.964 R² = 0.7851 y = -0.1052x + 68.219 R² = 0.7901 0 20 40 60 80 100 0 100 200 300 400 500 600 P ea k- H ou r L ef t- Tu rn V ol um e (v eh /h r) Average Peak-Hour Major-Road Approach Volume (veh/hr/approach) 40 mph 50 mph 60 mph Linear (40 mph) Linear (50 mph) Linear (60 mph)

114 DEVELOP PRELIMINARY WARRANTS FOR LEFT-TURN LANE The benefit-cost methodology presented above was applied to a range of major-road ADTs (1000 to 15,000) and minor-road ADTs (200 to 3000) along with a range of posted speed limits (30 to 60 mph). A service life of 20 years and a minimum rate of return of 4 percent were assumed. The minimum major-road ADT for a given left-turn lane volume that gave a B/C of 1.0 and 2.0 was identified. Initially, the minimum major-road ADT was determined for each posted speed limit; however, minimal differences were identified, primarily because crash costs dominated the calculations and crash prediction is not a function of posted speed limit. Crash predictions are different for rural and urban conditions; therefore, the results will be presented uniquely for rural and urban conditions. Crash predictions also vary by the number of legs at the intersection; therefore, results will also be presented for three-leg and four-leg intersections. The FHWA memo on the economic value of a statistical life recommends that a range be considered in an analysis. Therefore, researchers used the following values (and abbreviations in later figures) in the analysis: • Mid-range = $5.8 million (mid crash), • Low range = $3.2 million (low crash), and • High range = $8.4 million (high crash). The cost to install a left-turn lane can vary from a minimal amount such as the cost to restripe a roadway section to a very large value that would occur if right-of-way needs to be purchased in addition to the construction costs. The range of construction costs selected for the analysis and the abbreviations used to describe the costs in later figures are as follows: • $100,000 (min CC for minimum construction costs), • $250,000 (mod CC for moderate construction costs), and • $375,000 (max CC for maximum construction costs). Plots of Preliminary Warrants Plots were developed to illustrate the resulting warrants for a range of assumed statistical life values and construction costs. The plots selected for illustration in this report are shown in: • Figure 29 for rural two-lane highways showing a range of crash costs (based on $3.2, $5.8, and $8.4 million value of a statistical life), • Figure 30 for rural four-lane highways showing a range of crash costs (based on $3.2, $5.8, and $8.4 million value of a statistical life), • Figure 31 for urban and suburban arterials showing a range of crash costs (based on $3.2, $5.8, and $8.4 million value of a statistical life), • Figure 32 for rural two-lane highways showing a range of construction costs ($100,000, $250,000, and $375,000), • Figure 33 for rural four-lane highways showing a range of construction costs ($100,000, $250,000, and $375,000), and • Figure 34 for urban and suburban arterials showing a range of construction costs ($100,000, $250,000, and $375,000).

115 The figures for rural two-lane highways or urban and suburban arterials also include a representation of the current Green Book warrants. Two lanes, three legs Two lanes, four legs Figure 29. Range of left-turn lane warrants based on crash costs (low, mid-, and high range) for rural two-lane highway. 0 10 20 30 40 50 60 70 80 0 100 200 300 400 500 600 Le ft -T ur n V ol um e (v eh /h r) Opposing Volume (veh/hr/ln) Rural, two lanes, three legs Low Crash, Mod CC Mid Crash, Mod CC High Crash, Mod CC Green Book 60 mph Green Book 40 mph 0 10 20 30 40 50 60 70 80 0 100 200 300 400 500 600 Le ft -T ur n V ol um e (v eh /h r) Opposing Volume (veh/hr/ln) Rural, two lanes, four legs Low Crash, Mod CC Mid Crash, Mod CC High Crash, Mod CC Green Book 60 mph Green Book 40 mph

116 Four lanes, three legs Four lanes, four legs Figure 30. Range of left-turn lane warrants based on crash costs (low, mid-, and high range) for rural four-lane highway. 0 10 20 30 40 50 60 70 80 0 100 200 300 400 500 600 Le ft -T ur n V ol um e (v eh /h r) Opposing Volume (veh/hr/ln) Rural, four lanes, three legs Low Crash, Mod CC Mid Crash, Mod CC High Crash, Mod CC 0 10 20 30 40 50 60 70 80 0 100 200 300 400 500 600 Le ft -T ur n V ol um e (v eh /h r) Opposing Volume (veh/hr/ln) Rural, four lanes, four legs Low Crash, Mod CC Mid Crash, Mod CC High Crash, Mod CC

117 Three legs Four legs Figure 31. Range of left-turn lane warrants based on crash costs (low, mid-, and high range) for urban and suburban highways. 0 10 20 30 40 50 60 70 80 0 100 200 300 400 500 600 Le ft -T ur n V ol um e (v eh /h r) Opposing Volume (veh/hr/approach) Urban, three legs Low Crash, Mod CC Mid Crash, Mod CC High Crash, Mod CC Green Book 60 mph Green Book 40 mph 0 10 20 30 40 50 60 70 80 0 100 200 300 400 500 600 Le ft -T ur n V ol um e (v eh /h r) Opposing Volume (veh/hr/approach) Urban, four legs Low Crash, Mod CC Mid Crash, Mod CC High Crash, Mod CC Green Book 60 mph Green Book 40 mph

118 Two lanes, three legs Two lanes, four legs Figure 32. Range of left-turn lane warrants based on construction costs (minimum, moderate, and maximum) for rural two-lane highways. 0 10 20 30 40 50 60 70 80 0 100 200 300 400 500 600 Le ft -T ur n V ol um e (v eh /h r) Opposing Volume (veh/hr/ln) Rural, 2 Lanes, 3 Legs Mid Crash, Min CC Mid Crash, Mod CC Mid Crash, Max CC Green Book 60 mph Green Book 40 mph 0 10 20 30 40 50 60 70 80 0 100 200 300 400 500 600 Le ft -T ur n V ol um e (v eh /h r) Opposing Volume (veh/hr/ln) Rural, 2 Lanes, 4 Legs Mid Crash, Min CC Mid Crash, Mod CC Mid Crash, Max CC Green Book 60 mph Green Book 40 mph

119 Four lanes, three legs Four lanes, four legs Figure 33. Range of left-turn lane warrants based on construction costs (minimum, moderate, and maximum) for rural four-lane highways. 0 10 20 30 40 50 60 70 80 0 100 200 300 400 500 600 Le ft -T ur n V ol um e (v eh /h r) Opposing Volume (veh/hr/ln) Rural, 4 Lanes, 3 Legs Mid Crash, Min CC Mid Crash, Mod CC Mid Crash, Max CC 0 10 20 30 40 50 60 70 80 0 100 200 300 400 500 600 Le ft -T ur n V ol um e (v eh /h r) Opposing Volume (veh/hr/ln) Rural, 4 Lanes, 4 Legs Mid Crash, Min CC Mid Crash, Mod CC Mid Crash, Max CC

120 Three legs Four legs Figure 34. Range of left-turn lane warrants based on construction costs (minimum, moderate, and maximum) for urban and suburban arterials. 0 10 20 30 40 50 60 70 80 0 100 200 300 400 500 600 Le ft -T ur n V ol um e (v eh /h r) Opposing Volume (veh/hr/approach) Urban, 3 Legs Mid Crash, Min CC Mid Crash, Mod CC Mid Crash, Max CC Green Book 60 mph Green Book 40 mph 0 10 20 30 40 50 60 70 80 0 100 200 300 400 500 600 Le ft -T ur n V ol um e (v eh /h r) Opposing Volume (veh/hr/approach) Urban, 4 Legs Mid Crash, Min CC Mid Crash, Mod CC Mid Crash, Max CC Green Book 60 mph Green Book 40 mph

121 The lines shown in the plots represent the minimum volumes for which a left-turn lane would be recommended based on anticipated delay reduction and crash reduction from adding a left-turn lane to an existing site. In each plot, the point corresponding to the peak-hour major-road volume and the peak-hour left-turn volume should be located. If the point is to the right of the curve shown for the number of lanes and number of legs, then provision of a left-turn lane would be economically justified (i.e., its B/C ratio would be greater than 1.0). If the point is to the left of the curve shown for the appropriate number of lanes and legs, then provision of a left-turn lane is not economically justified (i.e., its B/C ratio would be less than 1.0). Observations Regarding Preliminary Warrants Observations from the graphs include: • Comparing the range of warrants resulting from the range of construction costs and the range of crash costs, much less variability in warrants results when the construction costs are variable by the amounts used in this analysis ($100,000 to $375,000) as can be seen in Figure 32, Figure 33, and Figure 34. A greater range is seen when the crash costs are varied (as shown in Figure 29, Figure 30, and Figure 31). • The warrants for two-lane highways are noticeably smaller than the existing Green Book warrants (as shown in Figure 29). • Left-turn lanes are always warranted on four-leg intersections at lower volumes as compared to three-leg intersections. • Left-turn lanes are warranted on rural two-lane highways at very low volumes (shown in Figure 29). As few as five left-turning vehicles crossing 50 veh/hr/ln results in benefits that outweigh costs when using low- or mid-range crash costs. Even with using high- range crash costs, the benefits are greater than the costs when the five left-turning vehicles are crossing as few as 150 veh/hr/ln for four-leg intersections or 200 veh/hr/ln for three-leg intersections. • Three-leg intersections on urban and suburban arterials have the greatest range in warrant values. Using mid-range crash costs, the warrants range from 50 left-turning vehicles and 100 veh/hr/ln on the major road to five left-turning vehicles and 450 veh/hr/ln on the major road. These warrants are less than the current Green Book warrants. If a low crash cost is assumed, some of the resulting warrants are higher than some of the Green Book warrants (see Figure 31). The primary observation from the graphs that compare the ranges in value for statistical life and construction cost is that the variations in assumed crash cost have a greater impact on the resulting warrants than the variations in assumed construction cost. Other Preliminary Warrants Another approach suggested to account for differences in costs is to utilize a benefit-cost ratio that is higher than 1.0. Plots were developed to illustrate the difference between assuming a benefit-cost ratio of 1.0 (see Figure 35) as compared to 2.0 (see Figure 36) using mid-range crash cost and moderate construction cost. Table 73 provides the warrants in a tabular form. It shows the major-road peak-hour volume that would warrant a left-turn lane for a given left-turn volume using a benefit-cost ratio of 1.0 and 2.0.

122 Suggested left-turn warrants for urban and suburban arterials Suggested left-turn warrants for rural highways Figure 35. Suggested left-turn warrants based on results from benefit-cost evaluation when using B/C of 1.0 and mid-range crash cost and moderate construction cost. 0 10 20 30 40 50 60 70 80 0 100 200 300 400 500 Le ft -T ur n V ol um e (v eh /h r) Opposing Volume (veh/hr/approach) Urban, 3 l egs Urban, 4 l egs Green Book 60 mph Green Book 40 mph 0 10 20 30 40 50 60 70 80 0 100 200 300 400 500 Le ft -T ur n V ol um e (v eh /h r) Opposing Volume (veh/hr/ln) Rural, 2 lanes, 3 legs Rural, 2 lanes, 4 legs Rural, 4 lanes, 3 legs Rural, 4 lanes, 4 legs Green Book 60 mph Green Book 40 mph

123 Suggested left-turn warrants for urban and suburban arterials Suggested left-turn warrants for rural highways Figure 36. Suggested left-turn warrants based on results from benefit-cost evaluation when using B/C of 2.0 and mid-range crash cost and moderate construction cost. 0 10 20 30 40 50 60 70 80 0 100 200 300 400 500 600 700 800 Le ft -T ur n V ol um e (v eh /h r) Opposing Volume (veh/hr/approach) Urban, 3 l egs Urban, 4 l egs Green Book 60 mph Green Book 40 mph 0 10 20 30 40 50 60 70 80 0 100 200 300 400 500 600 700 800 Le ft -T ur n V ol um e (v eh /h r) Opposing Volume (veh/hr/ln) Rural, 2 lanes, 3 legs Rural, 2 lanes, 4 legs Rural, 4 lanes, 3 legs Rural, 4 lanes, 4 legs Green Book 60 mph Green Book 40 mph

124 Table 73. Range of left-turn lane warrants based on results from benefit-cost evaluations using crash costs developed based on FHWA economic value of a statistical life. B/C Ratio Peak-Hour Left-Turn Lane Volume (veh/hr) Peak-Hour Major-Road Volume (veh/hr/ln) Based on Crash Costs Developed Using FHWA Economic Value of a Statistical Life Two Lanes Four Lanes Three legs Four legs Three legs Four legs Rural Urban Rural Urban Rural Urban Rural Urban 1.0 5 50 450 50 50 75 225 50 25 10 50 300 <50 50 75 150 25 25 15 <50 250 <50 50 50 125 25 25 20 <50 200 <50 50 50 100 25 25 25 <50 200 <50 50 50 100 <25 25 30 <50 150 <50 50 50 75 <25 25 35 <50 150 <50 50 50 75 <25 25 40 <50 150 <50 50 50 75 <25 25 45 <50 150 <50 <50 50 75 <25 <25 50 or more <50 100 <50 <50 50 50 <25 <25 2.0 5 200 700 150 250 150 375 125 125 10 100 600 50 200 125 350 75 100 15 100 550 50 150 100 275 50 75 20 50 500 <50 150 100 250 50 75 25 50 450 <50 150 100 225 50 75 30 50 400 <50 100 100 200 25 50 35 50 400 <50 100 100 200 25 50 40 50 350 <50 100 100 175 25 50 45 50 350 <50 100 75 175 25 50 50 50 300 <50 100 75 150 25 50 55 50 300 <50 100 75 150 25 50 60 <50 300 <50 100 75 150 25 50 65 <50 300 <50 100 75 150 25 50 70 or more <50 250 <50 100 75 125 25 50 A greater difference in warrants can be seen for the urban and suburban arterial condition as compared to the rural condition. Even with a benefit-cost ratio of 2.0, the resulting warrants are less than the current Green Book warrants for rural highways (see Figure 36). For four-leg intersections on urban and suburban arterials, a turning volume of 30 veh/hr or more would warrant a left-turn lane when the major-road traffic is 100 veh/hr/approach. The higher benefit- cost ratio did not change that warrant. For lower left-turning volumes, the higher benefit-cost assumption did result in needing a higher peak-hour major-road volume before warranting a left- turn lane. Much higher volumes would need to be met to warrant a left-turn lane on an urban and suburban three-leg intersection (as can be seen when comparing Figure 35 to Figure 36).

125 Since the Highway Safety Manual equations are used, some may argue that the Highway Safety Manual costs should also be used. The warrants resulting from assuming the Highway Safety Manual crash costs (adjusted to 2009 dollars) are listed in Table 74 and illustrated in Figure 37. The resulting warrants are lower when using the Highway Safety Manual costs as compared to using a B/C ratio of 2.0 with the mid-range crash costs and moderate construction costs (see Figure 36). The Highway Safety Manual prediction equations and crash costs provide sensitivity to the number of crashes in the rural versus urban conditions. The crash costs, however, do not provide sensitivity to the number of injuries and deaths for a crash in an urban area as compared to a rural area. Future research should determine how the number of vehicles involved in a crash varies between the rural and urban areas when using a larger dataset than what is available in this study. Table 74. Range of left-turn lane warrants based on results from benefit-cost evaluations using crash costs developed from Highway Safety Manual crash costs. B/C Ratio Peak-Hour Left-Turn Lane Volume (veh/hr) Peak-Hour Major-Road Volume (veh/hr/ln) Based on Highway Safety Manual Crash Costs Two Lanes Four Lanes Three Legs Four Legs Three Legs Four Legs Rural Urban Rural Urban Rural Urban Rural Urban 1.0 5 150 550 100 150 125 350 75 75 10 100 500 50 100 100 250 50 50 15 50 400 <50 100 100 200 25 50 20 50 350 <50 100 75 175 25 50 25 50 300 <50 100 75 150 25 50 30 50 300 <50 50 75 150 25 25 35 50 250 <50 50 75 125 25 25 40 <50 250 <50 50 75 125 25 25 45 <50 250 <50 50 75 125 25 25 50 <50 200 <50 50 75 100 25 25 55 <50 200 <50 50 75 100 <25 25 60 <50 200 <50 50 75 100 <25 25 65 <50 200 <50 50 75 100 <25 25 70 <50 200 <50 50 75 100 <25 25 75 <50 150 <50 50 75 75 <25 25

126 Suggested left-turn warrants for urban and suburban arterials Suggested left-turn warrants for rural highways Figure 37. Suggested left-turn warrants based on results from benefit-cost evaluation when using B/C of 1.0 and HSM crash costs (2009 dollars). IMPACTS DUE TO A NEW DEVELOPMENT There is an inherent difference between adding a left-turn lane at an existing site and constructing a new left-turn lane at a proposed development. This difference was reflected in the explanation of the computation of delay for an existing site and for a new development. At an existing site, the fundamental question is whether a left-turn lane should be provided to alleviate operational and/or safety issues that may be related to the absence of a left-turn lane. In 0 10 20 30 40 50 60 70 80 0 100 200 300 400 500 600 Le ft -T ur n V ol um e (v eh /h r) Opposing Volume (veh/hr/approach) Urban, 3 l egs Urban, 4 l egs Green Book 60 mph Green Book 40 mph 0 10 20 30 40 50 60 70 80 0 100 200 300 400 500 600 700 800 Le ft -T ur n V ol um e (v eh /h r) Opposing Volume (veh/hr/ln) Rural, 2 lanes, 3 legs Rural, 2 lanes, 4 legs Rural, 4 lanes, 3 legs Rural, 4 lanes, 4 legs Green Book 60 mph Green Book 40 mph

127 other words, what is the tradeoff between the benefits that may be achieved and the costs of providing a left-turn lane? For the installation of a left-turn lane at a new development, there are additional questions to answer. As part of its responsibility to manage a roadway network, a transportation agency must decide how/where to spend its limited resources to achieve the maximum benefit to the public. As a result, a process is needed to establish a ranking for which locations should receive priority for having left-turn accommodations provided. The benefit-cost approach enables an agency to make decisions based on estimates of the benefits—in terms of delays and crashes—and costs. Due to limited resources, an agency may often be forced to accept operations and safety conditions that it would have wanted to prevent from occurring. Access management—in particular, the driveway permitting process—is one approach for being proactive. For access to a new development, state and local agencies typically use access permitting to apply access management standards to guide decisions regarding where and what access would be allowed as well as any restrictions to this access. The increasing demands for highway access make it increasingly clear that driveways, and the developments they serve, can have cumulative adverse impacts on the safety and efficiency of the roadway system. While private property enjoys the right of access to the general system of public roadways, this is not an unlimited right. The right of access must be balanced with the needs of and potential harm to the general traveling public. In order to preserve mobility and provide safety for the traveling public, many transportation agencies have established regulations and programs to manage access to their roadway network. The regulations are more restrictive for major arterials, the roadways intended to accommodate higher volumes and speeds. Access management programs restrict the number of driveways allowed as well as the movements allowed that are to be accommodated at the driveways. These practices affect when and where direct driveway access will be allowed onto the roadway network, whether alternative access should be provided, and the need for shared access. If direct access is allowed, the guidance includes the extent of that access (i.e., right in and right out versus full movement) and circumstances in which multiple driveways are allowed. In addition, agencies may require that steps be taken by a developer to mitigate projected traffic operations and/or safety impacts. An example of mitigation is providing a left-turn lane to remove vehicles turning left into the site from the through traffic lanes on an arterial. Many transportation agencies have the authority to require a developer to pay for this mitigation as long as there is a rational nexus between the projected impacts of the development and the needed improvements. In this manner, taxpayers do not have to pay for an improvement that may benefit predominantly one property owner. Transportation agencies that do not have this authority may need to coordinate with the land use authorities to require that needed mitigation be provided at the developer’s expense. Therefore, for a new development the first question for a transportation agency is whether access should be allowed at a particular location or would be preferable at an alternate location. The second question is, if access is allowed, what movements should be permitted. A follow-up

128 question is, if the left-turn inbound movement is allowed, should a left-turn lane be provided, and who should pay for its construction. Example of New Development Additional Annual Delay The findings from this study can also be used to estimate the additional costs to a site if a new development causes left-turn volumes to increase. This example is for the conditions assumed, such as no cross minor-road volumes for a four-leg intersection. Simulation for a specific site would be needed to determine the expected increase in delay for the given intersection characteristics. Assume that the conditions at the site include the following: • Two lanes, • Rural location, • Four legs, • 60-mph posted speed limit, • 488 veh/hr/ln in the peak hour (10,000 ADT on the major road), • 25 veh/hr turning left in the peak hour, • 1000 ADT on the minor road, and • Left-turn lane added on one approach. The amount of additional expected delay during the peak hour is 0.127 sec/veh. This value was determined using the regression coefficients; however, it could also be determined from Figure 24. The delay represents the per-vehicle delay. To determine the delay for all the vehicles at the intersection for that hour, the delay value needs to be multiplied by the number of vehicles at the intersection for that hour, in this example 1001 vehicles (488 through and right-turning vehicles per lane on each approach along with 25 left-turning vehicles). Therefore 66,063 sec of delay occurred during the AM peak hour. With 522 hours in that traffic period, the amount of delay for the year is 18.35 hours. The amount of delay per traffic period is shown in Table 75. For this site, the annual delay cost is $879 assuming a per-hour vehicle cost of $20.01.

129 Table 75. Calculation of annual delay for new development example. Traffic Period Hourly Percent Hours/ Year VTR (veh/ hr) VLT (veh/ hr) DR (sec/ veh) DR (sec) in the Hour DR (sec/Year) DR (hr/Year) AM Peak 10 522 488 25 0.127 127 66,063 18.35 PM Peak 10 522 488 25 0.127 127 66,063 18.35 Off Peak/ Weekend Peak 6.1 2243 297 15 0.010 6 13,682 3.80 Evening 2.8 2555 137 7 0.010 3 7,154 1.99 Night 1.8 2920 88 5 0.010 2 5,256 1.46 158,218 43.95 Dollars per Vehicle Hour Cost $20.01 Annual Delay $879.43 Annual Crash Costs The determination of the costs attributed to crashes begins with calculating the predicted number of crashes for the location. To determine the total number of crash for a roadway, the predicted number of crashes along the segment is added to the predicted number of crashes at the intersection(s). Since the interest within this exercise is to identify the additional crashes associated with this location when it becomes an intersection (now that it has left-turn volume demand due to the new development), using the HSM prediction equation for the intersection is appropriate. The assumption is that the predicted number of segment crashes at this location does not change in the two periods. What changes is the additional crashes estimated due to the location now having intersection-type traffic. The equation for a rural two-lane three-leg intersection is: Nspf 2 ln, 3st = exp[−8.56 + 0.60 × ln(AADTmaj) + 0.61 × ln(AADTmin)] (70) Nspf 2 ln, 3st = exp[−8.56 + 0.60 × ln(10,000) + 0.61 × ln(1000)] Nspf 2 ln, 3st = 3.25 crashes/year The costs per crash at rural four-leg intersections are: • $198,000 (average), • $109,000 (low range), and • $287,000 (high range). Multiplying the cost per crash by the number of crashes that are predicted to occur since the segment now includes an intersection results in the following annual crash costs: • $644,324 (average), • $354,704 (low range), and • $933,945 (high range).

130 Present Worth of Annual Costs The delay and crash costs above represent the expected value per year. Assuming a 20-year design life and a 4 percent return, those annual costs can be converted to a present worth as follows: ܲݎ݁ݏ݁݊ݐ ܹ݋ݎݐ݄ ݋݂ ܥ݋ݏݐݏ ൌ 13.59 ൈ ሺ$879 ൅ $644,324ሻ ൌ $8,768,522 (71)