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

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5 CHAPTER 2 LITERATURE REVIEW—INSTALLATION GUIDELINES A review of the literature was performed using many sources including research reports, state and federal design manuals, and handbooks. Although many procedures are currently in use by various organizations to determine the need for left-turn lanes, several are either very similar or identical. Details are provided below on those methods that appeared to have unique results. LEFT-TURN LANE INSTALLATION GUIDELINES Guidelines Based on Risk Common terms are used in several of the techniques. Figure 1 graphically shows the following movements that are used to determine the need for a left-turn lane in several of the guidelines: • Advancing volume (VA)—the total peak hourly volume of traffic on the major road approaching the intersection from the same direction as the left-turn movement under consideration. • Left-turn volume (VL)—the portion of the advancing volume that turns left at the intersection. • Percent left turns (PL)—the percentage of the advancing volume that turns left; equal to the left-turn volume divided by the advancing volume (PL = [VL ÷ VA] × 100). • Straight-through volume (VS)—the portion of the advancing volume that travels straight through the intersection (VL + VS = VA). • Opposing volume (VO)—the total peak hourly volume of vehicles opposing the advancing volume. Figure 1. Volumes for use in left-turn lane warrant methods. Harmelink Method The oldest research found on evaluating the need for left-turn lanes at unsignalized intersections was that of M. Harmelink (1) in a paper that was published in 1967. His research provided the foundation for many current left-turn guidelines. Harmelink based Advancing Volume (VA) Left-Turning Volume (VL) Straight-Through Volume (VS) Opposing Volume (VO)

6 his work on a queuing model in which arrival and service rates are assumed to follow negative exponential distributions. He states that the probability of a through vehicle arriving behind a stopped, left-turning vehicle should not exceed 0.02 for 40 mph, 0.015 for 50 mph, and 0.01 for 60 mph. He presents his criteria in the form of graphs, 18 in all. To use his graphs, the advancing volume, opposing volume, operating speed, and left- turn percentage need to be known. Graphs for speeds of 40, 50, and 60 mph are given, as well as 5, 10, 15, 20, 30, and 40 percent left-turn volumes. An example graph of Harmelink’s criteria for determining the need for left-turn lanes is shown in Figure 2. Source: Harmelink, M., “Volume Warrants for Left-Turn Storage Lanes at Unsignalized Grade Intersections,” in Highway Research Record 211, Figure 2, p. 9. Copyright, National Academy of Sciences, Washington, D.C., 1967. Reproduced with permission of the Transportation Research Board. Figure 2. Harmelink (1) left-turn lane warrant graph for 40 mph and 5 percent left turns, 1967. AASHTO AASHTO’s A Policy on Geometric Design of Highways and Streets (commonly known as the Green Book) (5) contains a table for use in determining the need for a left-turn lane on two-lane highways (see Table 2). Similar tables are also present in the 2001 (6), 1994 (7), 1990 (8), and 1984 (9) editions of the Green Book. The values in the tables are based upon Harmelink’s work.

7 Table 2. AASHTO (5) guide for left-turn lanes on two-lane highways, 2004. Operating Speed (mph) Opposing Volume (veh/hr) Advancing Volume (veh/hr) 5% Left Turns 10% Left Turns 20% Left Turns 30% Left Turns 40 800 600 400 200 100 330 410 510 640 720 240 305 380 470 515 180 225 275 350 390 160 200 245 305 340 50 800 600 400 200 100 280 350 430 550 615 210 260 320 400 445 165 195 240 300 335 135 170 210 270 295 60 800 600 400 200 100 230 290 365 450 505 170 210 270 330 370 125 160 200 250 275 115 140 175 215 240 NCHRP Report 279 In 1985, the Transportation Research Board published NCHRP Report 279, Intersection Channelization Design Guide (10). In that report, data from Harmelink’s work are used to establish guidelines for determining the need for a left-turn lane. The following advice is provided for unsignalized intersections within new construction: 1. Left-turn lanes should be considered at all median crossovers on divided, high-speed highways. 2. Left-turn lanes should be provided at all unstopped (i.e., through) approaches of primary, high-speed rural highway intersections with other arterials or collectors. 3. Left-turn lanes are recommended at approaches to intersections for which the combination of through, left, and opposing volumes exceeds the warrants shown in Figure 3. 4. Left-turn lanes on stopped or secondary approaches should be provided based on analysis of the capacity and operations of the unsignalized intersection. Considerations include minimizing delays to right-turning or through vehicles and total approach capacity.

8 Source: Neuman, T., Intersection Channelization Design Guide, NCHRP Report 279. Copyright, National Academy of Sciences, Washington, D.C., 1985. Figure 3. NCHRP Report 279 (10) left-turn lane guidelines, 1985. NCHRP Report 279 also provides guidance for reconstruction/rehabilitation. The report states: Addition of left-turn lanes at existing intersections should be considered if safety or capacity problems occur, or if land-use changes are expected to produce significant shifts in local traffic patterns (such as increases in left-turn demand). Left-turn lanes can often be added within existing street widths by removing parking, narrowing of lanes or a combination of the two. The traffic volume guidelines described for new intersections are also appropriate for evaluating the need for left-turn lanes at existing intersections. In terms of safety, the following guidelines are suggested: • Left-turn lanes should be considered at intersection approaches that experience a significant number of left-turn-involved (rear-end, left-turn angle, or same direction sideswipe) accidents. A total of four or more such accidents in 12 months, or six or more in 24 months, is considered appropriate.

9 • When room for separate left-turn lanes is not available, traffic control alternatives should be investigated. Such alternatives to left-turn lane implementation include split phasing at signalized intersections (i.e., operating each approach individually) or prohibition of left turns. Oppenlander and Bianchi (ITE Technical Committee) Institute of Transportation Engineers (ITE) Technical Committee 4A-22 (11) in the 1980s undertook the task of developing criteria for the provision of separate left-turn lanes at unsignalized and signalized intersections. The work performed by ITE Committee 4A-22 expanded the Harmelink model to include additional speeds (30- and 70-mph roadways) and to include additional left-turn percentages. An example of one of the guideline graphs produced is shown in Figure 4. Source: Copyright, Institute of Transportation Engineers, Washington, D.C., www.ite.org, 1990. Reproduced with permission. Figure 4. Oppenlander and Bianchi (11) left-turn lane guidelines; unsignalized, two-lane, 30-mph operating speed, 1990.

10 NCHRP Report 457 In 2001, Bonneson and Fontaine (12) in NCHRP Report 457 discussed the determination of when to consider a left-turn lane. They cited work by Neuman (10) (which was based on the Harmelink model) and re-created the Harmelink model as an interactive spreadsheet (available on the Internet in the NCHRP report at http://trb.org/publications/nchrp/esg/esg.pdf). Fitzpatrick and Wolff In 2003, Fitzpatrick and Wolff (13) used the following findings from current research in the Harmelink model: • Critical gap of 5.5 sec (rather than 5.0 sec), • Time to make a left turn of 4.3 sec (rather than 3.0 sec), and • Time to clear the lane of 3.2 sec (rather than 1.9 sec). Table 3 lists the developed suggested guidelines for installing left-turn lanes for operating speeds of 30, 50, and 70 mph. Figure 5 illustrates the changes in the curves for 30 and 70 mph between Fitzpatrick and Wolff and AASHTO. Source: Fitzpatrick, K., and T. Wolff, “Left-Turn Lane Installation Guidelines,” in 2nd Urban Street Symposium, sponsored by Transportation Research Board, July 2003. Reproduced with permission of the authors. Figure 5. Fitzpatrick and Wolff (13) comparison of existing to proposed guidelines (example uses 10 percent left turns), 2003. 0 200 400 600 800 0 100 200 300 400 500 600 700 Advancing Volume (Va), veh/h O pp os in g Vo lu m e (V o) , ve h/ h 30 mph proposed 30 mph existing 70 mph proposed 70 mph existing

11 Table 3. Fitzpatrick and Wolff (13) guidelines for installing left-turn lanes on two-lane highways, 2003. Speed (mph) Vo Percent Left Turns 10 20 40 30 800 700 600 500 400 300 200 100 0 197 217 238 261 286 314 345 380 418 148 162 178 196 215 236 259 285 313 121 133 146 160 175 193 211 232 256 50 800 700 600 500 400 300 200 100 0 153 168 184 202 222 244 268 294 323 115 126 138 152 166 183 201 221 243 94 103 113 124 136 149 164 180 198 70 800 700 600 500 400 300 200 100 0 88 97 106 117 128 141 154 170 187 66 73 80 88 96 105 116 127 140 54 59 65 71 78 86 95 104 114 Van Schalkwyk and Stover In 2007, Van Schalkwyk and Stover (14) discussed additional refinements to the Harmelink curves with a focus on the needs of older drivers. Their paper includes a table of recommended left-turn warrants (see Table 4). They concluded that the left-turn warrants based on Harmelink’s 1967 work substantially overestimate the volumes that warrant left-turn lanes. In addition to older driver consideration, they recommended additional research into the differences between positioned and unpositioned drivers.

12 Table 4. Van Schalkwyk and Stover (14) recommended left-turn warrants on two-lane highways to accommodate the needs of older drivers, 2007. Speed (mph) Vo Percent Left Turns 10 20 40 40 100 200 300 400 500 600 700 800 214 189 167 147 129 113 99 87 160 142 125 110 97 85 74 65 131 116 102 90 79 69 61 53 50 100 200 300 400 500 600 700 800 185 164 144 127 112 98 86 75 139 123 108 95 84 74 64 56 113 100 88 78 69 60 53 46 60 100 200 300 400 500 600 700 800 151 134 118 104 91 80 70 61 113 100 88 78 69 60 53 46 93 82 72 64 56 49 43 38 Guidelines Based on Approaching Volumes NCHRP Report 348 F.J. Koepke and H.S. Levinson provide two methods for determining the need for left-turn lanes in NCHRP Report 348 (15). The first method is shown in Figure 6; however, Koepke and Levinson state that in most cases, left-turn lanes should be provided where there are more than 12 left turns per peak hour. The second method presents the values included in the Green Book for determining whether a left-turn lane should be provided. They also state that “left-turn lanes should be provided when delay caused by left-turning vehicles blocking through vehicles would become a problem.” They emphasize the fact that separate left-turn lanes not only increase intersection capacity but also increase vehicle safety.

13 (a) 30–35 mph (b) 40–45 mph Source: Koepke, F.J., and H.S. Levinson, Access Management Guidelines for Activity Centers, NCHRP Report 348. Copyright, National Academy of Sciences, Washington, D.C., 1992. Figure 6. NCHRP Report 348 (15) left-turn lane guidelines, 1992. Guidelines Developed Using Simulation Models Modur et al. A 1990s Texas study by Modur et al. (16) examined the choice of median design and developed a set of guidelines for determining when to recommend left-turn lanes for arterial streets with speeds less than 45 mph. The guidelines were developed using delay data generated from a simulation model. Table 5 shows the developed guidelines. The authors note that sections with left-turn treatments are better than sections with no treatments, and they recommend that left-turn treatments be used in sections with a disproportionately large number of crashes even though not warranted due to the operational criteria. Hawley and Stover Hawley and Stover (17) also used delay to generate guidelines on when to install a left-turn lane on four-lane undivided arterials. They considered the delay to through vehicles and asked under what volumes turning vehicles would seriously impact through traffic. They then evaluated the proposed guidelines with a conflict analysis that was based on the probability of two vehicles arriving at the intersection at the same time to assess the safety aspects of the guidelines. A probability of 0.01 was selected as the maximum likelihood of a conflict. The philosophy of the new guidelines focuses on recommending a left-turn lane above a set directional volume rather than a set turn volume. Figure 7 is a graph of the curves recommended. It was developed with consideration of delay (the curved portion of the curves in Figure 7) and probability of a conflict between a left-turning vehicle and advancing vehicles (the horizontal portions of the curves in Figure 7).

14 Table 5. Modur et al. (16) left-turn lane warrant chart, 1990. Opposing Traffic Volume per Lane per Hour 400–600 < 200 Hourly Left-Turn Traffic Volume 200–400 0–200 400–600 200–400 200–400 0–200 400–600 400–600 200–400 0–200 0–150 150–300 300–450 Hourly Straight Through Traffic Volume per Lane Black boxes denote that a left-turn treatment is desirable, provided it can be accommodated within the available right-of-way and pavement width. Gray boxes mean that an operational left-turn treatment may be considered; a left-turn lane or raised median is satisfactory based on individual site considerations. White boxes signify that no left-turn treatment is required based on operational considerations. Source: Hawley, P., and V. Stover, “Guidelines for Left-Turn Bays at Unsignalized Access Locations,” in Second National Access Management Conference: Conference Proceedings, Figure 3, p. 388. Copyright, National Academy of Sciences, Washington, D.C., 1996. Reproduced with permission of the Transportation Research Board. Figure 7. Hawley and Stover (17) left-turn lane guidelines for four-lane undivided arterial street with nonplatoon flow, 1996. Lakkundi et al. Ranade et al. (18) reported on a 2004 study by Lakkundi et al. that developed a set of warrants on the basis of event-based simulation programs that the authors developed and calibrated using six intersections in Virginia. The simulation allowed for stochastic variations in drivers’ gap

15 acceptance behavior. Ranade et al. commented that the warrants developed were based on the probability criterion suggested by Harmelink. Guidelines Based on a Combination of Approaches Kikuchi and Chakroborty A 1991 paper (19) discusses three approaches to justifying a left-turn lane: 1. Modification to Harmelink’s methodology, 2. Delay (average delay to the “caught” through vehicles, average delay to all through vehicles, and delay savings due to the left-turn lane), and 3. Degradation of level of service. The delay values were determined using simulation. Figure 8 shows an example of the criteria for 10 percent left turns using the three approaches. Other assumptions used in developing the figure include: • The probability used in Harmelink’s methodology is 0.02. • The average delay to the through vehicles caught in the queue was assumed to be 19 sec. • The level of service (LOS) changes from A to B at a through movement capacity of 1800 veh/hr. The authors support the guidelines developed based on delay or based on level of service because delay and level of service are easier to understand than probability. They note that the precise limits should vary based on the standards of the community and other factors such as the accident experience and the number of buses included in the through vehicles. Ranade et al. A 2007 paper (18) presents the concept of using an estimate of the benefits of left-turn lane installations at unsignalized intersections as the method to determine when to warrant a left-turn lane. The authors developed a refined decision support system (DSS) for assessing the likely benefits of left-turn lane installations as an aid to deciding whether a left-turn lane is warranted. The developed DSS was designed to predict likely benefits based on: • Delay savings, • Reductions in percent stops, • Increases in fuel efficiency, and/or • Reductions in emissions.

16 Source: Kikuchi, S., and P. Chakroborty, “Analysis of Left-Turn-Lane Warrants at Unsignalized T-Intersections on Two-Lane Roadways,” in Transportation Research Record 1327, Figure 7, p. 88. Copyright, National Academy of Sciences, Washington, D.C., 1991. Reproduced with permission of the Transportation Research Board. Figure 8. Kikuchi and Chakroborty (19) left-turn lane guidelines using three methods, 1991. The first step in developing the DSS was to use microscopic simulation to model several real- world unsignalized intersections with different geometric configurations and located in different area types. After calibrating these models, several scenarios covering a wide range of operational conditions were simulated. The output from these simulation runs was then used to train a set of multilayer perceptron neural networks (NNs). The NNs can then be incorporated into a DSS that can be used to quantify the impacts of a proposed new development as well as estimate the benefits of left-turn lane installations. The authors used the NNs to develop warrants for left-turn lane installations similar to those proposed by Harmelink. Their illustration used a two-lane urban road with an operating speed of 40 mph and 30 percent left turns. They based their case study warrants on the criterion of the total number of stops in the advancing stream. Compared to the original and modified Harmelink models (Kikuchi and Chakroborty), the newly developed warrants allow higher volume combinations before recommending a left-turn lane (see Figure 9). 0 200 400 600 800 0 500 1000 1500 2000 O pp os in g Vo lu m e (v ph ) Advancing Volume (vph) Delay Based Modified Harmelink LOS(A-B)

17 Source: Ranade, S., A. Sadek, and J. Ivan, “Decision Support System for Predicting Benefits of Left-Turn Lanes at Unsignalized Intersections,” in Transportation Research Record 2023, Figure 7, p. 36. Copyright, National Academy of Sciences, Washington, D.C., 2007. Reproduced with permission of the Transportation Research Board. Figure 9. Ranade et al. (18) and previous studies (1, 19) comparison of left-turn lane warrants (assuming 40-mph speed and 30 percent left turns), 2007. Summary of Guidelines from Literature A summary of the findings from the literature can be placed into two major groups—those based on the Harmelink procedure and those based on other procedures. Table 6 summarizes guidelines on warranting a left-turn lane based on the Harmelink procedure. Table 7 summarizes other procedures for warranting left-turn lanes. Guidelines in State Manuals Several state manuals also include information on when to consider a left-turn lane. Table 8 summarizes the findings. 0 200 400 600 800 0 200 400 600 800 Opposing Volume (veh/hr) A dv an ci ng V ol um e (v eh /h r) Harmelink Kikuchi & Chakroborty Ranade et al. Lakkundi et al.

18 Table 6. Summary of selected left-turn lane literature guidelines based on Harmelink procedure. Method AASHTO (5, 7, 8, 9) NCHRP Report 279 (10), NCHRP Report 457 (12) Oppenlander and Bianchi (11) Fitzpatrick and Wolff (13) Van Schalkwyk and Stover (14) Year(s) 2001, 1994, 1990, 1984 1985, 2001 1990 2003 2007 Roadway Type Two-lane Two-way stop controlled Two-lane unsignalized Two-lane unsignalized Two-lane unsignalized Developed with Consideration of: Minimize conflict Minimize conflict Minimize conflict and increase safety Minimize conflict Minimize conflict Key Feature Based on Harmelink’s 1967 study; developed table of values for various speeds and left-turn percentages Based on Harmelink’s 1967 study; NCHRP Report 457 includes a spreadsheet to perform calculations Used Harmelink’s model and expanded to additional speed ranges; also added consideration of crashes Updated variables used in Harmelink’s model Updated variables used in Harmelink’s model Crashes “…safety considerations are sufficient to warrant them.” States that there are benefits in crash reduction when left- turn lane is added Crashes by approach that would involve a left-turning vehicle: 4 per year at unsignalized and 5 per year at signalized Not considered Not considered Table 7. Summary of selected left-turn lane literature guidelines based on approaching volume, delay, or combination of approaches. Method NCHRP Report 348 (15) Modur et al. (16) Hawley and Stover (17) Kikuchi and Chakroborty (19) Ranade et al. (18) Year(s) 1992 1990 1996 1991 2007 Roadway Type Any unsignalized Urban (roadways less than 45 mph) Four-lane undivided Two-lane unsignalized Two-lane unsignalized Developed with Consideration of: Not specified Delay Delay 3 approaches: • Modify Harmelink • Delay • Degradation of LOS Benefits based on: • Delay • Reduction in percentage of stops • Increase in fuel efficiency • Reduction in emissions Key Feature Would recommend lower left-turn volumes than other methods Used simulation to determine guidelines Used results from simulation to determine value Consider delay or level of service easier to understand than probability Simulation used to train a set of multilayer perception neural networks Crashes “Separate turning lane …promote the safety of all traffic.” “Sections with left-turn treatments are always better than the sections with no treatment.” Guidelines checked against maximum probability of conflict of 0.01; recommends consideration of potential crashes Accident experience should be considered Not considered

19 Table 8. Summary of state methods. Primary Procedure Consideration of: State G re en B oo k 27 9 G ra ph s 27 9 G ui da nc e G en er al G ui da nc e U ni qu e G ui da nc e M ed ia n O pe ni ng s Sp ec ifi c O ffi ce 1 C ra sh es /S af et y C la ss ifi ca tio n C on si st en cy Si gh t D is ta nc e C ap ac ity E va l. C os t C at al ys t2 La nd U se Alaska    Arizona  California  Colorado     Connecticut        Delaware        Florida   Georgia     Illinois        Indiana          Iowa   Kentucky    Louisiana       Massachusetts     Minnesota           Mississippi       Missouri   Montana       Nebraska     Nevada   New Jersey   New Mexico  New York      Ohio    Oregon     Pennsylvania  South Dakota     Tennessee   Texas   Utah    Virginia    Washington     1 Decision is made within a specific office within the department of transportation. 2 Criteria may vary by catalyst that triggers consideration of left-turn accommodation: major reconstruction (or new construction), spot improvement, or development.

20 Based on Green Book The following nine state manuals either include the same table of criteria as the values included in the Green Book (5) for determining the need for a left-turn lane or reference the Green Book: • Alaska Highway Preconstruction Manual (20), • Delaware’s DelDOT Road Design Manual (21), • Indiana Design Manual (22), • Nevada Access Management System and Standards (23), • The Commonwealth of Massachusetts Highway Design Guidebook (24), • New York Highway Design Manual (25), • Texas Roadway Design Manual (26), • Virginia Road Design Manual (27), and • Washington Design Manual (28). Three of these states also included information from NCHRP Report 279 (10) or from Harmelink’s original paper (1). These nine states also typically provided general guidelines regarding left-turn lanes. For example, the Indiana Design Manual (22) states: The accommodation of left turns is often the critical factor in proper intersection and median-opening design. A left-turn lane can significantly improve both the level of service and intersection safety. An exclusive left-turn lane should be provided as follows: • At each intersection on an arterial, where practical; • At each intersection on a divided urban or rural highway with a median wide enough to accommodate a left-turn lane, provided that adequate spacing exists between intersections; • At an unsignalized intersection on a two-lane urban or rural highway which satisfies the criteria shown in [a table that contains the Green Book values]; • At an intersection where a capacity analysis determines that a left-turn lane is necessary to meet the level-of-service criteria, including multiple left-turn lanes; • At a signalized intersection where the design-hour left-turning volume is 60 veh/h or more for a single turn lane, or where capacity analysis determines the need for a left-turn lane; • For uniformity of intersection design along the highway if other intersections have left-turn lanes in order to satisfy driver expectancy; • At an intersection where the accident experience, traffic operations, sight distance restrictions (e.g., intersection beyond a crest vertical curve), or engineering judgment indicates a significant conflict related to left-turning vehicles; or • At a median opening where there is a high volume of left turns, or where vehicular speeds are 50 mph or higher.

21 Delaware’s DelDOT Road Design Manual (21) states that for unsignalized intersections, left-turn lanes should be provided: • At all median openings on high-speed divided highways, • On approaches where sight distance is limited, • At non-stopping approaches of rural arterials and collectors, and • At other approaches where required based on capacity and operational analysis. The manual also notes that there may be other needs, primarily safety, for left-turn lanes at other locations than mentioned in the general guidelines. For two-lane roadways, a high-volume, intersecting minor roadway or entrance may also create the need to separate movements with auxiliary turning lanes. The manual includes tabulated values similar to the values in the Green Book. The Indiana Design Manual (22) provides information on warrants for passing blisters. Passing blisters are used to relieve congestion due to left-turning vehicles. Appendix B includes a copy of a layout for a passing blister. Indiana states the following is to be reviewed to determine the need for a passing blister: • Traffic volume. A passing blister may be provided at the intersection of a public road or street with a two-lane state highway with a design-year AADT [annual average daily traffic] of 5000 or greater. For a two-lane state highway with a design-year of less than 5000, a passing blister should be used only if one or more of the following occurs: o There is an existing passing blister. o There are 20 or more left-turning vehicles during the design hour. o Accident reports or site evidence, such as skid marks in the through lane displaying emergency braking, indicate potential problems with left-turning vehicles. o The shoulder indicates heavy use (e.g., dropped shoulder, severe pavement distress). • The decision on whether to use either a channelized left-turn lane or a passing blister should be based on accident history, right-of-way availability, through- and turning-traffic volumes, design speed, and available sight distance. A channelized left-turn lane should be provided if the left-turning volume is high enough that a left-turn lane is warranted. Based on NCHRP Report 279 The state manuals that include the graphs available in NCHRP Report 279 along with some of the recommendations are: • Connecticut’s ConnDOT Highway Design Manual (29), • Illinois’ Bureau of Design and Environment Manual (30), • Mississippi’s Roadway Design Manual (31), • Missouri Engineering Policy Guide (32), • Montana’s Road Design Manual (33), and • Tennessee’s TDOT Roadway Design Guidelines (34).

22 For example, the Connecticut manual (29) states: In general, exclusive left-turn lanes should be provided for at-grade intersections as follows: 1. on all divided urban and rural highways with a median wide enough to allow a left-turn lane (this applies to intersections with public roads and to major traffic generators); 2. for all approaches at arterial/arterial intersection; 3. at any unsignalized intersection on a two-lane urban or rural highway which satisfies the criteria in Figures 11-5B, 11-5C, 11-5D, 11-5E or 11-5F [These figures are based on NCHRP Report 279, which is based on Harmelink. The figures also include graphs for 55 and 45 mph, which were not included in NCHRP Report 279. The Connecticut manual does not include the four-lane undivided graph.]; 4. at any intersection where a capacity analysis determines a left-turn lane is necessary to meet the level-of-service criteria; 5. at any intersection included or expected to be within an interconnected signal system where the presence of standing left-turning vehicles would disrupt the progression of platoon traffic; or 6. at any intersection where the crash experience, traffic operations, sight distance restrictions or engineering judgment indicates a significant problem related to left-turning vehicles. The Missouri (32) and Tennessee (34) manuals also include the NCHRP Report 279 graphs, but with different descriptive text. The Tennessee manual includes a reference to the Green Book. The Nebraska manual (35) refers the reader to the NCHRP report. The following states include most of the recommendations from NCHRP Report 279, without referencing the graphs: • Colorado (36) and • Kentucky (37). For example, the Colorado Design Guide (36) includes the following guidelines to facilitate flow where the intersection is unsignalized: • Left-turn lanes should be considered at all median crossovers on divided, high- speed highways. • Left-turn lanes should be provided at all uncontrolled approaches of primary, high-speed rural highway intersections with other arterials and collectors. • Left-turn lanes should be provided on stopped or secondary approaches based on analysis of the capacity and operations of the unsignalized intersection. Additional material on when to consider deceleration or acceleration lanes is included in Colorado’s State Highway Access Code, Volume 2, Code of Colorado Regulations 601-1 (38). Criteria are provided by road class. Table 9 lists the criteria.

23 Table 9. Colorado Access Code (38) criteria for deceleration lanes. Category of Road Criteria Expressway, Major Bypass A left-turn deceleration lane is required for any access with a projected average daily left- turn ingress volume greater than 10. The transition taper length will be included within the required deceleration length. If the projected peak-hour left-ingress turning volume is greater than 10 veh/hr, a left-turn lane with deceleration, storage, and transition taper lengths is required for any access. Regional Highway A left-turn deceleration lane with taper and storage length is required for any access with a projected peak-hour left-ingress turning volume greater than 10 veh/hr. The taper length will be included within the required deceleration length. Rural Highway A left-turn deceleration lane with taper and additional storage length is required for any access with a projected peak-hour left-ingress turning volume greater than 10 veh/hr. The taper length shall be included within the required deceleration length. Non-rural Principal Highways A left-turn deceleration lane and taper with storage length is required for any access with a projected peak-hour ingress turning volume greater than 10 veh/hr. The taper length will be included within the required deceleration length. Non-rural Arterial A left-turn lane with storage length plus taper length is required for any access with a projected peak-hour left-ingress turning volume greater than 25 veh/hr. If the posted speed is greater than 40 mph, a deceleration lane and taper are required for any access with a projected peak-hour left-ingress turning volume greater than 10 veh/hr. The taper length will be included within the deceleration length. Frontage Road A left-turn lane with storage length plus taper length is required for any access with a projected peak-hour left-ingress turning volume greater than 25 veh/hr. If the posted speed is greater than 40 mph, a deceleration lane and taper are required for any access with a projected peak-hour left-ingress turning volume greater than 10 veh/hr. The taper length will be included within the deceleration length The Ohio Location and Design Manual (39) Section 400 (Intersection Design) states: Probably the single item having the most influence on intersection operation is the treatment of left turn vehicles. Left-turn lanes are generally desirable at most intersections. However, cost and space requirements do not permit their inclusion in all situations. Intersection capacity analysis procedures of the current edition of the Highway Capacity Manual should be used to determine the number and use of left-turn lanes. For unsignalized intersections, left-turn lanes may also be needed if they meet warrants as provided in [figures that appear to be based on Green Book and NCHRP Report 279 information]. The warrants apply only to the free- flow approach of the unsignalized intersection. Based on Harmelink The New Jersey Roadway Design Manual Section 6: At-Grade Intersections (40) includes general guidance comments. The New Jersey Administrative Code (41) references the Harmelink paper directly: A left-turn lane shall be provided for access points on State highway segments with access level 4 when the criteria set forth in…Highway Research Record 211, Volume Warrants for Left-Turn Storage Lanes at Unsignalized Grade Intersections, incorporated herein by reference, are met. Left-turn access shall be prohibited if the criteria have been met but there is insufficient space for a left- turn lane, unless the Commissioner determines that left-turns can be made safely, considering traffic volumes and sight distances.

24 General Guidance General guidance is provided in publications from: • Florida Driveway Information Guide (42), • Louisiana’s Roadway Design Procedures and Details (43), • New Jersey Roadway Design Manual Section 6: At-Grade Intersections (40), and • Pennsylvania’s Design Manual, Part 2 Highway Design (44). For example, Louisiana’s Roadway Design Procedures and Details states: “On new four-lane highways, left-turn lanes are usually provided at all intersecting side roads that have dedicated right-of-way.” The New Jersey Roadway Design Manual Section 6: At-Grade Intersections states: “Median lanes may be provided at intersections and other median openings where there is a high volume of left-turns, or where vehicular speeds are high on the main roadway.” Chapter 1 of Pennsylvania’s Design Manual, Part 2 Highway Design, states: “The warrants for the use of speed-change lanes cannot be stated definitely. However, based on observations and past experience, the following general conclusions have been made: 1. Speed-change lanes are warranted on high-speed and on high-volume highways where a change in speed is necessary for vehicles entering or leaving the through-traffic lanes.” The Florida Driveway Information Guide states that whenever a driveway is directly served by a median opening, a left-turn lane should be available. This provides for the safest left turns into the driveway. For two-lane roadways, exclusive left-turn lanes should be considered at any location serving the public, especially on curves and where speeds are 45 mph and higher. Unique Criteria The following states have unique criteria or procedures for determining when a left-turn lane should be considered: • Georgia (45), • New Mexico (46), • Iowa (47), • Nevada (23), • Minnesota (48, 52), • Oregon (49), • South Dakota (50), and • Utah (51). Utah’s Roadway Design Manual of Instruction (51) states: “Under conditions of relatively high traffic volumes, traffic congestion problems can be significantly alleviated with auxiliary lanes to handle turning movements. In rural areas, consider left-turn lanes where there are 25 or more left-turn movements from the main highway in the peak hour.” Georgia’s Regulations for Driveway and Encroachment Control (45) states: Left-turn lanes must be constructed at no cost to the Department if the daily site generated left-turn volumes (LTV) based on ITE Trip Generation (assuming a reasonable distribution of entry volumes) meet or exceed the values shown in Table [10] Condition 1. If the LTVs are below the requirements for Condition 1,

25 the applicant may be required to construct a Right Hand Passing Lane if they meet the criteria in Table [11] Condition 2. The District Access Management Engineer will use engineering judgment to determine if the field conditions would allow construction of the Right Hand Passing Lane [see Appendix B]. Passing lane sections fall under the criteria for two or more lanes. In the event the District Access Management Engineer determines that field conditions or other factors indicate that it would be in the best interest of the Department to waive the left-turn lane requirement, the District Access Management Engineer must document the recommendations using the form in Appendix E [of the Georgia Manual]. The recommendations shall be approved by the District Engineer and be attached to the Permit. The District Access Management Engineer may also require the addition of a Left-turn lane, even when the conditions in Table [9] are not met, if roadway geometry or field conditions indicate that the safety of the traveling public would be improved. The recommendation must be documented and approved by the District Engineer for inclusion with the Permit. Table 10. Georgia (45) regulations for driveway and encroachment control left-turn requirements, condition 1. Condition 1: Left-Turn Requirements—Full Construction Posted Speed 2 Lane Routes More than 2 Lanes on Main Road < 6000 ADT ≥ 6000 ADT < 10,000 ADT ≥ 10,000 ADT 35 mph or less 40 to 50 mph ≥ 55 mph 300 LTV a day 250 LTV a day 200 LTV a day 200 LTV a day 175 LTV a day 150 LTV a day 400 LTV a day 325 LTV a day 250 LTV a day 300 LTV a day 250 LTV a day 200 LTV a day ADT = average daily traffic LTV = left-turn volume Table 11. Georgia (45) regulations for driveway and encroachment control left-turn requirements, condition 2. Condition 2: Left-Turn Requirements with Right-Hand Passing Lane Option Posted Speed 2 Lane Routes Only < 4000 ADT ≥ 4000 ADT 35 mph or less 40 to 50 mph ≥ 55 mph 200 LTV a day 100 LTV a day 75 LTV a day 125 LTV a day 75 LTV a day 50 LTV a day ADT = average daily traffic LTV = left-turn volume New Mexico’s State Access Management Manual (46) contains details on criteria for left-turn lanes. The information is shown in the following tables: • Table 12 for urban two-lane highways, • Table 13 for urban multilane highways, • Table 14 for rural two-lane highways, and

26 • Table 15 for rural multilane highways. Table 12. New Mexico (46) criteria for deceleration lanes on urban two-lane highways. Table 17.B-1. Criteria for Deceleration Lanes on Urban Two-Lane Highways Turning Volume1 (veh/hr) Left-Turn Deceleration Lane Right-Turn Deceleration Lane Minimum Directional Volume in the Through Lane (veh/hr/ln)2 Minimum Directional Volume in the Through Lane (veh/hr/ln)2 ≤ 30 mph 35–45 mph 45–55 mph ≤ 30 mph 35–40 mph 45–55 mph < 5 Not required Not required Not required Not required Not required Not required 5 510 450 330 1080 610 360 10 390 330 210 700 400 240 15 320 250 150 500 280 170 20 270 200 120 380 210 140 25 230 160 100 300 180 120 30 200 130 Required 250 160 110 35 170 110 Required 220 150 100 40 150 Required Required 200 140 Required 45 130 Required Required 190 Required Required ≥ 46 Required Required Required Required Required Required Left-turn deceleration lanes are required on urban two-lane highways for the following left-turn volumes: • ≤ 30 mph: 46 veh/hr or more • 35 to 40 mph: 36 veh/hr or more • 45 to 55 mph: 26 veh/hr or more Right-turn deceleration lanes are required on urban two-lane highways for the following right-turn volumes: • ≤ 30 mph: 46 veh/hr or more • 35 to 40 mph: 41 veh/hr or more • 45 to 55 mph: 36 veh/hr or more Notes: 1. Use linear interpolation for turning volumes between 5 and 45 veh/hr. 2. The directional volume in the through lane includes through vehicles and turning vehicles.

27 Table 13. New Mexico (46) criteria for deceleration lanes on urban multilane highways. Turning Volume1 (veh/hr) Left-Turn Deceleration Lane Right-Turn Deceleration Lane Minimum Directional Volume in the Adjacent Through Lane (veh/hr/ln)2 Minimum Directional Volume in the Adjacent Through Lane (veh/hr/ln)2 ≤ 30 mph 35–45 mph 45–55 mph ≤ 30 mph 35–40 mph 45–55 mph < 5 Not Required Not Required Not Required Not Required Not Required Not Required 5 Not required 490 420 1200 730 450 10 420 370 300 820 490 320 15 360 290 220 600 350 240 20 310 230 160 460 260 180 25 270 190 130 360 230 150 30 240 160 110 290 200 130 35 210 130 100 260 180 120 40 180 120 Required 240 170 110 45 160 110 Required 220 160 Required ≥ 46 140 Required Required 200 Required Required Left-turn deceleration lanes are required on urban multilane highways for the following left-turn volumes: • ≤ 30 mph: 56 veh/hr or more • 35 to 40 mph: 46 veh/hr or more • 45 to 55 mph: 36 veh/hr or more Right-turn deceleration lanes are required on urban multilane highways for the following right-turn volumes: • ≤ 30 mph: 56 veh/hr or more • 35 to 40 mph: 46 veh/hr or more • 45 to 55 mph: 41 veh/hr or more Notes: 1. Use linear interpolation for turning volumes between 5 and 55 veh/hr. 2. The directional volume in the adjacent through lane includes through vehicles and turning vehicles.

28 Table 14. New Mexico (46) criteria for deceleration lanes on rural two-lane highways. Left-Turn Volume1 (veh/hr) Left-Turn Deceleration Lane Minimum Directional Volume in Through Lane (veh/hr/ln)2 ≤ 30 mph 35–40 mph 45–55 mph > 55 mph < 5 Not required Not required Not required Not required 5 400 200 120 60 10 240 140 80 40 15 160 100 60 Required 20 120 80 Required Required 25 100 Required Required Required ≥ 26 Required Required Required Required Left-turn deceleration lanes are required on rural two-lane highways for the following left-turn volumes: • ≤ 30 mph: 26 veh/hr or more • 35 to 40 mph: 21 veh/hr or more • 45 to 55 mph: 16 veh/hr or more • > 55 mph: 11 veh/hr or more Notes: 1. Use linear interpolation of left-turn volumes between 5 and 25 veh/hr. 2. The directional volume in the through lane includes through vehicles and turning vehicles. Table 15. New Mexico (46) criteria for deceleration lanes on rural multilane highways. Left-Turn Volume1 (veh/hr) Left-Turn Deceleration Lane Minimum Directional Volume in Through Lane (veh/hr/ln)2 ≤ 30 mph 35–40 mph 45–55 mph > 55 mph < 5 Not required Not required Not required Not required 5 400 200 120 60 10 240 140 80 40 15 160 100 60 Required 20 120 80 Required Required 25 100 Required Required Required 30 130 Required Required Required 35 110 Required Required Required ≥ 36 Required Required Required Required Left-turn deceleration lanes are required on rural multilane highways for the following left-turn volumes: • ≤ 30 mph: 36 veh/hr or more • 35 to 40 mph: 26 veh/hr or more • 45 to 55 mph: 21 veh/hr or more • > 55 mph: 16 veh/hr or more Notes: 1. Use linear interpolation of left-turn volumes between 5 and 35 veh/hr. 2. The directional volume in the through lane includes through vehicles and turning vehicles.

29 The Iowa Design Manual material is shown in Table 16. Note the left-turning volume criteria are for a deceleration lane rather than the left-turn bay. Left-turn lanes are to be provided at all Type A entrances (greater than 150 veh/hr) and Type B entrances (moderate traffic volume, 20 to 150 veh/hr). Oregon and South Dakota have similar criteria. Table 17 and Table 18 show South Dakota’s procedure. Both states consider vehicular volume, crash experience, and special cases. Table 16. Iowa (47), left-turn lane material. Left-turn lanes Left-turn lanes provide storage in the median for left-turning vehicles, or when warranted, deceleration outside of the through traffic lanes for left-turning vehicles. All Type “A” and high volume Type “B” entrances should have left-turn lanes provided; see Section 3E-2 of this manual. If a left turn deceleration is not warranted, a left turn storage lane should be provided. Normally, left-turn lanes are designed as parallel lanes. Left Turn Deceleration Lane Warrants The basic guidelines for when left turn deceleration lanes are warranted involve mainline turning and approach volume, and intersection location. Turning and approach volume A left turn deceleration lane may be warranted if left turning traffic flow rate is greater than 30 vehicles per hour measured over a minimum of 15 minutes and either: a. approach volume is greater than 400 vehicles per hour, or b. approach truck traffic volume is greater than 40 vehicles per hour. Intersection location Intersection location may warrant a left turn deceleration lane even if turning and approach volumes do not. To improve operational efficiency, left turn deceleration lanes should be considered for intersections located within approximately 5 miles (8 kilometers) of an urban area with a population of 20,000 or greater. Other locations where left turn deceleration lanes may be judged to be warranted by the PMT include schools, main entrances for towns, shopping areas, housing developments, attraction locations such as recreational areas, and locations that would have special users such as truck traffic or campers. Special attention should be given to intersections serving locations that attract elderly drivers such as drug stores, grocery stores, retirement developments, medical facilities, nursing homes, etc. Entrance Types Type “A” entrance. An entrance developed to carry sporadic or continuous heavy concentrations of traffic. Generally, a Type “A” entrance carries in excess of 150 vehicles per hour. An entrance of this type would normally consist of multiple approach lanes and may incorporate a median. Possible examples include racetracks, large industrial plants, shopping centers, subdivisions, or amusement parks. Type “B” entrance. An entrance developed to serve moderate traffic volumes. Generally, a Type “B” entrance carries at least 20 vehicles per hour but less than 150 vehicles per hour. An entrance of this type would normally consist of one inbound and one outbound traffic lane. Possible examples include service stations, small businesses, drive-in banks, or light industrial plants. Type “C” entrance. An entrance developed to serve light traffic volumes. Generally, a Type “C” entrance carries less than 20 vehicles per hour. An entrance of this type would not normally accommodate simultaneous inbound and outbound vehicles. Possible examples include residential, farm or field entrances.

30 Table 17. South Dakota (50) introduction material and criterion 1. TURN LANE WARRANTS Left-turn lane Criteria — Unsignalized Intersections Left-turn lanes should be provided where through and turning volumes create an operational or a potential accident problem. Left-Turn Lane Evaluation Process • A left-turn lane should be installed if Criteria 1 (Volume), or 2 (Crash), or 3 (Special Cases) are met, unless a subsequent evaluation eliminates it as an option; and • The left-turn lane complies with access management spacing standards; and • The left-turn lane conforms to applicable local, regional and/or state design guidelines. Criterion 1: Vehicular Volume The vehicular volume criterion is intended for application where the volume of intersecting traffic is the principal reason for considering installation of a left-turn lane. The volume criteria are determined by the Texas Transportation Institute (TTI) curves in Figure 12-11. Note: The criterion is not met from zero to ten left turn vehicles per hour, but careful consideration should be given to installing a left-turn lane due to the increased potential for accidents in the through lanes. While the turn volumes are low, the adverse safety and operational impacts may require installation of a left turn. The final determination will be based on a field study. Figure 12-11 Left-Turn Lane Warrants

31 Table 18. South Dakota (50) criterion 2 and 3 and evaluation guidelines. Criterion 2: Crash Experience The crash experience criteria are satisfied when: 1. A history of crashes of the type susceptible to correction by a left-turn lane (such as a vehicle waiting to make a left turn from a through lane was struck from the rear). A separate left-turn lane may be warranted if five or more reported intersection related accidents occur within a 12 month period; and 2. The safety benefits outweigh the associated improvement costs; and 3. The installation of the left-turn lane does not adversely impact the operations of the roadway. Criterion 3: Special Cases 1. Railroad Crossings: If a railroad is parallel to the roadway and adversely affects left turns, a worst case scenario should be used in determining the storage requirements for the left-turn lane design. The left-turn lane storage length depends on the amount of time the side road is closed, the expected number of vehicle arrivals and the location of the crossing or other obstruction. The analysis should consider all of the variables influencing the design of the left-turn lane, and may allow a design for conditions other than the worst case storage requirements, provided safety is not compromised. 2. Geometric/Safety Concerns: Consider sight distance, alignment, operating speeds, nearby access movements and other safety related concerns. 3. Non-Traversable Median: A left-turn lane should be installed for any break in a non-traversable median where left turns are not prohibited. Evaluation Guidelines 1. The evaluation should indicate the installation of a left-turn lane will improve the overall safety and/or operation of the intersection and the roadway. If these requirements are not met, the left-turn lane should not be installed or, if already in place, removed from operation 2. Alternatives Considered: List all alternatives that were considered, including alternative locations. Briefly discuss alternatives to the left-turn lane considered to diminish congestion/delays resulting in criteria being met. 3. Access Management: Address access management issues such as the long term access management strategy for the roadway, spacing standards, other accesses that may be located nearby, breaks in barrier/curb, etc. 4. Land Use Concerns: Include how the proposed left-turn lane addresses land use concerns and transportation plans. 5. Plan: Include a design plan layout of the location of the proposed left-turn lane. 6. Operational Requirements: Consider storage length requirements, deceleration distance, desired alignment distance, etc. Chapter 5: At-Grade Intersections of Minnesota’s Road Design Manual (48) discusses left-turn lane policies. Similar to other design manuals, the document discusses where left-turn lanes should be provided (see Table 19). Criteria are presented for urban highways, multilane highways, and two-lane rural highways. For two-lane rural highways, left-turn lanes should be provided when the access is to a public road, an industrial tract, or a commercial center.

32 Table 19. Minnesota (48) left-turn material. 5-3.01.01 Turn Lane Policy at Urban Intersections Because of the operational and safety benefits associated with right and left-turn lanes, it is Mn/DOT’s policy that, in urban areas, they be considered wherever construction is economically feasible taking into account amount of right of way needed, type of terrain, and environmentally or culturally sensitive areas. For new construction/reconstruction projects on divided highways, left-turn and right-turn lanes should be considered at all locations where a paved crossover will be constructed. For preservation projects, left-turn lanes should, if feasible, be provided: 1. At all public road median crossovers. 2. At non-public access locations generating high traffic volumes. 3. At locations where accident records confirm the existence of an excessive hazard. 4. At locations determined by the District Traffic Engineer in consideration of accidents, capacity and traffic volumes. 5. Where a median opening is planned or exists, and its continued existence is justified, a left-turn lane may be added regardless of what the access point serves. 5-4.01 Turn Lanes As with urban highways, the degree of access control greatly influences the accident rate and efficiency of traffic operation on rural highways. Therefore, designers should try to close any unjustified or potentially dangerous access points. However, if an access point is to remain open, adding a turn lane will enhance the operation and safety. 1. In addition to the policies listed below, left-turn and right-turn lanes should be constructed at locations determined by the District Traffic Engineer in consideration of accidents, capacity, and traffic volumes. 2. Where a median opening is planned, or already exists and its continued existence is justified, a left-turn lane may be added regardless of what the access point serves. 3. Turn lanes should be considered at every public road intersection along a stretch of highway if most intersections on the stretch meet the warrants. If most intersections have turn lanes, motorists will come to expect all intersections to have them. 5-4.01.01 Policy on Multi-Lane Highways 1. Right-turn and left-turn lanes should be standard features at all public access points. 2. Right-turn and left-turn lanes are also warranted if the access point serves an industrial, commercial, or any substantial trip-generating land use, or if the access point serves more than three residential units. 5-4.01.02 Policy on two-lane Rural Highways 1. Right-turn lanes should be considered when the projected ADT is over 1500, the design speed is 45 mph or higher, and the following: a. At all public road access points. b. If industrial, commercial, or substantial trip generating land use is to be served, or c. If the access serves more than 10 residential units. 2. Left-turn lanes should be provided when the access is to a public road, an industrial tract or a commercial center. 3. The designer, in conjunction with the District Traffic Engineer may select either a channelized or a painted left-turn lane. The selection will be based on a number of factors including accident history, traffic volume, comparative costs, availability of right of way, environmental impacts, and physical features such as sight distance. Minnesota’s Mn/DOT Access Management Manual (52) also provides warrants for turn lanes. Turn lanes are to be provided at public street connections and driveways in accordance with the Mn/DOT Road Design Manual, Section 5-3, and the guidance provided in the Access Management Manual. Guidance provided includes the following: • Warrant 7: Crash History—at high-volume driveways (> 100 trips per day) and all public street connections that demonstrate a history of crashes of the type suitable to correction by a turn lane or turn-lane treatment (typically three or more correctable crashes in one year), or where adequate trial of other remedies has failed to reduce the crash frequency.

33 • Warrant 8: Corridor Crash Experience—on highway corridors that demonstrate a history of similar crash types suitable to correction by providing corridor-wide consistency in turn-lane use. • Warrant 9: Vehicular Volume Warrant—at high-volume driveways (> 100 trips per day) and all public street connections on high-speed highways (posted speed ≥ 45 mph) that satisfy the criteria in Table 20. Table 20. Minnesota Mn/DOTAccess Management Manual (52) warrant for left-turn lanes. Two-Lane Highway ADT Four-Lane Highway ADT Cross-Street or Driveway ADT Turn-Lane Requirement 1500 to 2999 3000 to 3999 4000 to 4999 5000 to 6499 ≥ 6500 ≥ 6500 3000 to 5999 6000 to 7999 8000 to 9999 10,000 to 12,999 ≥ 13,000 ≥ 13,000 > 1500 > 1200 >1000 > 800 100 to 400 ≥ 400 Left-turn lane warranted Left-turn lane warranted Left-turn lane warranted Left-turn lane warranted Left-turn or bypass lane warranted Left-turn lane warranted Highway AADT one year after opening. Posted speed 45 mph or greater. The Nevada Access Management System and Standards (23) presents the values provided in the Green Book for two-lane roads. The document also has criteria for multilane undivided (see Table 21) and divided (see Table 22) roads. The tables list the projected 20-year design-hour volumes (DDHV) of traffic “which necessitate the installation of left turn lanes.” Table 21. Nevada (23) left-turn lane requirements for multilane roads (unsignalized). Opposing Volume (DDHV) Advancing Volume (DDHV) for Left-Turn Percentages of: 5% 10% 20% 30% 800 600 400 200 100 140 220 350 530 650 110 160 250 380 480 80 120 190 290 350 70 100 160 250 310 Table 22. Nevada (23) left-turn lane requirements for multilane divided roads (unsignalized). Opposing Volume (DDHV) Advancing Volume (DDHV) for Left-Turn Percentages of: 5% 10% 20% 30% 800 600 400 200 100 210 340 520 800 1000 150 240 380 580 720 110 180 290 440 550 100 150 250 390 480

34 Financial Consideration The Minnesota design manual also uses the term “economically feasible,” which is a concept not discussed in most manuals. The Georgia manual mentions costs in association with left-turn lanes. Specific Offices within the Department of Transportation Three states’ manuals state that agencies within the department make the decision. For example, the Arizona Roadway Design Guidelines (53) states: “Traffic Engineering Group will analyze the traffic movements and other factors at an intersection to determine the need for a separate left- turn lane(s) and establish the vehicle storage requirements for the lane(s).” The California Highway Design Manual in Chapter 400: Intersections at Grade (54) states: “The District Traffic Branch normally establishes the need for left-turn lanes.” Minnesota (52) states: “Left-turn and right-turn lanes should be constructed at locations determined by the District Traffic Engineer in consideration of accidents, capacity, and traffic volumes.” No Information During this review, the research team did not find information on left-turn warrants in online documents for Hawaii, Idaho, Kansas, Maine, Maryland, Michigan, New Hampshire, North Carolina, North Dakota, Oklahoma, Rhode Island, South Carolina, Vermont, West Virginia, Wisconsin, or Wyoming. The research team did not find online manuals for Alabama or Arkansas. RIGHT-TURN LANE INSTALLATION GUIDELINES Several studies have addressed warrants for the installation of right-turn lanes. The methodology used to develop warrants for right-turn lanes may have application to the development of warrants for left-turn lanes. Guidelines Based on Volume NCHRP Report 279 (10) provides a summary of the current (mid-1980s) practice in providing exclusive right-turn lane (see Table 23). The report notes: No specific warrants or guidelines are apparent for low speed, urban intersections. Engineers generally rely on capacity analyses and accident experience when considering right-turn lanes. In rural areas, focus is primarily on a combination of through and right-turning volume.

35 Table 23. Summary of state design practice in providing right-turn lanes on rural highways (10). State Condition Warranting Right-Turn Lane off Major (Through) Highway Through Volume Right-Turn Volume Highway Conditions Alaska NA DHV = 25 veh/hr Not provided Idaho DHV = 200 veh/hr DHV = 5 veh/hr 2 lane Michigan NA ADT = 600 veh/day 2 lane Minnesota ADT = 1500 vpd All Design speed > 45 mph Utah DHV = 300 veh/hr ADT = 100 veh/day 2 lane Virginia DHV = 500 DHV = 40 mph 2 lane All DHV = 120 veh/hr Design speed > 45 mph DHV = 1200 veh/hr DHV = 40 veh/hr 4 lane All DHV = 90 veh/hr 4 lane West Virginia DHV = 500 veh/hr DHV = 250 veh/hr Divided highway Wisconsin ADT = 2500 veh/day Crossroad ADT = 1000 veh/day 2 lane DHV = design hourly volume ADT = average daily traffic NA = not applicable Guidelines Based on Risk Yang (55) presented a methodology for establishing volume warrant conditions for free right- turn lanes on two-lane roadways based on a risk probability of a potential rear-end crash involving a decelerating right-turn vehicle and the immediately following advancing through volume. Yang developed an equation that can be used to calculate the total approach volume when a free right-run lane on a two-lane roadway is warranted. The equation is a function of: • Time required to avoid possible rear-end crash: o Brake reaction time to surprise event (assumed 1.5 sec), o Turning speed of right-turn vehicle (assumed 10 mph), o Operating speed of advancing through vehicles, and o Uniform deceleration rate (assumed 11.2 ft/sec2); • Percent of right turns in total approach volume; • Minimum headway (assumed 0.66 sec); and • Risk probability (assumed 0.05). τ τ +       − − − − = )1( 1ln 3600 RR P t V r C (1) a sst trc − ×+= 278.05.1 (2)

36 Where: V = total approach volume (veh); tc = time required to avoid possible rear-end crash (sec); sr = operating speed of advancing through vehicles (km/h [1.0 mph = 1.6 km/h]); st = turning speed of right-turn vehicles (km/h) (assumed to be 16 km/h [10 mph]); a = uniform deceleration rate (m/sec2) (assumed to be 3.4 m/sec2 [11.2 ft/sec2]); τ = minimum headway (sec) (assumed to be 0.66 sec); Pr = risk probability, i.e., the probability of having a less-than-tc arrival interval between a right-turning vehicle and its immediately following advancing through vehicle (assumed to be 0.05); and R = percent of right turns in the total approach volume. The limiting probabilities of a through vehicle arriving behind a stopped left-turning vehicle assumed in the Harmelink model are 0.02 for 40 mph, 0.015 for 50 mph, and 0.010 for 60 mph. Yang argues that these values may not be appropriate because a right-turn vehicle does not come to a complete stop and await an acceptable gap in the opposing traffic stream as a left-turn vehicle does and will clear the travel lane in an expectedly short time period. Therefore, he recommends a higher limiting risk probability of 0.05. Using the 0.05 value, he developed a set of warrant curves. Yang’s proposed risk probability was evaluated using data available in a previous NCHRP study, and a fair agreement was found between the assumed risk probability and the observed percent of through vehicles impacted by right-turn vehicles. If an agency prefers different assumptions, for example the minimum headway, Yang’s equation can be used to determine the warrants for that area. Guidelines Based on Benefit/Cost Glennon et al. (56) conducted a benefit/cost analysis of right-turn lanes at driveways. The results of the analysis indicated that right-turn lanes are cost-effective at driveways when the driveway volume is at least 1000 veh/day with at least 40 right turns in the driveway during peak periods, the roadway average daily traffic is at least 10,000 veh/day, and the roadway speed is at least 35 mph. McCoy et al. (57) developed guidelines for the use of right-turn lanes at access points on urban two-lane and four-lane roadways. The guidelines define the design-hour traffic volumes for which the benefits of right-turn lanes exceed their costs. The benefits used in the analysis are the operational and accident cost savings that right-turn lanes provide road users. The operational cost savings are those associated with the reductions in stops, delays, and fuel consumption experienced by through traffic as determined through simulation. The guidelines define the right- turn design-hour volume required to justify a right-turn lane as a function of the following factors: • Directional design-hour volume, • Roadway speed, • Number of lanes on the roadway, and • Right-of-way costs.

37 Potts et al. (58) in 2007 described economic-analysis procedures that identify unsignalized intersections and major driveways at which provision of right-turn lanes is cost-effective. Table 24 shows the equation used in the evaluation. Table 24. Potts et al. (58) equation used to determine benefit/cost ratio. ( )[ ] CC niUSPWFACnAMFVVAFDCnKVVDRCB RTRTTRTT ),()1(),(),,(/ ×××−×+××= (3) n n ii iniUSPWF )1( 1)1(),( + −+ = (4) Where: B/C = benefit-cost ratio; DR(VT, VRT, K) = delay reduction (veh-sec/hr) from right-turn lane installation as a function of VT, VRT, and K; VT = peak-hour through traffic volume (veh/hr) on the major road; VRT = peak-hour volume turning right at the location in question (veh/hr); K = design-hour factor, the percentage of ADT during the peak hour; n = service life of right-turn lane (year); DC = user cost savings from delay reduction ($/veh-hr); AF(VT, VRT) = expected accident frequency (accidents/year) at location of interest with no right-turn lane present as a function of VT and VRT; AMFRT = accident modification factor for right-turn lane installation; AC = user cost savings from accident reduction ($/accident); USPWF(i,n) = uniform series present-worth factor as a function of i and n (see above equation); i = minimum attractive rate of return expressed as a decimal (i.e., 0.04 for a 4 percent return); and CC = estimated construction cost ($) for a right-turn lane. The operational effects were determined using a computer simulation study of motor vehicles and pedestrians at right-turn lanes. Table 25 lists the delay reductions found for two-lane arterials, and Table 26 lists the delay reductions for four-lane arterials. The estimated reduction in delay to through vehicles provided by a right-turn lane typically ranged from 0 to 6 sec/through veh. The delay reduction is more pronounced as the mainline speeds, through volumes, and right-turn volumes increase. Pedestrian activity at unsignalized intersections and driveways can have a substantial impact on delay to through vehicles due to right-turning vehicles having to yield to pedestrians. The findings by Potts et al. found delay deductions ranging between 0.4 and 6.0 sec/through veh. Table 27 lists the delay reductions. The delay values listed in Table 25 to Table 27 are expressed on an hourly basis. To expand these estimates from a single-hour period to an entire year, assumptions were made about the distribution of traffic on typical weekdays and typical weekend days. Table 28 shows an example

38 for a site with a peak-hour through volume of 2200 veh/hr and a peak-hour right-turn volume of 220 veh/hr. The service life of the right-turn lane was assumed to be 20 years. For the analysis, $9.00 per hour (or 50 percent of the U.S. average wage) was used. Table 25. Potts et al. (58) delay reduction provided by provision of a right-turn lane on a two-lane arterial (sec/through veh). Speed (mph) Through Volume (veh/hr) Right-Turn Volume (veh/hr) 0 50 100 150 200 250 300 35 0 200 400 600 800 1000 1200 1400 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.1 0.2 0.2 0.2 0.2 0.3 0.4 0.0 0.2 0.4 0.4 0.4 0.5 0.6 0.9 0.0 0.3 0.5 0.6 0.6 0.8 1.0 1.6 0.0 0.4 0.7 0.8 0.9 1.2 1.5 2.3 0.0 0.5 0.9 1.0 1.1 1.6 2.1 3.2 0.0 0.5 1.1 1.1 1.4 2.1 1.8 4.3 45 0 200 400 600 800 1000 1200 1400 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.2 0.3 0.3 0.4 0.4 0.5 0.6 0.0 0.3 0.6 0.6 0.7 0.9 1.0 1.2 0.0 0.5 0.9 1.0 1.1 1.3 1.6 1.8 0.0 0.6 1.2 1.3 1.5 1.8 2.2 2.5 0.0 0.8 1.6 1.6 1.9 2.3 2.8 3.3 0.0 0.9 1.9 1.9 2.3 2.9 3.5 4.0 55 0 200 400 600 800 1000 1200 1400 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.2 0.4 0.5 0.5 0.6 0.7 0.9 0.0 0.4 0.9 0.9 1.0 1.2 1.4 1.8 0.0 0.7 1.3 1.4 1.6 1.9 2.1 2.8 0.0 0.9 1.7 1.9 2.1 2.5 2.8 3.8 0.0 1.1 2.2 2.3 2.6 3.1 3.6 4.9 0.0 1.3 2.6 2.8 3.1 3.7 4.3 6.1

39 Table 26. Potts et al. (58) delay reduction provided by provision of a right-turn lane on a four-lane arterial (sec/through veh). Speed (mph) Through Volume (veh/hr) Right-Turn Volume (veh/hr) 0 50 100 150 200 250 300 350 400 35 0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.1 0.1 0.1 0.1 0.0 0.0 0.0 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.0 0.0 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.2 0.2 0.2 0.0 0.0 0.1 0.1 0.1 0.1 0.2 0.2 0.2 0.2 0.2 0.3 0.0 0.0 0.1 0.1 0.1 0.2 0.2 0.2 0.2 0.3 0.3 0.3 0.0 0.1 0.1 0.2 0.2 0.2 0.2 0.3 0.3 0.3 0.4 0.4 0.0 0.1 0.1 0.2 0.2 0.2 0.3 0.3 0.3 0.4 0.4 0.2 0.0 0.1 0.1 0.2 0.2 0.3 0.3 0.3 0.4 0.4 0.5 0.6 45 0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.1 0.1 0.1 0.1 0.1 0.0 0.0 0.0 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.2 0.2 0.0 0.0 0.1 0.1 0.1 0.1 0.1 0.2 0.2 0.2 0.2 0.2 0.0 0.0 0.1 0.1 0.1 0.2 0.2 0.2 0.2 0.3 0.3 0.3 0.0 0.1 0.1 0.1 0.2 0.2 0.2 0.3 0.3 0.3 0.4 0.4 0.0 0.1 0.1 0.2 0.2 0.2 0.3 0.3 0.4 0.4 0.4 0.5 0.0 0.1 0.1 0.2 0.2 0.3 0.3 0.4 0.4 0.5 0.5 0.6 0.0 0.1 0.2 0.2 0.3 0.3 0.4 0.4 0.5 0.5 0.6 0.6 55 0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.1 0.1 0.1 0.1 0.1 0.1 0.0 0.0 0.0 0.1 0.1 0.1 0.1 0.1 0.1 0.2 0.2 0.2 0.0 0.0 0.1 0.1 0.1 0.1 0.2 0.2 0.2 0.2 0.3 0.3 0.0 0.1 0.1 0.1 0.2 0.2 0.2 0.3 0.3 0.3 0.4 0.4 0.0 0.1 0.1 0.1 0.2 0.2 0.3 0.3 0.3 0.4 0.4 0.5 0.0 0.1 0.1 0.2 0.2 0.3 0.3 0.4 0.4 0.5 0.5 0.6 0.0 0.1 0.1 0.2 0.2 0.3 0.45 0.4 0.5 0.5 0.6 0.7 0.0 0.1 0.2 0.2 0.3 0.3 0.4 0.5 0.5 0.6 0.7 0.8

40 Table 27. Potts et al. (58) additional delay reduction provided by right-turn lane where pedestrian activity is present (sec/through veh). Pedestrian Activity Level (ped/hr) Right-turn Volume (veh/hr) Through Volume (veh/hr) 400 600 800 1200 50 100 200 0.4 0.9 0.5 1.0 0.6 1.3 0.9 2.1 100 100 200 0.6 1.2 0.6 1.3 0.7 1.5 1.3 3.1 200 100 200 0.8 1.7 0.9 2.1 1.1 2.5 2.2 6.0 Table 28. Potts et al. (58) example of how annual delay reduction benefit was calculated. Period Number of Hours in Weekday (Weekend) Hourly (Total) Percent of ADT Traffic Volumes in the Direction of the Right- Turn Lane (veh/hr) Delay Reduction (sec/ through veh) Number of Hours per Year Annual Delay Reduction Benefit (veh- sec/year) Through Right Turn AM peak PM peak Off-Peak Evening Night 2 (0) 2 (0) 5 (9) 7 (7) 8 (8) 10.0 (20.0) 10.0 (20.0) 5.8 (29.0) 2.6 (18.2) 1.6 (12.8) 2200 2200 1276 572 352 220 220 127 57 35 0.42 0.42 0.13 0.03 0.01 522 522 2241 2555 2920 493,812 493,812 386,607 47,817 12,735 Total (24 Hours) 24 (24) (100) 22,000 2,200 8,760 1,434,783 The annual accident frequency for an unsignalized intersection was estimated from safety performance functions (SPFs) developed for FHWA’s Safety Analyst project as stated in its work on right-turn lanes (58). The SPFs used in the analysis are listed in Table 29. The safety benefits are based on a study by Harwood et al. (2) that developed accident modification factors (AMFs) for the installation of right-turn lanes on major-road approaches to rural and urban intersections (see Table 30). The data used to compute accident cost savings are presented in Table 31. The cost of constructing a right-turn lane was estimated as $100,000. The authors note that this is a conservative value, which should assure that the analysis results are not overly optimistic.

41 Table 29. Potts et al. (58) equations for predicting accident frequency. Intersection Type Equations Three-leg intersections with minor-road STOP control AF = 0.00475 (ADTmajor)0.34 (ADTminor)0.28 ADTmajor = (2VT + 2VRT)/K ADTminor = 2VRT (5) (6) (7) Four-leg intersection with minor-leg STOP control AF = 0.0442 (ADTmajor)0.27 (ADTminor)0.16 ADTmajor = (2VT + 2VRT)/K ADTminor = 4VRT (8) (9) (10) Where: AF = annual accident frequency for unsignalized intersection or driveway, ADTmajor = average daily traffic volume (veh/day) of the major road (i.e., the road on which the right-turn lane is installed, ADTminor = average daily traffic volume (veh/day) on the minor leg of the intersection, VT = peak-hour through traffic volume (veh/hr) on the major road, VRT = peak-hour volume turning right at location in question (veh/hr), and K = design-hour factor, the percentage of ADT during the peak hour. Assumptions: • While the SPFs were developed for unsignalized intersections, they are also considered appropriate for application to unsignalized driveways. • Traffic volumes in both directions of travel on the major road are the same. • The right-turn volume from the minor road onto the major road is the same as the right- turn volume from the major road onto the minor road that uses the right-turn lane of interest. • The left-turn volumes entering and leaving the major road are the same as the right-turn volumes. • At four-leg intersections the turning volumes to and from the minor road are the same on both sides of the major roads. • At four-leg intersections there is no crossing traffic between the minor-road legs. Table 30. Potts et al. (58) accident modification factors for right-turn lanes. Intersection Traffic Control Number of Major-Road Approaches on Which Right-Turn Lanes Are Installed One Approach Both Approaches Stop Sign on Minor Road Traffic Signal 0.86 0.96 0.74 0.92

42 Table 31. Accident cost and severity distributions (58). Accident Severity Cost per Accident Accident Severity Distribution (%) 3-Leg Intersection 4-Leg Intersection Fatal Accident A Injury Accidents B Injury Accidents C Injury Accidents Property Damage Only (PDO) Accidents $3,300,000 $228,000 $46,000 $24,000 $2,500 0.2 1.4 11.9 21.5 65.0 0.4 2.5 11.7 20.5 64.9 Accident cost $22,000 $31,000 Guidelines Based on a Combination of Approaches Hai and Thakkar (59) developed criteria for right-turn lanes based on speed differential in the outside lane caused by right-turning vehicles. Simulation provided an estimate of the affected through volume in the outside lane and the drop in speed for combinations of outside-lane through movement volume, right-turning volume, and through movement speed. These results were used to derive the critical right-turn volumes as shown in Table 32. Also considered was an assumed relationship between the magnitude of speed deviation and crashes. Critical right-turn volumes were estimated at two levels of benefit-cost ratios. In their study, a benefit-cost ratio of 2.2 was assumed to be associated with a savings of three crashes per year. The 1.5 benefit-cost ratio represents a saving in crashes of 2.2 per year. Table 32. Hai and Thakkar (59) critical right-turn volumes for different operating speeds. Total Volume (veh/hr) Critical Right-Turn Volume (veh/hr) B/C = 2.2 B/C = 1.5 B/C = 2.2 B/C = 1.5 B/C = 2.2 B/C = 1.5 B/C = 2.2 B/C = 1.5 B/C = 2.2 B/C = 1.5 Speed (mph): 35 35 40 40 45 45 50 50 55 55 400 500 600 700 800 900 1000 175 150 125 105 90 80 70 120 100 80 65 60 50 45 150 125 100 80 70 60 55 100 80 60 50 45 40 35 120 95 75 60 53 45 40 70 50 40 35 30 27 25 75 65 55 45 40 35 30 55 45 35 30 25 23 20 60 50 40 35 30 27 23 40 30 25 22 20 17 15 B/C = benefit/cost ratio