Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
50 Description A right-turn lane is an auxiliary lane provided to allow right-turning vehicles to conduct most of their deceleration and, if necessary, queue before making their turn. The technique of widening the right through lane to better accommodate right turns from driveways is also included as part of this group. A continuous right-turn lane should not be longer than one- quarter mile to avoid additional conflicts when there is both vehicular and bicycle traffic (1). Tables 36 through 39 follow. Quantitative Analysis Methods Motor Vehicle Operations Chapter 19 in the HCM6 can be used to compare the change in delay as a result of installing right-turn lanes at signalized intersections (4), in cases where the right-turn lane is adequately sized to prevent queue spillback into the through lanes. Simulation of right-turn delays at unsignalized (i.e., minor street stop-controlled) inter- sections on two-lane arterials found that right-turning-vehicle delay to through vehicles ranged from 0 to 6 seconds (2). The highest delay occurred with a high speed limit (55 mph), high through volumes (1,400 vehicles per hour), and high right-turn volumes (500 vehicles per hour). Delays on 4-lane arterials under the same conditions were in the range of 0â1 second. When pedestrians were present on the parallel crosswalk causing right-turning traffic to yield C H A P T E R 1 0 Right-Turn Lanes Source: Photograph provided by the authors.
Right-Turn Lanes 51 Access Management Technique Performance Trends and Documented Performance Relationships Operations Safety Install right-turn deceleration lanes where none exists. â â â â â â â â â â Â Â Â Â Â Â Â Â Â Â Install continuous right-turn lane. â â â â â â â â â Â Â Â Â Â Â Widen right through lane to limit encroachment on adjacent lane from right-turn egress vehicles. Â â â Â Â â â â Â Â Â Â Â Â Â Â Â Â Â Table 36. Multimodal operations and safety performance summary. Motor vehicle free-flow and travel speeds increase by up to a few miles per hour. Speed increases are greater when only one through travel lane is available and with higher through traffic volumes, higher turning traffic volumes, and higher pedestrian volumes on the parallel crosswalk (2). The motorized vehicle crash rate decreases (3). With continuous right-turn lanes, however, drivers exiting driveways may experience confusion about where approaching vehicles plan to turn. Widening the rightmost travel lane provides more space for large vehicles to turn onto the roadway without encroaching on the adjacent lane. Small negative effect on pedestrian LOS due to increased motor vehicle speeds (4, 5). At unsignalized intersections, crossing distance and pedestrian delay increase and pedestrian LOS may decrease (4, 6). The traffic signal cycle length may need to increase to accommodate longer pedestrian crossing distances, increasing pedestrian delay (6). Widening the rightmost travel lane increases the separation of traffic from the sidewalk, improving pedestrian LOS (4, 5). May increase vehicleâpedestrian crash frequency if not channelized (2, 7). Increases pedestrian exposure to traffic when crossing the major road, due to the widened roadway (6). Visually impaired pedestrians may experience difficulty crossing the driveway or minor street, as sound from through vehicles may mask the sound of a decelerating conflicting vehicle in the right-turn lane (8). Small reduction in bicycle delay (9). Higher vehicle speeds lower bicycle LOS (4, 5). Widening the rightmost travel lane improves bicycle LOS (4, 5). Increases cross-street bicycle exposure to traffic due to widened cross-section (6). Requires consideration of vehiclesâ weaving maneuver into the right-turn lane (6, 10). A wider right- hand travel lane increases separation from motorized vehicles (3). Small increase in bus delay when a near-side bus stop is provided at a traffic signal (9). Without a near-side stop, bus benefits are similar to, but greater than, motor vehiclesâ benefits because buses accelerate more slowly to their running speed after stopping or slowing (11). At traffic signals, provides the potential for a queue jump or bypass (12). May constrain where bus stops can be located, require bus exemptions from right- turn-only requirements, or both (12). Substantially increases conflicts between buses serving near-side stops and both right-turning and through vehicles (9). Conflicts with right- turning vehicles further increase when the bus stop is located prior to the stop bar or corner (12). Motor vehicle effects also apply to buses. Similar to motor vehicles, but with greater benefit for trucks, as they accelerate more slowly to their running speed after stopping or slowing (13). Improved truck LOS due to improved speeds (14). Slightly reduces conflicts between trucks and other vehicles, with the effect greater with increasing turn-lane length (9). Motor vehicle effects also apply to trucks. Mode Operations Safety Table 37. General trends associated with providing right-turn lanes.
52 Guide for the Analysis of Multimodal Corridor Access Management to them, through traffic experienced an additional 0â6 seconds of delay, with the highest delay occurring with high through volumes (1,200 vehicles per hour), high right-turn volumes (200 vehicles per hour), and high pedestrian volumes (200 pedestrians per hour). Chapter 31, Section 4, in the HCM6 can be used to calculate a desired percentile back-of- queue for right-turn lanes at signalized intersections (4). A taper distance, allowing vehicles to maneuver from the through lane into the left-turn lane, and a deceleration distance need to be added to this storage length when determining the total left-turn lane length. Equation 16-2 in the Access Management Manual, Second ed. (10) can estimate the minimum storage distance for a right-turn lane. Workbook 12 that accompanies the linked version of the Access Management: Manual and Application Guidelines (15) is a spreadsheet tool for calculating the total right-turn lane length at signalized intersections. Motor Vehicle Safety The HSM provides crash modification factors related to installing right-turn lanes on the major street approaches to stop-controlled intersections and on any approach to a signalized intersection (3) (see Table 38 above). Intersection Type Traffic Volume: AADT (vehicles per day) Crash Severity Crash Modification Factor by Number of Approaches with Right-Turn Lanes One Approach Two Approaches Urban or rural, minor road stop-controlled Major: 1,500â40,600 Minor: 25â26,000 All 0.86 0.74 Injury 0.77 â Unspecified Injury â 0.59 Urban or rural, signalized Major: 7,200â55,100 Minor: 550â8,400 All 0.96 0.92 Injury 0.91 â Unspecified Injury â 0.83 Note: Values apply to major street approaches at unsignalized intersections and any approach at signalized intersections. For signalized intersections with three or four approaches with right-turn lanes, the crash modification factor is the value for one approach raised to the third or fourth power, respectively. A dash indicates no crash modification factor provided for this combination of number of approaches, crash severity, and AADT. There are intersection types associated with an unspecified AADT, as shown in the table (either minor road stop controlled, or signalized). The Highway Safety Manualâs crash modification factors for injury crashes when one approach has a right-turn lane were developed by using data from sites with AADTs within the range given in the table. The studies used to develop crash modification factors in situations where two approaches had right-turn lanes did not specify the AADTs associated with the study sites. Source: Highway Safety Manual, 1st ed., Tables 14-15 and 14-16 (3). Table 38. Crash modification factors: Right-turn lanes. Speed Differential (mph) Crash Rate Ratio Relative to no Speed Differential 0 1.0 â10 2.0 â20 6.5 â30 45 â35 180 Source: Solomon (16), Stover and Koepke (17). Table 39. Crash rate ratios for various speed differentials on rural highways relative to no speed differential.
Right-Turn Lanes 53 Right-turn lanes that are too short to accommodate demand or that otherwise provide insuf- ficient deceleration distance result in a greater speed differential between right-turning vehicles and through vehicles relative to the typical design differential of 10 mph (1). Table 39 (16, 17) gives crash rate ratios for various speed differentials on rural highways, relative to no speed dif- ferential. For example, the crash rate with a 10-mph speed differential is twice the crash rate with no speed differential. Pedestrian Operations Equations 18-32, 18-33, and 18-35 in the HCM6 (4) can determine the effect of motorized vehicle speeds and rightmost travel lane width on pedestrian link LOS. An increase in average traffic speed of 2 mph worsens the pedestrian link LOS score by 0.03 points (at 20 mph) to 0.08 points (at 50 mph), with 0.75 points representing the range covered by one LOS letter. Increasing the rightmost lane width from 12 feet to 15 feet, assuming no parking or bicycle lane, and assuming a 6-foot curb-tight sidewalk, improves the pedestrian link LOS score by 0.10 points. Equation 19-72 in the HCM6 (4) can determine the effect of intersection width on pedestrian intersection LOS. An increase of one lane of width worsens the pedestrian intersection LOS score by 0.13 (widening from 7 to 8 lanes, including turn lanes) to 0.23 points (2 to 3 lanes), with 1.00 point representing the range covered by one LOS letter. Pedestrian Safety Potts et al. (7) developed a model for predicting the frequency of vehicleâpedestrian crashes associated with a signalized intersection approach. The model includes an input variable that describes the right-turn design type (i.e., no turn lane, turn lane without channelizing island, turn lane with channelizing island). The model indicates that the addition of a right-turn lane (without channelization) increases the frequency of crashes relative to either no turn lane or a channelized right-turn lane. See the appendix for more details about the model. Bicycle Operations Equations 18-41, 18-42, and 18-44 in the HCM6 (4) can determine the effect of motorized vehicle speed and rightmost travel lane width on bicycle link LOS. An increase in average traffic speed of 2 mph worsens the bicycle link LOS score by 0.57 points (at 21 mph or less), 0.17 points (at 25 mph), 0.05 points (at 40 mph), and 0.03 points (at 50 mph), with 0.75 points representing the range covered by one LOS letter. Increasing the rightmost lane width from 12 feet to 15 feet, assuming no parking or bicycle lane, improves the bicycle link LOS score by 0.41 points. Equation 19-80 in the HCM6 (4) can determine the effect of intersection width on bicycle intersection LOS. An increase in intersection width of 12 feet worsens the bicycle intersection LOS score by 0.18 points, with 1.00 point representing the range covered by one LOS letter. A simulation study (9) found that right-turn deceleration lanes reduced bicycle delay at traffic signals in the range of 0.6 to 3.1 seconds, depending on the traffic signal cycle length and on truck, bicycle, and automobile volumes. Bicycle Safety Carter et al. (18) developed a model to predict a safety index for bicycle intersection. The index value would worsen by 0.47 rating points when a right-turn lane was added to a street where a bicycle lane is present, due to the interaction of right-turning vehicular traffic crossing over the path of through bicyclists. See the appendix for more details about this model.
54 Guide for the Analysis of Multimodal Corridor Access Management Bus Operations A simulation study (9) found that right-turn deceleration lanes increased bus delay at near-side stops at traffic signals in the range of 0.6 to 4.1 seconds, depending on the right-turn lane length, traffic signal cycle length, bus dwell time length, and vehicular volumes. Bus Safety A simulation study (9) found that conflicts between vehicles and buses stopping at a near- side stop located at the stop bar at a signalized intersection more than doubled for typical right- turn lane lengths. Because the intersections for which the simulation models were calibrated showed a linear relationship between different types of modeled vehicleâvehicle conflicts and their associated types of crashes, it was concluded that the crash rate would change proportionately to the conflict rate. Crashes involving public transit buses are rare; thus, it is not possible to develop crash modification factors or CMFs for buses from field data. However, based on the simulated conflicts, the following CMF was developed for crashes involving buses, where a right-turn lane was added at a bus stop: e LRTCMFbus 1.096 0.00084= ( )â where LRT is the right-turn lane length in feet and e represents exponential. The CMF is 2.75 for a 100-foot right-turn lane and 2.32 for a 300-foot right-turn lane. Truck Operations Section P in Exhibit 3 of NCHRP Report 825 (19), derived from NCFRP Report 31 (14), can be used to estimate the effect of improved truck free-flow and travel speeds on overall truck LOS. On a level street with a 35-mph free-flow speed, increasing average truck speeds from 25 to 26 mph results in a 1.3 percentage point increase in the truck LOS index, while increas- ing average truck speeds from 17.5 to 18.5 mph results in a 7.0 percentage point increase, with 10 percentage points representing the range covered by one LOS letter. Truck Safety A simulation study (9) found that the number of conflicts between vehicles and trucks was reduced when a left-turn lane was provided. Because the intersections for which the simulation models were calibrated showed a linear relationship between different types of modeled vehicleâ vehicle conflicts and their associated types of crashes, it was concluded that the crash rate would change proportionately to the conflict rate. Based on the simulated conflicts, the following CMF was developed for crashes involving trucks when a right-turn lane was added at an intersection: CMFtruck 0.00027e LRT= â The CMF is 0.97 for a 100-foot right-turn lane and 0.92 for a 300-foot right-turn lane. Additional Information â¢ Chapter 11 in this guide. â¢ Access Management Manual, Second ed.: Chapter 16, Auxiliary Lanes, Sections 20.3.5 and 20.3.6. â¢ Access Management Application Guidelines: Chapter 22, Right-Turn Lanes.
Right-Turn Lanes 55 References 1. Gluck, J., and M. Lorenz. NCHRP Synthesis 404: State of the Practice in Highway Access Management. Transportation Research Board of the National Academies, Washington, D.C., 2010. 2. Potts, I., J. Ringert, D. Harwood, and K. Bauer. Operational and Safety Effects of Right-Turn Deceleration Lanes on Urban and Suburban Arterials. Transportation Research Record: Journal of the Transportation Research Board, No. 2023, 2007, pp. 52â62. 3. Highway Safety Manual, 1st ed. American Association of State Highway and Transportation Officials, Washington, D.C., 2010. 4. Highway Capacity Manual: A Guide for Multimodal Mobility Analysis, 6th ed. Transportation Research Board, Washington, D.C., 2016. 5. Dowling, R., D. Reinke, A. Flannery, P. Ryus, M. Vandehey, T. Petritsch, B. Landis, N. Rouphail, and J. Bonneson. NCHRP Report 616: Multimodal Level of Service Analysis for Urban Streets. Transportation Research Board of the National Academies, Washington, D.C., 2008. 6. Dixon, K. K., R. D. Layton, M. Butorac, P. Ryus, J. L. Gattis, L. Brown, and D. Huntington. Access Management Application Guidelines. Transportation Research Board, Washington, D.C., 2016. 7. Potts, I. B., D. W. Harwood, K. M. Bauer, D. K. Gilmore, J. M. Hutton, D. J. Torbic, J. F. Ringert, A. Daleiden, and J. M. Barlow. NCHRP Web-Only Document 208: Design Guidance for Channelized Right-Turn Lanes. Transportation Research Board of the National Academies, Washington, D.C., July 2011. 8. Potts, I. B., D. W. Harwood, D. J. Torbic, D. K. Gilmore, J. F. Ringert, C. B. Tiesler, D. L. Harkey, and J. M. Barlow. Synthesis on Right-Turn Deceleration Lanes on Urban and Suburban Arterials. NCHRP Project 03-72. Transportation Research Board of the National Academies, Washington, D.C., Aug. 2006. 9. Butorac, M., J. Bonneson, K. Connolly, P. Ryus, B. Schroeder, K. Williams, Z. Wang, S. Ozkul, and J. Gluck. Web-Only Document 256: Assessing Interactions Between Access Management Treatments and Multimodal Users. Transportation Research Board, Washington, D.C., 2018. 10. Williams, K. M., V. G. Stover, K. K. Dixon, and P. Demosthenes. Access Management Manual, Second ed. Transportation Research Board of the National Academies, Washington, D.C., 2014. 11. Hemily, B., and R. D. King. TCRP Synthesis 75: Uses of Higher Capacity Buses in Transit Service. Transporta- tion Research Board of the National Academies, Washington, D.C., 2008. 12. Ryus, P., K. Laustsen, K. Blume, S. Beaird, and S. Langdon. TCRP Report 183: A Guidebook on Transit-Supportive Roadway Strategies. Transportation Research Board, Washington, D.C., 2016. 13. Harwood, D. W., D. J. Torbic, K. R. Richard, W. D. Glauz, and L. Elefteriadou. NCHRP Report 505: Review of Truck Characteristics as Factors in Roadway Design. Transportation Research Board of the National Academies, Washington, D.C., 2003. 14. Dowling, R., G. List, B. Yang, E. Witzke, and A. Flannery. NCFRP Report 31: Incorporating Truck Analysis into the Highway Capacity Manual. Transportation Research Board of the National Academies, Washington, D.C., 2014. 15. Transportation Research Board. Access Management: Manual and Application GuidelinesâLinked. Transportation Research Board, Washington, D.C., 2017. 16. Solomon, D. H. Accidents on Main Rural Highways Related to Speed, Driver, and Vehicle. Bureau of Public Roads, Washington, D.C., 1964. 17. Stover, V. G., and F. J. Koepke, Transportation and Land Development, 2nd ed., Institute of Transportation Engineers, Washington, D.C., 2002. 18. Carter, D. L., W. W. Hunter, C. V. Zegeer, J. R. Stewart, and H. F. Huang. Pedestrian and Bicyclist Intersection Safety Indices: Final Report. Report FHWA-HRT-06-125. Federal Highway Administration, Washington, D.C., Nov. 2006. 19. Dowling, R., P. Ryus, B. Schroeder, M. Kyte, T. Creasey, N. Rouphail, A. Hajbabaie, and D. Rhoades. NCHRP Report 825: Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual. Transportation Research Board, Washington, D.C., 2016.