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Chapter 4. Traffic Operational Analysis of Channelized Right-Turn Lanes This chapter presents the results of a traffic operational analysis of channelized right-turn lanes conducted with the VISSIM simulation model. The primary traffic operational reasons for providing channelized right-turn lanes are to increase vehicular capacity at an intersection and to reduce delay to drivers by allowing them to turn at higher speeds and reduce unnecessary stops. Channelized right-turn lanes appear to provide a net reduction in motor vehicle delay at intersections where they are installed, although no existing data and no established methodology have been available to directly compare the operational performance of urban intersections with and without channelized right-turn lanes. A traffic operational evaluation of channelized right-turn lanes, with and without pedestrian signals on the right-turn roadway, was conducted to quantify the differences between alternative designs. Four key questions related to traffic operations at channelized right-turn lanes were central to the traffic operational analysis. They are: ⢠What is the traffic operational performance of channelized right-turns lanes? ⢠What traffic operational benefits would be lost if channelized right-turn lanes were not used? ⢠What are the effects of different geometric designs of channelized right-turn lanes (location of crosswalk, turning radius, etc.) on traffic operational performance? ⢠What are the effects of traffic control strategies on the operation of channelized right- turn lanes? The answers to these questions play a key role in the decision of whether a channelized right-turn lane should be installed at an intersection. In order to answer these questions, the operational research focused on specific issues that could be addressed through the use of traditional traffic analysis modeling. These included: ⢠Impact of providing a channelized right-turn lane on traffic delay at various traffic volume levels ⢠Impact of pedestrians on signalized and unsignalized right-turn movements ⢠Impact of key design features on the operational performance of a channelized right-turn lane including: - Location of pedestrian crosswalk - Radius of channelized right-turn roadway - Speed of the cross-street onto which the right-turn vehicle is turning - Provision of acceleration and deceleration lanes - Effects of signal timing strategies 41
Traffic Operational Modeling 4.1 The majority of the traffic operational studies were performed using simulation modeling, which can test many design, traffic volume, and pedestrian volume combinations. Simulation modeling allows for the evaluation of vehicle-to-vehicle and vehicle-to-pedestrian interactions in a controlled environment. The traffic operational analysis was conducted to evaluate the traffic operational performance of right-turning vehicle movements at signalized intersections for three configurations (illustrated in Figure 15): a conventional right-turn lane at a signalized intersection, a yield-controlled channelized right-turn lane, and a signalized channelized right- turn lane. These configurations were chosen because they represent the most typical urban situations in which a channelize right-turn lane is either used or being considered for use. A series of microscopic simulation runs (using VISSIM) were conducted to evaluate the traffic operational performance for both vehicles and pedestrians. Three key simulation studies were performed for this evaluation: ⢠Right-turn vehicle delay: The impact of the right-turn volume and conflicting through volume on delay to the right-turning vehicle. ⢠Delay due to pedestrian crossings: The impact of pedestrian volume crossing the conflicting crosswalk on the delay to the right-turning vehicle. ⢠Impact of intersection characteristics: The changes in right-turn vehicle delay due to design of the channelized right-turn lane and different signal strategies, including: - Speed of vehicles on the cross street - Speed/radius of the right-turning movement - Effects of the a right-turn overlap phase for the signalized movements - Impacts of an acceleration lane on the delay to right turns 4.1.1 Modeling Configurations The three modeling configurations used for the simulation analysis are described and illustrated below. In order to reduce the number of variables that might affect the results of the analysis, many assumptions with respect to the intersection design were held constant. These included roadway approach speed, signal cycle length, and lane widths. In addition, the following assumptions were made for the right-turn lane: ⢠Approach speeds of 48 km/h (30 mi/h) ⢠Infinite storage in the subject right-turn lane ⢠Standard 3.6-m (12-ft) travel lanes ⢠A two-phase signal with a 90-second cycle and 50 percent of the time allocated to the right-turn phase 42
Each configuration is described below. Configuration 1 is a typical signalized intersection with a conventional (i.e., non- channelized) right-turn lane. The evaluation for this configuration focused on the delay for right-turning vehicles based on a range of right-turn volumes and conflicting through volumes. In addition, delay to right-turning traffic due to pedestrian crossings was evaluated. Configuration 2 is a typical signalized intersection with a yield-controlled channelized right-turn lane. The evaluation for this configuration focused on the delay to right-turning vehicles due to conflicting traffic on the cross street and pedestrians crossing the channelized right-turn lane. In addition, key geometric characteristics of the channelized right-turn lane (turning radius, location of crosswalk) were evaluated. Figure 15. Intersection Configurations for Traffic Operational Analysis 43
Configuration 3 assumes a signal-controlled channelized right-turn lane. The evaluation for this configuration focused on the differences in right-turn delay due to signalization of the right turn assuming similar signal timing to that assumed in Configuration 1. Figure 15. Intersection Configurations for Traffic Operational Analysis (Continued) 4.1.2 Modeling Approach A total of 349 scenarios were modeled in order to cover a range of vehicle and pedestrian volumes. For each scenario, 30 simulations were run using VISSIM. Thirty runs were completed for each scenario to ensure a large enough sample size to provide a 95 percent confidence level in the results. A total of 10,470 simulation runs were conducted. 4.1.3 Model Calibration and Validation To ensure the results generated in the VISSIM model were accurate and reasonable, two model validation analyses were conducted. The first evaluated the delay parameters for the three configurations described above using the Highway Capacity Manual (32) procedures as implemented in the Highway Capacity Software Release 5 (HCS), and by using the Synchro 7 software program. Volume and delay data were collected at two of the observational field study locations and used in the second validation analysis. In VISSIM, saturation flow rates values cannot be modified directly because they are a function of the car following model, and therefore determined through safety distance parameters. Conversations with PTV America, vendor of VISSIM in North America, indicated 44
VISSIM simulation can result in various saturation flow rates depending on a number of factors. A series of tests were conducted to determine the correct set of safety distance parameters to produce results similar to those produced by HCS and Synchro. Saturation flow rates, right-turn delay, and queue lengths produced in the VISSIM model closely correlated to the results measured in the field. HCS and Synchro Comparison For Configuration 1, HCS and Synchro were used to analyze the right-turn delay for various volume alternatives, and results such as delay, queue length, and saturation flow rates were obtained and used for validation. The HCS analysis and Synchro analysis produced similar saturation flow rates and delay results. Table 9 compares the results of the HCS, Synchro, and VISSIM analyses. Table 9. HCS and Synchro Right-Turn Movement Delay Calibration Results Traffic volume (veh/h) Right-turn volume (veh/h) 50 250 500 HCS Synchro VISSIM HCS Synchro VISSIM HCS Synchro VISSIM 200 14.5 14.2 13.7 25.1 17.2 27.8 800 17.7 16.7 17.4 1600 14.5 14.5 13.7 25.1 25.4 27.8 As shown in Table 9, the VISSIM results were similar to the HCS and Synchro for all cases with the exception of the case when the right-turn volume is 500 veh/h per hour and the conflicting through traffic volume is 200 veh/h. Further review identified that the VISSIM model delay for the right-turning movement increased rapidly around 500 veh/h especially at low conflicting through traffic volumes. However, it was determined that the other measurements at lower right-turning volumes were well calibrated and changing the VISSIM parameters further might reduce the overall accuracy for the range of modeling scenarios. Field Observation Comparison For Configuration 2, two sites were chosen to collect volume and delay data for the calibration. The two sites used for the calibration are located in Portland, Oregon, and Boise, Idaho. The results of the field data and VISSIM model comparison are shown below: ⢠Portland, Oregon: 23rd Street and Burnside Street - Field measurement of right-turn delayâ8.3 sec - VISSIM model estimate of right-turn delayâ8.3 sec ⢠Boise, Idaho: Broadway Avenue and Warm Springs Avenue (skewed intersection) - Field measurement of right-turn delayâ8.3 sec - VISSIM model estimate of right-turn delayâ7.2 sec 45
As shown above, the VISSIM results for right-turn delay matched the field measurements at the intersection in Portland, and were only 0.9 sec (13.3 percent) lower than the field measurements for the site in Boise. Based on the comparison of the VISSIM results to the delays from HCS, Synchro, and field data, it was determined that the VISSIM model was adequately calibrated for use. Base Modeling Results for Each Configuration 4.2 The base modeling results for Configurations 1, 2, and 3 are presented below. 4.2.1 Configuration 1 For Configuration 1, two signal operational scenarios were evaluated. The first scenario assumes the typical right-turn-on-red (RTOR) operation in which a right turn can be made after stopping if there is a sufficient gap in the conflicting through traffic stream and if no pedestrians are present near the crosswalk conflicting with the turning vehicle. The second scenario assumes that RTOR is not allowed and the right-turning vehicle cannot proceed until it receives a green signal indication and the conflicting through traffic is stopped. Figure 16 illustrates the RTOR movement and the pedestrian crossing movement. Figure 16. RTOR and Pedestrian Crossing Movement Considered in Analysis Figure 17 shows the delay for right-turning vehicles for three right-turn volumes for each scenario. As shown in Figure 17, the conflicting through-traffic volume has a substantial impact on the amount of delay for a right-turning vehicle when RTOR is permitted. When conflicting through-traffic volumes approach 1,600 veh/h, and few gaps exist for right-turning vehicles, the delay experienced by vehicles at RTOR intersections approach that of vehicles at intersections where RTOR is not permitted. When RTOR is not permitted, the delay is greater for higher right- turn volumes, but is not impacted by the volume of conflicting through traffic, since the traffic signal green phase is fixed. The greatest benefit of RTOR appears to be achieved when conflicting through traffic volumes are low. 46
Figure 17. Delay Comparison of Configuration 1 - Conventional Right-Turn Lane (With and Without RTOR) 4.2.2 Configuration 2 Figure 18 shows the delay for the right-turn movement for Configuration 2 (channelized right-turn lane with Yield control). As shown in Figure 17, delay increases from approximately 1 to 2 sec/veh for the lower conflicting through volume of 200 veh/h to approximately 10 to 15 sec/veh at a conflicting through volume of 1,600 veh/h. As conflicting through volume increases, the impact of right-turn volume on delay also increases. 4.2.3 Configuration 3 Figure 19 shows the delay for the right-turn movement for Configuration 3 (channelized right-turn lane with a signal-controlled right turn). For this configuration, it was assumed that RTOR was not permitted, although it is recognized that many intersections with signalized channelized right-turn lanes allow RTOR for single-lane right-turn configurations. The reasons for assuming no RTOR is because, in most cases, signalization of the right-turn is typically implemented at locations with high right-turn volumes, high pedestrian crossing volumes, or both. Under these circumstances, RTOR is typically considered problematic due to pedestrian conflicts and not as beneficial to vehicles since a majority of the right-turning vehicles will be served during the green phase of signal. In addition, a primary purpose of evaluating Configuration 3 is to compare the results to Configuration 1 under similar signal operational assumptions to determine the extent of delay change by channelizing the signalized right turn. Right-Turn Hourly Volume 47
Figure 18. Delay for Configuration 2 (Yield-Controlled Channelized Right-Turn Lane) Figure 19. Delay for Configuration 3 (Signalized Channelized Right-Turn Lane) Right-Turn Hourly Volume Right-Turn Hourly Volume 48
As shown in Figure 19, the right-turn delays ranged from approximately 14 sec for a right- turn volume of 100 veh/h to approximately 20 sec for a right-turn volume of 500 veh/h. This is compared to approximately 15 and 29 sec, respectively, for Configuration 1. When comparing the results shown in Figure 19 with those shown in Figure 17 for the âNo RTORâ scenario, there appears to be a much larger difference in delay between the three volume levels for Configuration 1 (conventional right-turn lane) than for Configuration 3 (signalized channelized right-turn lane). Since traffic volumes and traffic control assumptions were identical in both scenarios, this difference does not seem reasonable. Further review found that the delay for right-turn volume increased substantially between 400 and 500 veh/h for Configuration 1 with No RTOR. This delay increase did not occur for Configuration 3. Other programs such as HCS and Synchro model both configurations identically and therefore do not support such a substantial difference. Therefore, caution is recommended with regard to the specific values shown reported for the 500 veh/h right-turn scenarios. 4.2.4 Right-Turn Delay Reduction Due to Channelized Right-Turn Lane for Base Configurations Figure 20 shows the right-turn vehicle delay for each configuration for right-turning volumes of 100 veh/h, 300 veh/h, and 500 veh/h. The No RTOR option for Configuration 1 is not included in Figure 20 because it is typically only used at complex intersections where signal strategies, such as overlap phasing for the right-turns, are utilized. Figure 20. Delay Comparison of Configurations 1, 2, and 3 0 5 10 15 20 25 30 200 400 600 800 1000 1200 1400 1600 D el ay (s ec /v eh ) Config #1 (Signal with RTOR) Config #2 (CRTL Yield Controlled) Config #3 (Signalized CRTL No RTOR) Through Volume (veh/h) C1-100 C1-300 C1-500 C2-100 C2-300 C2-500 C3-100 C3-300 C3-500 Configuration and Right-Turn Hourly Volume 49
The yield-controlled channelized right-turn lane has the lowest delay of the three configurations. At very low right-turn volumes, the impact of a yield-controlled channelized right-turn lane compared with a conventional traffic signal with RTOR is relatively small. This is due to the fact that delays are low in general when right-turn volumes are low. However, the impact of a yield-controlled channelized right-turn lane increases as the conflicting through traffic volume increases. When the conflicting through traffic volume is between 1,200 veh/h and 1,600 veh/h, Configuration 3 (signalized channelized right-turn lane) experiences similar delays to Configuration 1 (signalized conventional right-turn lane with RTOR), which indicates that there are fewer gaps for RTOR vehicles at these conflicting through-traffic volumes. At a conflicting through volume of approximately 1,400 veh/h, the right-turn vehicle delays for Configuration 3 are similar to those in Configuration 2. Figure 21 shows the resulting delay reductions due to the channelized right-turn lane in Configuration 2 versus the conventional right-turn lane with RTOR in Configuration 1. Figure 21. Right-Turn Delay Reduction Due to a Channelized Right-Turn Lane Configuration 1 (RTOR) Vs. Configuration 2 As shown in Figure 21, the average vehicle delay reduction for right-turning vehicles at the yield-controlled channelized right-turn lane increases slightly as the right-turn volume increases. This indicates that the channelized right-turn lane reduces delay compared to a conventional right-turn lane with RTOR, even at high conflicting through traffic volumes. The delay shown in Figure 21 equates to a 25 to 75 percent reduction for right-turning vehicles. Right-Turn Hourly Volume 50
The greater reduction in delay that results from the increase in conflicting through traffic volumes is likely because the RTOR vehicles for Configuration 1 require a larger gap in traffic than the merging vehicles for Configuration 2 during the red signal phase. Figure 22 shows a similar comparison with the Configuration 1 without RTOR option. As shown in Figure 22, the delay reduction due to the channelized right-turn lane decreases as the conflicting through traffic volume increases, even without the RTOR for Configuration 1. Figure 22. Right Turn Delay Reduction Due to a Channelized Right-Turn Lane Configuration 1 (Without RTOR) Versus Configuration 2 4.2.5 Summary of Results for Base Configurations The analysis results of right-turn delay for each base configuration are summarized below: ⢠For Configuration 1 (conventional right-turn lane), conflicting through-traffic volume has a substantial impact on the amount of delay for a right-turning vehicle when RTOR is permitted. When conflicting through-traffic volumes approach 1,600 veh/h, few gaps exist for right-turning vehicles, and the delay experienced by vehicles at RTOR intersections approaches that of vehicles at intersections where RTOR is not permitted. Thus, the greatest benefit of RTOR appears to be achieved when conflicting through traffic volumes are low. ⢠For Configuration 2 (yield-controlled channelized right-turn lane), delay increases from approximately 1 to 2 sec/veh at a conflicting through volume of 200 veh/h to approximately 10 to 15 sec/veh at a conflicting through volume of 1,600 veh/h. As conflicting through volume increases, the impact of right-turn volume on delay also increases. Right-Turn Hourly Volume 51
⢠For Configuration 3 (signalized channelized right-turn lane), delay is generally not impacted by the volume of conflicting traffic on the cross street, unless the signal timing is changed to accommodate conflicting traffic volumes. Therefore, signalization of the channelized right-turn lane provides traffic operational benefits only at high conflicting volumes on the cross street. Delays ranged from approximately 14 to 20 seconds for right-turn volumes of 100 to 500 veh/h, respectively. Based on these findings, the following can be concluded: ⢠The use of a yield-controlled channelized right-turn lane can substantially reduce the delay experienced by right-turning vehicles. Comparing Configuration 2 to Configuration 1 with RTOR, the channelized right-turn lane provides a delay reduction of between 25 and 75 percent for right-turning vehicles, and provides a delay reduction even at high conflicting through traffic volumes. ⢠At lower right-turn volumes, the traffic operational benefit of a channelized right-turn lane is relatively small as compared with the conventional right-turn lane in Configuration 1. ⢠At high conflicting traffic volumes on the cross street, delay experienced by right- turning vehicles becomes similar for yield- and signal-controlled conditions at channelized right-turn lanes. Impacts of Pedestrians on Base Configuration Results 4.3 A key focus of this research was on how pedestrians use the channelized right-turn lane and the effects of pedestrians on the operation of the channelized right-turn lane. In order to evaluate the operational effects of pedestrians, the following issues were evaluated: ⢠The impact of pedestrian crossings on right-turn delay for Configuration 2 (yield condition) ⢠The effect of crosswalk location on the delay to right-turning vehicles for Configuration 2 ⢠Delay to pedestrians waiting to find a gap in right-turning traffic Each of these issues was evaluated using the VISSIM models developed for the base configurations. 4.3.1 Impact of Pedestrian Crossings on Delay at Channelized Right-Turn Lanes Figure 23 shows the impact to right-turning delay of various pedestrian volumes for the three study configurations. The model assumes that all vehicles yield to pedestrians approaching the crosswalk; however, the observational studies discussed in Chapter 3 of this report indicate that drivers often do not yield to pedestrians waiting to cross, but instead only to those who have begun crossing. Therefore, the delay data shown in Figure 23 may be slightly greater than what 52
would be experienced in a location in which a portion of the vehicles do not yield to pedestrians approaching the crosswalk. Figure 23. Delay Due to Pedestrian CrossingsâConfiguration 2 Channelized Right Turn Lane (300 veh/h Right-Turn and 800 veh/h Conflicting Through) As shown in Figure 23, pedestrian volume has a clear effect on the right-turn delay in Configurations 1 and 2. The increase in delay from zero pedestrians to a pedestrian crossing volume of 200 ped/h is about 50 percent for Configuration 1 and 60 percent for Configuration 2. For all pedestrian volumes, the yield-controlled channelized right-turn lane configuration results in lower delay for right-turning vehicles than a conventional right-turn lane, but at the higher pedestrian volumes the delay for right-turning vehicles nearly doubles. The delay for Configuration 1 with RTOR is close to the delay for Configuration 3 (which does not have RTOR) at the highest pedestrian volumes, indicating that pedestrian crossings substantially reduce the ability of vehicles to turn right during the red signal phase (when the pedestrian have the âwalkâ indication at the traffic signal). This supports the notion that if pedestrian crossing volumes are very high, RTOR has marginal benefit. Figure 24 shows the analysis results for Configuration 2 with right-turn volumes of 100, 300, and 500 veh/h. As shown in the figure, all three right-turn volume scenarios are affected similarly by the pedestrian crossings. At right-turn volumes of 500 veh/h, there is an increase in delay of 4.5 sec (70 percent)âfrom 0 to 200 ped/hâand at right-turn volumes of 100 veh/h, the increase in delay from 0 to 200 ped/h is about 2.5 sec (70 percent). 0 2 4 6 8 10 12 14 16 18 20 0 50 100 150 200 R ig ht T ur n D el ay (s ec /v eh ) Pedestrian Volume (ped/h) Config 1 Config 2 Config 3 53
Figure 24. Delay Due to Pedestrian CrossingsâConfiguration 2 Channelized Right-Turn Lane (800 veh/h Conflicting Through Volume) 4.3.2 Impact of Crosswalk Location Three separate crosswalk locations (upstream, center, and downstream) were modeled for Configuration 2. Table 10 shows the results of the crosswalk location on right-turn delay for a location with a right-turn volume of 300 veh/h and a pedestrian volume of 50 ped/h. The results show a marginal difference in average delay. Table 10. Delay Impacts of Crosswalk Location (300 vph and 50 ped/h) Crosswalk location Upstream Middle Downstream Delay (sec) 5.7 6.2 5.9 4.3.3 Potential Delay to Pedestrians Figure 25 shows the potential delay a pedestrian might experience for pedestrian volumes ranging from 50 to 200 ped/h and right-turn volumes of 100 to 500 veh/h and assuming that vehicles do not yield to pedestrians. This scenario represents a âworst case scenarioâ for pedestrians, since observational studies revealed that approximately 40 percent of the vehicles do yield to pedestrians waiting to cross and nearly all yield once a pedestrian enters the crosswalk. As shown in Figure 25, the potential delay for pedestrians is relatively large at right-turn volumes of 300 and 500 veh/h. At such high right-turn volumes, pedestrians may become frustrated while trying to cross a channelized right-turn lane and may run across or accept very small gaps in traffic. 0 2 4 6 8 10 12 14 0 50 100 150 200 R ig ht T ur n D el ay (s ec /v eh ) Pedestrian Volume (ped/h) 100 300 500Right-Turn Hourly Volume 54
Figure 25. Pedestrian Delay Waiting for a Gap in Right-Turning Traffic 4.3.4 Summary of Results for Pedestrian Impacts on Traffic Operations The results of the pedestrian analysis are summarized below: ⢠Pedestrian volume increases right-turn vehicle delay by 50 to 70 percent for Configurations 1 and 2. This is due to a substantially reduced ability of motorists to turn right during a red signal phase. ⢠The location of the crosswalk is not a key factor with respect to delay for right-turn vehicles. ⢠Three separate crosswalk locations (upstream, center, and downstream) were modeled for Configuration 2. Results suggest that crosswalk location has a marginal effect (no more than 0.5 sec) on delay. ⢠At moderate right-turn volumes (300 veh/h), the potential delay to pedestrians waiting for a gap under Configuration 2 is between 15 and 30 seconds, which is likely similar to the level of delay that might be experienced for a signalized crossing. 0 5 10 15 20 25 30 50 100 150 200 R ig ht T ur n D el ay (s ec /v eh ) Pedestrian Volume (ped/h) 100 300 500Right-Turn Hourly Volume 55
Impacts of Geometric Characteristics and Signal Phasing on 4.4 Channelized Right-Turn Lane Delay The geometry of the channelized right-turn lane for Configuration 2 as well as the type of signal phasing for Configuration 3 are thought to affect the delay experienced by right-turning vehicles. The VISSIM simulation models created for the delay studies were used to quantify the relative impact of these factors: ⢠Addition of an acceleration lane (Configuration 2) ⢠Channelized right-turn lane radius (Configuration 2) ⢠Impact of adding additional green time by implementing an overlap phase for a signalized channelized right-turn lane (Configuration 3) 4.4.1 Acceleration Lane Figure 26 shows the simulation results for Configuration 2 with and without a 61-m (200-ft), full-width acceleration lane. The addition of an acceleration lane reduces the delay for the full range of conflicting through volumes and right-turning volumes. The acceleration lane reduces the right-turn delay by 65 percent at low conflicting through volumes and by 85 percent at higher conflicting through volumes. Figure 26. Delay Comparison With Acceleration Lane (Configuration 2) Right-Turn Hourly Volume 56
4.4.2 Channelized Right-Turn Lane Radius and Speed Impacts The effect of channelized right-turn lane radius on right-turn delay was evaluated by changing the speed of the channelized right-turn lane for various conflicting through volumes and for two roadway speeds. Vehicle speed along the channelized right-turn lane was used as a surrogate for channelized right-turn lane radius, since vehicle speed is limited on narrower curves (smaller radius channelized right-turn lanes) and higher for channelized right-turn lanes with larger radii. Table 11 shows the results of the analysis for Configuration 2. Table 11. Delay Impacts of Channelized Right-Turn Lane Speed/Radius for Configuration 2 Two through lanes traffic volume (veh/h) Delay for right-turning vehicles 10 mi/h (15- to 20-ft radius) 15 mi/h (40- to 60-ft radius) 20 mi/h (90- to 110-ft radius) Conflicting through volume speed = 35 mi/h 600 4.3 3.4 2.9 1,000 8.4 7.1 6.5 1,400 13.3 11.5 10.8 Conflicting through volume speed = 45 mi/h 600 4.5 3.6 3.1 1,000 8.0 6.8 6.1 1,000 12.6 11.0 10.3 As shown in Table 11, increasing the radius of the right turn (which increases the travel speed along the channelized right-turn lane) reduces the delay by approximately 10 to 20 percent for each 8-km/h (5-mi/h) increase in turning speed. Larger delay reductions are seen at lower through-lane volumes. Delay decreases slightly when the speed of the conflicting through volume is increased from 56 to 72 km/h (35 to 45 mi/h) for through volumes of 1,000 veh/h or greater, but increases slightly for the lower volumes. Based on the observational studies, most of the medium island sizes had a radius of 18 to 31 m (60 to 100 ft). 4.4.3 Traffic Signal Phasing for Signalized Channelized Right-Turn Lanes At a signalized channelized right-turn lane (Configuration 3), it is common for traffic engineers to provide extra green time to the right-turn movement without increasing cycle length by overlapping the right turn with the cross street left turn. Figure 27 illustrates the concept of a right-turn overlap. A potential drawback of the right-turn overlap phasing is that U-turns cannot be permitted from the cross-street left-turn lane, as they may conflict with right-turning vehicles. The elimination of the U-turn can be a significant issue in states where U-turns are allowed at all intersections and in areas that have median access control and U-turns are the primary means of providing left-turn access to businesses. 57
Figure 27. Right-Turn Overlap Table 12 compares the delay for the base condition to providing additional green time through use of an overlap signal phase. An analysis was conducted for provision of 10, 15, and 20 seconds of additional green time to the 45-sec signal phase under the base condition for the right-turn movement. Table 12. Delay Impacts of Adding Additional Green Time to Right-Turn Movement Overlap/added green time for right turn (sec) Average right-turn delay (sec) (for pedestrian volume of 100 ped/h) Right-turn volume (veh/h) 100 300 500 0 6.2 10.7 19.9 10 5.9 9.5 16.0 15 5.8 9.0 14.8 20 5.5 8.5 13.5 As shown in Table 12, the additional green time is more effective at reducing delay as the right-turn volume increases from 100 to 500 veh/h. Each increment of addition green time for the right turn movement provides approximately a 5 to 10 percent decrease in delay for the right-turn vehicles. 58
4.4.4 Summary of Results for Geometric and Signal Element on Channelized Right-Turn Lane Traffic Operations The results of the geometric and signal operations analysis of right-turn delay suggest the following: ⢠Acceleration lanes substantially reduce right-turn delay at all volume levels. ⢠Increasing the radius of the channelized right-turn roadway reduced the delay by approximately 10 to 20 percent for each 8 km/h (5-mi/h) increase in turning speed. Larger delay reductions were observed at lower through-lane volumes. ⢠Use of an overlap phase or other methods of providing additional green time to right- turning vehicles can substantially reduce the delay for a signalized channelized right-turn lane but may result in other impacts to intersection operations such as restricting U-turns maneuvers. Summary of Traffic Operational Analysis Findings 4.5 Based on the results of the simulation modeling, channelized right-turn lanes can substantially reduce delay for right-turning vehicles in nearly every traffic volume scenario. Site- specific factors, such as pedestrian volumes and the geometry of the channelized right-turn lane, have an effect on the level of improvement. Therefore, these factors are important in determining the delay benefits that may result from installation of the channelized right-turn lane. Following are the key findings: ⢠A yield-controlled channelized right-turn lane can decrease right-turn delay by 25 to 75 percent compared with a conventional right-turn lane at a signalized intersection. At most volume levels, a conventional right-turn lane at a signalized intersection provides lower delay than a signalized channelized right-turn lane due to the use of RTOR. At high pedestrian volumes or high conflicting cross-street traffic volumes, a conventional right-turn lane with RTOR results in similar delays to signal control without RTOR. Thus, the greatest traffic operational benefit of a conventional right-turn lane with RTOR appears to be achieved when conflicting traffic volumes on the cross street are low to moderate. ⢠A pedestrian volume of approximately 200 ped/h increases right-turn delay by approximately 60 percent on a yield-controlled channelized right-turn lane compared to a base condition of no pedestrians, assuming vehicles yield to pedestrians. However, for all pedestrian volumes, the channelized right-turn lane results in lower delay for right- turning vehicles than a conventional right-turn lane. ⢠When right-turn volumes are greater than 300 veh/h, the potential delay for pedestrians waiting for a gap to cross a channelized right-turn lane could be between 15 and 30 seconds. ⢠The addition of an acceleration lane reduces the right-turn delay by 65 to 85 percent depending on the conflicting through traffic volume. 59
⢠Increasing the radius of the yield-controlled channelized right-turn lane from approximately 5 to 6 m (15 to 20 ft) up to 24 to 31 m (80 to 100 ft) results in a decrease in right-turn delay of approximately 20 to 50 percent. ⢠Three separate crosswalk locations (upstream, center, and downstream) were modeled for Configuration 2. Results suggest that crosswalk location has a marginal effect (no more than 0.5 sec) on delay. ⢠Use of an overlap phase, or other methods of providing additional green time to right- turning vehicles, can substantially reduce the delay for a signalized channelized right- turn lane, but may result in other impacts to intersection operations, such as restricting U-turn maneuvers. 60
