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59 platoons, while still showing beneficial impacts on pedestrian (PS-RAL) was performed as part of an earlier research project crossing performance as discussed above. (NIH 2010). The remaining data collection occurred under At the exit leg, the average pretest speed of 17.7 mph was the auspices of NCHRP Project 3-78A. For these 11 rounds of reduced to 16.1 mph (p < 0.0001). While statistically signifi- testing, the same O&M specialist was used to establish con- cant, the practical implication of this speed reduction is mar- sistency and uniformity in the experimental design. This point ginal in terms of vehicle delay. But again, as the analysis above is especially important in light of the rate of O&M interven- showed, the RCW had a very positive impact on pedestrian tions, an important safety measure used in the analysis. crossing performance, despite the relatively low speed impact. The analysis framework was discussed in detail in Chapter 4 and uses a four-pronged approach for assessing the accessibil- ity of a crossing through (1) the availability of crossing oppor- Pedestrian Hybrid Beacon tunities, (2) the rate of utilization of these opportunities, (3) the A special queuing study was performed at the PHB installa- delay experienced by the pedestrian, and (4) the level of risk tion to address concerns that the signal would cause extensive associated with the crossing. The first two measures are largely queuing and that those queues could spill back into the circu- intended to find an explanation for the latter two. This section lating lane. The analysis measured the maximum queue length summarizes some of the delay and risk measures to allow a for each pedestrian crossing in all pretest and posttest trials. The comparison across the different test locations. maximum queue was defined as the longest pedestrian-induced Figure 23 summarizes the average delay across all partic- ipants for the 12 locations. The graph further contains error queue length measured in vehicles. Queues were measured rel- bars at 1 standard error of the estimate of the mean. The stan- ative to the crosswalk and therefore do not include additional dard error is calculated by dividing the standard deviation of vehicles that were waiting to enter the roundabout downstream the estimate by the square root of the sample size (number of the crosswalk (at the entry). Vehicle queues were combined of participants). The summary chart shows highest delays for both lanes since no significant difference was observed observed at the two CTL locations in the pretest treatment con- between queues in the inside and outside lanes. dition as well as for the DAV-CLT single-lane roundabout. The results showed that the average maximum queue length Interestingly, these three data points represent very differ- increased from 2.3 to 5.0 vehicles at the entry and from 1.5 to ent traffic conditions, but were all located in Charlotte. At 3.9 vehicles at the exit over both approach lanes. The increases DAV-CLT, volumes were low and participants were delayed in average maximum queues are significant at p < 0.0001. With despite ample gap crossing opportunities as many waited for available queue storage of two vehicles (one per lane) at the exit all-quiet periods. At the two CTL crossings, traffic volumes leg, it is evident that the maximum queue sometimes spilled were much higher, and the delay was exacerbated by a very back into the circulating lane. With the installation of the PHB, high level of ambient noise from the main intersection. All that proportion of maximum queues greater than two vehicles three of these locations were characterized by a low propensity increased from 29.8% to 69.2%. However, the average queue of drivers to yield, which may be characteristic of the local driv- is expected to be much lower, so that the overall effect of the ing culture or may be coincidence. With treatment installation, PHB installation on vehicle queues is considered to be mar- the average delay at CTL crossings was reduced. No treatment ginal. In fact, a determined yielder may be stopped for 10 or was tested at the single-lane roundabout. more seconds waiting for the pedestrian to cross and is likely Of the remaining sites, the two-lane roundabout crossings to cause similar if not more delay to a driver waiting at the exhibited the highest average delay and the highest variabil- PHB, as evident by some long queues observed in the pretest. ity across participants. The two-lane roundabout delay was More detail on the queuing analysis is given in Appendix A. reduced significantly with installation of either crossing treat- ment (RCW and PHB) to levels that were below the remaining single-lane roundabout delays. It is important to emphasize Summary of Results that the studies at the two-lane and single-lane roundabouts in This chapter presented findings from 12 rounds of field Golden were performed concurrently with the same partici- studies performed at a total of seven pedestrian crossings: two pants. Consequently, these sites can be directly compared. The channelized right turn lanes, three single-lane roundabout comparison shows that delays were higher at the two-lane crossings, and two two-lane roundabout crossings. While no roundabout and there was greater variability across partici- treatments were tested at the single-lane roundabout loca- pants. The assessment of the PHB and RCW treatments fur- tions, the remaining crossings and studies included pretest ther highlights that pedestrian delay and risk were effectively and posttest comparisons of the effectiveness of different improved over the base condition of the single-lane round- treatments in improving accessibility of these locations. All about comparison site. 12 studies were performed using the same experimental Figure 24 shows the comparative results of O&M interven- protocol. The study for one of the single-lane roundabouts tions across the 12 test conditions. Again the figure shows the
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Average Delay (s) 35 26.2 25.3 30 23.4 25 18.5 17.0 16.0 20 12.1 15 12.2 11.1 11.9 10 8.0 5.8 5 0 PS-RAL* DAV-CLT PHB PRE GOL-PRE RCW PRE PHB POST GOL-POST SS+FB PRE RCW POST SS+FB POST SS-ONLY PRE SS-ONLY POST Channelized Turn Single-Lane RBT Two-Lane RBT Lane This figure shows a bar chart of the summary of the delay results at all test sites and all study conditions. The graph shows the average pedestrian delay observed for each of 12 studies as well as the standard error of that estimate. The results are discussed in the text. Error bars shown at 1 standard error *Data collection performed in prior research Figure 23. Summary of 85th percentile delay for all sites. O&M Interventions 14% 9.4% 12% 10% 8% 5.6% 6% 3.9% 2.9% 2.8% 4% 2.4% 1.4% 0.8% 1.4% 2% 0.5% 0.0% 0.0% 0% SS-ONLY PRE SS+FB PRE DAV-CLT PS-RAL* GOL-PRE PHB PRE RCW PRE SS+FB POST GOL-POST PHB POST RCW POST SS-ONLY POST Channelized Turn Single-Lane RBT Two-Lane RBT Lane This figure shows a bar chart of the summary of the O&M intervention results at all test sites and all study conditions. The graph shows the average pedestrian delay observed for each of 12 studies as well as the standard error of that estimate. The results are discussed in the text. Error bars shown at one standard error *Data collection performed in prior research Figure 24. Summary of O&M interventions for all sites.
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61 average observed over all participants and the standard error Project 3-78A. With the use of different O&M instructors there of the estimate. is the potential that individual differences may be a contribut- The intervention comparison shows very high risk at the ing factor to the difference in intervention rates. Since the CTL crossings in the pretest condition along with a very high remaining 11 data points all involved the same O&M specialist, variability across participants. Intervention rates at the CTL greater comfort exists that the results are comparable. Conse- locations were reduced with treatment installation, but some quently, the two-lane roundabout pretest conditions exhibited interventions remained even in the posttest condition. For the the greatest level of risk among the roundabouts and the largest roundabouts, the highest intervention rate was observed at PS- variability across participants. With treatment installation, no RAL, although this study was not performed as part of NCHRP interventions were observed at these locations.