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OCR for page 108
108 Exhibit 10. O&M intervention statistics While the effect of the treatments on the reduction of inter- for CTL crosswalks. ventions is significant, crossing risk still remains. Ashmead et al. (2005) posited that the probability of a dangerous Intervention Rate crossing decision is given by 1­(1­pper crossing)n, where pper crossing is Pre Avg. Min. Max. Std. Dev. the observed intervention rate and n the number of crossing SS-ONLY (n = 16) 9.4% 0.0% 30.0% 9.5% attempts. After 40 crossings (twice per day, 5 days a week, SS+FB (n = 16) 5.6% 0.0% 15.0% 5.2% over 4 weeks), the probabilities of a risky decision at the rates Post of 1.4% and 2.9% are 43.1% and 69.2%, respectively. After SS-ONLY (n = 14) 2.9% 0.0% 15.0% 4.7% 100 crossings, the post intervention rate of 2.9% at the SS-ONLY SS+FB (n = 14) 1.4% 0.0% 10.0% 3.1% crosswalk results in a 94.7% likelihood of a risky decision. Exhibit 11 explores the hypothesis that the intervention rate was related to the time of day that the subjects participated in the study. Members of the research team anecdotally found crosswalk in the pre condition, which corresponds to 9.4% the p.m. periods at the SS-ONLY corner very difficult to cross of crossing attempts. At the SS+FB crosswalk in the pre con- due to high afternoon turning volumes in the channelized dition, the average rate of interventions was 0.9 interventions turn lane. The exhibit further provides insight in the variability per participant, which equates to 5.6% of crossing attempts, as of interventions across participants. Note that participants shown in Exhibit 10. These rates are much higher than for other 5 and 14 did not participate into the post study. Their post observed sites and indicate a lot of risk at this crossing. While intervention rates are shown in the negative to distinguish them some pedestrians didn't experience any interventions, others from participants with zero interventions. Given the inter- had up to six interventions out of 20 crossings at the SS-ONLY vention patterns, the hypothesis that the higher volume resulted crosswalk, resulting in an intervention rate of 30%. While fewer in a greater degree of risk could not be supported. The figures average interventions were observed at the SS+FB crosswalk further illustrate that the degree of risk varies across partici- compared to SS-ONLY, the difference is not statistically pants, even after controlling for time of day. significant (p = 0.1614). The installation of treatments reduced interventions sig- Channelized Turn Lane nificantly at both crosswalks to 2.9% and 1.4% at the SS-ONLY Results Summary and SS+FB corners, respectively (p = 0.0204 and p = 0.0112). This suggests that while the treatments didn't have a huge effect The field evaluation at the channelized turn lane in Charlotte on crossing performance in terms of opportunity utilization showed that participants experienced a lot of delay and risk and mixed results on delay, the impact on interventions seems at this site. Despite the fact that only a single lane needed to clear and noteworthy for both crosswalks. be crossed, the combination of background noise at the busy Exhibit 11. Intervention statistics by subject and time of day. a) SS-ONLY 35.0% PRE 30.0% POST 25.0% Intervention Rate 20.0% 15.0% 10.0% 5.0% 0.0% 6 12 16 1 3 5 8 11 15 2 4 7 9 10 13 14 -5.0% 1:30pm 10:30am 3:30pm 8:30am Subject

OCR for page 108
109 Exhibit 11. (Continued). b) SS+FB 35.0% 30.0% PRE 25.0% POST Intervention Rate 20.0% 15.0% 10.0% 5.0% 0.0% 6 6 12 16 12 16 1 1 3 3 5 5 8 8 11 15 11 15 2 2 4 4 7 7 9 10 13 9 10 13 14 14 -5.0% 1:30pm 10:30am 3:30pm 8:30am Subject intersection and fast approach speeds in the turn lane caused Exhibit 12. Crossing performance summary higher delays and more frequent interventions than at the pre and post at channelized turn lane. roundabout sites, including the two-lane roundabout in SS-ONLY Turn Lane SS+FB Turn Lane Golden. Exhibit 12 summarizes the crossing performance for Performance Measure Pre Post Pre Post the CTL location. Yield Availability 18.4% 18.6% 15.2% 22.0% The installation of the sound strip and lane delineator Gap Availability 34.9% 41.2% 44.7% 49.2% treatments at the SS-ONLY corner did not have a large impact Yield Utilization 50.8% 40.5% 53.1% 64.6% on most of the availability and utilization performance meas- Gap Utilization 60.3% 68.2% 63.2% 89.3% ures when aggregated for all participants. However, individ- 85th percentile Delay (s) 40.9 32.7 38.6 17.9 ual participants seemed to benefit from the treatments, and O&M Interventions 9.4% 5.6% 2.9% 1.4% the treatments further resulted in a significant reduction in interventions.