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91 The selected safety measure of O&M interventions had The team attempted to develop a secondary measure of been used in several prior studies involving crossings of blind pedestrian safety by using expert ratings of video clips recorded pedestrians. The measure is related to the concept of traffic during the trials. The approach aimed to extract potentially conflicts, which is an increasingly common safety perfor- risky video clips that included, but were not limited to, all inter- mance measure. A traffic conflict is typically defined as an ventions recorded at a site. These short video clips were then interaction between two vehicles (or a vehicle and a pedes- shown in randomized order to a panel of expert reviewers, who trian) for which a collision is imminent pending an evasive rated pedestrian safety in the clip on a scale of 1 to 5. This action by any of the involved parties. The categorization for approach was tested for the pretest condition at the CTL, but what constitutes a risky time-to-collision is typically defined did not result in a reliable alternative to the intervention by a 2-s threshold. measure. The exercise did establish that there is agreement The approach of using O&M interventions as a surrogate within most of the reviewers that events that resulted in O&M safety measure uses a similar underlying principle. The O&M interventions were in fact risky. It further established that specialist intervenes when he or she feels that the crossing deci- most of the control clips that were added to the sample to sion by the pedestrian would result in undue risk. For many of establish a baseline for safe behavior resulted in mostly low- the interventions, it is likely that an actual collision could have risk ratings. However, the exercise proved inconclusive as far been avoided if the driver had performed an emergency brak- as any borderline risky events are concerned. ing maneuver. However, this level of risk was deemed un- Overall, the activity gave the team confidence in the via- acceptable to the pedestrian as well as to the approaching bility of the O&M intervention measure for pedestrian risk driver and any following vehicles. but did not result in any further information about safety Clearly, the intervention measure is subject to variability performance. Due to project constraints, this approach was among different O&M specialists. It is human nature to have not applied to the remaining test sites. The team does believe, however, that there is merit in continuing research in this different perceptions of risk, and consequently it is expected area. In particular, it would be beneficial to develop an objec- that the threshold for an intervention may differ somewhat tive performance of safety that is based on the field-measured between two O&M experts. In this research, the team attempted time-to-collision based on vehicle trajectories (rather than on to minimize this variability by having the same O&M specialist expert judgment). The results of the safety rating exercise are perform all the experimental trials. presented in Appendix H to be a resource for further research The O&M intervention is further a coarse measure in that activities. it stratifies pedestrian risk on a binary (yes/no) scale. In real- ity, the O&M interventions included a range of situations that represent varying degrees of risk that are difficult to define. Driver Yielding and Enforcement For example, an intervention may include a multiple-threat The treatments tested as part of NCHRP Project 3-78A all situation at a two-lane approach where a pedestrian utilizes a represented infrastructure-based treatments, which was a near-lane yield by a heavy vehicle that masks visual and audi- principal requirement of the project objectives and in keeping tory information about a fast-moving vehicle in the far lane. with Access Board guidelines. The analysis therefore did not On the other hand, an intervention may have occurred if the include any treatments that would be carried by the pedestrian driver of a previously stopped vehicle accelerated at the same in the form of wayfinding or traffic detection technology. The time that the pedestrian stepped out to utilize the yield. These scope further did not include any policy-based treatments such events occurred in particular at the CTL, where traffic queues as increased law enforcement of yielding laws. Nonetheless, frequently spilled back across the crosswalk from the down- the results do seem to suggest that vehicle yields represent valid stream merge point. crossing opportunities that may be utilized by pedestrians The intervention measure does not give a comprehensive who are blind, although at utilization rates less than 100%. safety assessment of the crossing attempts. Similar to collisions, Infrastructure treatments that resulted in increased yielding interventions and conflicts are rare events that depend on a suf- behavior and reduced vehicle speeds were shown to improve ficiently large sample size. The fact that all of the sites exhibited accessibility. some level of interventions (despite the relatively low sample The motor vehicle codes in most U.S. states require driv- size) speaks to their risk to the blind travelers. While no sighted ers to yield to pedestrians in the crosswalk and in some cases pedestrians were involved in these experiments, it is hypothe- even to pedestrians waiting at the crosswalk. However, field- sized that a sighted participant would have been very unlikely observed yielding rates vary widely and are inconsistent across to experience an O&M intervention rate at, for example, 16 locations even with the same crossing treatment installed crossing attempts at a single-lane roundabout, which is sup- (Fitzpatrick et al. 2006). Most states offer additional protection ported by research comparing blind and sighted pedestrians at to blind travelers to what is commonly referred to as "white roundabouts (NIH 2010). cane laws." These are intended to promote driver awareness,