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40 analysis, these two variables are preferred and are used instead Since this high number of event classifications becomes of P(Yield) and P(CG). The common denominator is further unmanageable, the results in the main portion of the report critical in the extension work described in Chapter 6. combine all near-lane events in three categories (yield, cross- The rates of yield and crossable gap utilization are calcu- able gap, and non-crossable gap) and do the same for far- lated at P(GO|Y) = 0.0% and P(GO|CG) = 33.3%, respectively. lane events, thus simplifying the distinction between a single Delay is defined as the temporal duration from the time the event or multiple events in the far lane substantially. With trial starts until the pedestrian initiates the crossing. The min- this aggregation, the number of nearfar lane event combi- imum delay is less, calculated as the time spent waiting until nations is reduced to nine (Figure 16). The results for the full the first crossing opportunity, which in this case is the yield by event matrix are discussed in detail in Appendix A. vehicle 2. Consequently, the Delay>Min is defined as the dif- The nine event outcomes in Figure 16 can further be put into ference between delay and minimum delay. three categories that are themselves represented as probabilities: PA_Dual: The likelihood of encountering a crossing oppor- Adapting the Framework tunity in both lanes, including yieldyield, yieldCG, CG to Two-Lane Crossings yield, and CGCG events, divided by the total of all events. PA_Half: The likelihood of encountering a crossing oppor- The above framework was initially developed for single- lane approaches. For any crossing situation where the pedes- tunity in only one lane, including yieldnon-CG, CGnon- trian only faces one conflicting lane, crossing opportunities CG, non-CGYield, and non-CGCG events, divided by the total of all events. are uniquely defined by the vehicle state in that lane (yield, PA_None: The likelihood of encountering a crossing oppor- crossable gap, or non-crossable gap). However, at a two-lane tunity in neither lane, including non-CGnon-CG events, crossing, the analysis needs to consider the vehicle state in divided by the total of all events both lanes. The analysis of two-lane crossings therefore distin- guishes between driver behavior in the near lane (the closest This stratification becomes important in light of identifying lane relative to the position of the pedestrian) and the far crossing opportunities and interpreting pedestrian utilization lane. Depending on the crossing location (entry/exit and curb/ of these opportunities. Clearly, a crossing opportunity in both island), the near lane can be the inside or outside lane of the lanes corresponds to a valid crossing strategy. Similarly, if two-lane approach. neither lane exhibits a crossing opportunity, the event clearly The analysis defines the vehicle state in the near lane in the is non-crossable. If only one of the lanes exhibits a crossing same five event categories defined previously: rolling yield opportunity, a conservative pedestrian would be expected (RY), stopped yield (STY), forced yield (FY), crossable gap to wait. A more assertive pedestrian may seize the crosswalk (CG), and non-crossable gap (non-CG). The vehicle state in in hope of eliciting a driver response in, for example, the far the far lane will then be defined relative to the near-lane con- lane. The utilization parameters associated with PA_Dual, dition in the same five principal categories (RY, STY, FY, CG, PA_Half, and PA_None are denoted as PU_Dual, PU_Half, and non-CG). Initially, this results in 25 possible combina- and PU_None, respectively. Definitions of the utilization mea- tions of the near/far-lane vehicle state. sures are consistent with the single-lane analysis framework. Further, the near-lane events typically have some temporal For the purpose of this analysis, it is assumed that only dimension. For example, a crossable gap lasts a certain amount events with a crossing opportunity (either a yield or crossable of time. Similarly, a yield has some duration associated with gap) in both lanes represent valid overall crossing opportunities. it that is related to driver patience and the responsiveness of Consequently, only those events will be included in the dis- the pedestrian. To adequately recognize this temporal dimen- cussion of rates of encounter of crossing opportunities and sion, a separate far-side category is introduced: multiple events. their utilization. The definitions for delay and safety perfor- This category indicates that more than one event took place mance measures are the same as for single-lane crossings. in the far lane during one near-lane event. For example, sev- eral cars could have passed the plane of the crosswalk in the far lane during one large gap in the near lane. For purpose of Research Hypotheses analysis, it is assumed that the last event in the multiple-event The analysis framework hypothesizes that the perform- sequence governs the interaction. In total, the two-lane round- ance measures above describe the most pertinent aspects about analysis thus considers five near-lane event categories of pedestrianvehicle interaction at the test sites. The mea- and 10 far-lane categories (five single-event and five multiple- sures will be used in this research to quantify the operational event categories) for a theoretical 50 possible event combina- differences between test sites and to contrast various cross- tions (see Figure 15). ings at the same site (for example, entry versus exit leg). More

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41 This figure shows a diagram of all possible pedestrianvehicle interaction events at a two-lane crossing. The figure shows five possible event states for the lane nearest the pedestrian: rolling yield, stopped yield, forced yield, crossable gap, and non-crossable gap. Each of these five event states can be associated with the same five event outcomes in the far lane. The far lane can further feature multiple event outcomes, which in turn are classified by the five categories. In total, the figure shows 50 possible event combinations. Figure 15. Full matrix of near-lane and far-lane event combinations. importantly, it is hypothesized that the performance measures are sensitive to the installation of pedestrian crossing treatments (Schroeder and Rouphail 2007). Each treatment is intended to improve one or more of the performance measures. In particular, a treatment that is primarily geared toward improving driver awareness of the crosswalk and the presence of the pedestrian is expected to increase the likelihood of encountering a yield, P(Y_ENC). Yielding behavior is likely also affected by the speed of the vehicle (Geruschat and Hassan 2005), and consequently any traffic calming treatment is likely to increase yielding behavior. The rate of yielding or stop- ping for pedestrians is expected to increase to very high levels for any treatment that shows a solid red indication to drivers This figure shows a diagram of the condensed matrix of pedestrianvehicle interaction events at a two-lane crossing. (Fitzpatrick et al. 2006), which includes the PHB or HAWK The figure shows three possible event states for the lane signal. nearest to the pedestrian: yield, crossable gap, and non-crossable gap. Each of these three event states The availability of crossable gaps is primarily a function of can be associated with the same three event outcomes traffic volume, where higher volumes will decrease the availabil- in the far lane for a total of nine event combinations. ity of crossable gaps. Any upstream metering of traffic through, Figure 16. Condensed matrix of near-lane for example, a signal will also increase the availability of cross- and far-lane event combinations. able gaps as it bunches traffic in platoons. The downside of

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42 vehicle platooning is that it has been linked to a lower Raised crosswalk: Increase P(Yield) and P(GO|Y), and propensity to yield (Schroeder 2008). Pedestrian hybrid beacon: Increase P(Yield) and P(GO|Y). The ability or willingness to utilize yields, P(GO|Y), may be improved by lower ambient sound levels or an amplification Further, the occurrence of crossable gaps, P(CG), is likely of the noise of the approaching vehicle. The sound-strip treat- to vary across sites and study participants depending on traf- ment attempts to do the latter in that it auditorily distinguishes fic volumes and the time of day of the study. Ultimately, the the conflicting traffic stream from the general background traf- four probability terms are hypothesized to affect the delay fic (Inman et al. 2005). The willingness to utilize a yield may experienced by the pedestrians. An increase in one or more further be affected by any treatment that gives the pedestrian of the probability terms is expected to decrease the experi- confirmation in the form of an audible message (APS device or enced delay as more crossing opportunities are available and/ other audible information device) or that slows traffic down to or utilized. make the pedestrian more comfortable interacting with traffic. The hypothesized impact on pedestrian safety is more dif- The ability or willingness to utilize crossable gaps, ficult to define. For example, one would generally expect that P(GO|CG), is also expected to be correlated with the rela- a PHB would create more frequent and safe crossing opportu- tive noise of conflicting traffic to the overall level of ambi- nities. However, experience at pedestrian signals (Fitzpatrick ent noise. Again, the sound-strip treatment is hypothesized et al. 2006) shows that driver compliance may be less than to help in this regard in that the absence of sound cues cor- 100%. Consequently, reliance on the audible device message responds to a potentially crossable gap. An upstream signal from the signal may contribute to additional risk. In this study, that meters overall traffic on the approach may generate "all- participants were generally instructed to not solely rely on the quiet" periods during which a blind pedestrian can more APS message but to always use their own judgment and audi- reliably identify a crossable gap. ble perception of the traffic environment. In principle, the For the treatments tested, the following hypotheses are made: research hypothesizes that any of the treatments will con- tribute to reducing pedestrian delay and enhancing safety. Flashing beacon: Increase P(Yield) and P(GO|Y), However, it is recognized that the safety performance evalua- Sound strips: Increase P(GO|Y) and P(GO|CG), tion may deliver mixed results.