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62 CHAPTER 6 Study Extensions The objective of this chapter is to extend the analysis results able for every participant. The section on simulation models from Chapter 5 to a broader and more applied context. Because does describe an approach for using simulation to extract sur- of limited resources, only a small number of sites were repre- rogate safety measures and a way to model the unique aspects sented in the field experiment. But clearly, the crossing chal- of how blind pedestrians interact with vehicles. However, the lenges for pedestrians who are blind extend to other geometries best measure of safety remains the field-measured rate of O&M and traffic patterns. This chapter attempts to provide this interventions presented in Chapter 5. Chapter 7 discusses in type of extension in two ways: more detail the interpretation of the results and the implica- tions for roundabout and CTL facility design. 1. The development of pedestrian delay models that allow the analyst to predict the expected pedestrian delay at a cross- ing location based on traffic patterns and behavioral attri- Delay Estimation butes of drivers and pedestrians. Introduction 2. A discussion on how to apply traffic simulation models to extrapolate the effects of other treatments to other sites, The analysis results in Chapter 5 confirmed the hypothesis including treatment combinations not captured in the that pedestrian­vehicle interaction at unsignalized round- experimental field trials. about and channelized turn lane crosswalks is characterized by a mix of pedestrians' (crossable) gap acceptance and driver This chapter presents the pedestrian delay models and dis- yielding behavior. Both represent crossing opportunities since cussion of traffic simulation models consecutively. The reader pedestrians cross in between two vehicles (gap) or in front of should be aware that with limited field data, both areas of a yielding vehicle. The crosswalks are typically marked with a extension are to be treated with care. The analyst should always zebra pattern or another form of marking (Rodegerdts et al. apply expert judgment in any treatment installation and eval- 2007) and feature a pedestrian splitter island to separate the uation. Other national resources provide additional informa- interaction between different directions of moving traffic. tion on the effectiveness of different treatments (Fitzpatrick State motor vehicle codes commonly give pedestrians the right- et al. 2006) and on case studies describing lessons learned from of-way within the crosswalk, suggesting that roundabouts and their installation (Zegeer et al. 2002). The approach for devel- CTLs should be very accessible to pedestrians. But yielding oping pedestrian delay models has been separately published laws can be misinterpreted, and the actual yielding behavior in Schroeder and Rouphail (2010). varies over a range of observed values at different sites and The principal focus of the two extensions is on pedestrian geometries (Fitzpatrick et al. 2006). Consequently, pedestrians delay, not risk. This is a clear limitation that needs to be rec- are expected to experience some delay when attempting to ognized early on. The NCHRP Project 3-78A team attempted cross at these locations. to follow similar approaches to predict the safety perfor- The interaction of the two modes therefore needs to be rep- mance of a pedestrian crossing using regression and simulation resented by a "mixed-priority delay model" (Schroeder and techniques. The regression-based attempt was not successful Rouphail 2010) that acknowledges the mix of yielding and gap due to the rare occurrence of O&M interventions. In order to acceptance. The 2000 Highway Capacity Manual (TRB 2000), develop a risk prediction model from field data, a different the guidebook for traffic operational analysis methodologies dependent variable would be needed that is readily observ- for the United States and many other countries, currently offers