Unlike other types of controlled intersections, drivers do not always comply with the “yield to pedestrian” sign at the roundabouts. This paper aims to identify the contributing factors affecting the likelihood of driver yielding to pedestrians at two-lane roundabouts. It further models the likelihood of driver yielding based on these factors using logistic regression. The models have been applied to 1150 controlled pedestrian crossings at entry and exit legs of two-lane approaches of six roundabouts across the country. The logistic regression models developed support prior research that the likelihood of driver yielding at the entry leg of roundabouts is higher than at the exit. Drivers tend to yield to pedestrians carrying a white cane more often than to sighted pedestrians. Drivers traveling in the far lane, relative to pedestrian location, have a lower probability of yielding to a pedestrian. As the speed increases the probability of driver yielding decreases. At the exit leg of the roundabout, drivers turning right from the adjacent lane have a lower propensity of yielding than drivers coming from other directions. The findings of this paper further suggest that although there has been much debate on pedestrian right-of-way laws and distinction between pedestrian waiting positions (in the street versus at the curb), this factor does not have a significant impact on driver yielding rate. The logistic regression models also quantify the effect of each of these factors on propensity of driver yielding. The models include variables which are specific to each study location and explain the impact size of each study location on probability of yielding. The models generated in this research will be useful to transportation professionals and researchers interested in understanding the factors that impact driver yielding at modern roundabouts. The results of the research can be used to isolate factors that may increase yielding (such as lower roundabout approach speeds), and can feasibly be incorporated into microsimulation algorithms to model driver yielding at roundabouts.
This paper develops and implements the Conflict-based Assessment of Pedestrian Safety (CAPS) methodology for evaluating pedestrian accessibility at complex intersections. In past years, a significant research has been done on pedestrian access to modern roundabouts and other complex intersection forms, including a significant focus on the accessibility for pedestrians who are blind. A majority of these studies have relied on actual street crossings by study participants under supervision of trained Orientation and Mobility (O&M) Specialist. These crossing studies were used to evaluate risk from a measurement of intervention events, where the O&M specialist had to physically stop the participant from crossing. While providing arguably the most accurate data for the crossing risk at a particular intersection, actual street crossings can be dangerous to the study participants, and are further very time consuming and expensive to conduct. The CAPS method presented in this paper emphasizes the use of conflict-based safety factors to quantify risk. The CAPS method relates pedestrian crossing decisions to advanced measurements of vehicle dynamics to estimate lane-by-lane conflicts. CAPS identifies the grade of conflict based on a score generated on a five-criterion rating scale. Each of these criteria or factors has different severity levels, and when combined, provides an overall risk rating of the crossing decision. The CAPS framework was applied to a study of blind pedestrian crossings at a multi-lane roundabout. The resulting risk scores were calibrated from actual O&M interventions observed during the study to give confidence in the CAPS performance. The calibrated CAPS framework correctly matched all (high risk) O&M intervention events, and further identifies other (lower risk) pedestrian-vehicle conflicts. The resulting method has the potential to allow for a faster and most importantly safer evaluation of complex intersections for pedestrian access. Since all factors are measured prior to the pedestrian stepping into the roadway, this approach is compatible with crossing indicator studies, where the participants merely indicate when they would cross, rather than actually stepping into the roadway. The CAPS framework therefore allows for a more objective and consistent safety assessment of pedestrian crossings in a research context without having pedestrians physically step into the roadway.
Past research has documented that pedestrian crossings at modern roundabouts can result in an impedance effect on the available capacity of entering traffic. The magnitude of this impedance effect is intuitively linked to the allocation of rights-of-way at the crosswalk, where a greater likelihood of driver yielding is expected to affect capacity more severely. However, existing pedestrian impedance models in the 2010 Highway Capacity Manual and the FHWA Roundabout Guide are not sensitive to yielding rates. The principal objective of this paper is to quantify pedestrian impedance effects on the vehicular entry capacity at multi-lane roundabouts as a function of driver yielding behavior. A calibrated microsimulation model is used to develop the relationships and explore changes in volume and yielding parameters. Impedance models are further developed for the pedestrian hybrid beacon (PHB) treatment, which is gaining increasing attention at multi-lane roundabouts across the United States. The results confirm the expected effects that the pedestrian impedance is more severe with higher pedestrian flow rates but decreases in severity with greater conflicting flows. The results further show that the effect of varying yielding rates on the impedance effect is minimal for congested roundabout approaches, because the relative effect of yielding is small compared with that of pedestrian volumes and conflicting circulating flow. The analysis of the PHB treatment shows that the impedance effect of the same pedestrian flows is generally less than that for an unsignalized crossing environment.
Calibration and validation results for modeling double-crossover diamond (DCD) interchanges in a microsimulation environment are presented. The VISSIM simulation tool and detailed field data collected at four operational DCDs in the United States help to describe modeling challenges, calibration steps, and validation results in the form of delay, travel time, and queuing estimates. DCD interchanges are rapidly being deployed across the United States, accelerated by their ability to process high volumes of especially left-turning traffic at interchanges at a greatly reduced construction cost as that of other interchange alternatives. In the absence of an analytical methodology for evaluating these interchanges, simulation currently represents the only option for evaluating the operational performance of DCDs. Although other research has applied simulation to DCD evaluation, this study is able to present detailed validation results from field data collected at four fully operational U.S. DCDs. The results show that the operations of DCDs can largely be replicated in a simulation environment but that care needs to be taken for properly setting speed and routing decisions throughout the DCD network. The analysis further show that validation is more readily achieved over an extended route analysis, with increasing difficulties for short segment validation. The validation of field-measured queues proved challenging because of definitional differences between simulated and field study results. Overall, the results demonstrate the feasibility of satisfactory calibration of simulation tools to enable the operational performance evaluation of DCD interchanges.
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