Abstract

Contrary to traditional thinking and driver intuition, here we show that there is no benefit to ground vehicles increasing their packing density at stoppages. By systematically controlling the packing density of vehicles queued at a traffic light on a Smart Road, drone footage revealed that the benefit of an initial increase in displacement for close-packed vehicles is completely offset by the lag time inherent to changing back into a ‘liquid phase’ when flowresumes. This lag is analogous to the thermodynamic concept of the latent heat of fusion, as the ‘temperature’ (kinetic energy) of the vehicles cannot increase until the traffic ‘melts’ into the liquid phase.These findings suggest that in situations where gridlock is not an issue, drivers should not decrease their spacing during stoppages in order to lessen the likelihood of collisions with no loss in flowefficiency. In contrast, motion capture experiments of a line of people walking from rest showed higher flow efficiency with increased packing densities, indicating that the importance of latent heat becomes trivial for slower moving systems. Department of Biomedical Engineering and Mechanics at Virginia Tech Institute for Creativity, Arts, and Technology Document type: Article

Abstract

Over the past few years the population of older drivers has substantially increased across the United States. Older drivers are a group of special interest because of their potential age-related deficiencies. It is essential to understand their driving behavior and adjust the conditions of roadway systems according to their requirements. Likewise, driving behavior of older drivers needs to be considered in order to adequately estimate capacities at intersections. In the past few years, research projects were performed by the University of South Florida to analyze the differences of driving behavior among different driver age groups. Typically, the driving behavior of older drivers was evaluated by analyzing their start-up lost time and saturation headway at signalized intersections as compared to young and mid-age driver groups. Research results were based on data collected from signalized intersections with different land-use types. These intersections are located in west and central Florida where the elderly population has been increasing rapidly in recent years. From the results it was found that the presence of older drivers significantly reduced intersection capacity at all study sites because of their higher lost times and lower saturation flow rates. Therefore, driving behavior of older drivers should be considered in designing intersections located in places with a significant older driver population. In the research, models were developed to predict start-up lost time and saturation headway values generated by older drivers. Then, the variation in capacities with an increasing percentage of older drivers in the traffic stream was modeled. Finally, adjustment factors for different percentages of older drivers were developed to adjust intersection capacity. These factors are believed to account for the presence of older drivers in the traffic stream. The adjustment factors may be used in capacity analysis and design procedures for intersections with a significant older driver population. Document type: Article