Spatial and Temporal Analysis of Driver Gap Acceptance Behavior at Modern Roundabouts

Despite an increasing acceptance of modern roundabouts in the United States, unfamiliarity with this type of intersection is still widespread. This unfamiliarity results in drivers making unpredictable decisions about gap acceptance, thus increasing the difficulty of design decisions. The relationship between the spatial and temporal critical gaps accepted by drivers in modern roundabouts is explored with gap acceptance data from more than 1,500 vehicle interactions at the roundabout on the University of Massachusetts, Amherst, campus. The critical gap was determined to be 42 ft spatially and 2.2 s temporally, which correlated directly with the average speed of the circulating flow. A longer critical gap time was observed for heavy vehicles in the traffic stream. Even though the unidirectional flow of the circulating traffic creates a potentially unpredictable environment for the driver, careful and precise analysis to obtain an accurate and reliable value of the critical gap will allow for improved roundabout design.