Intersection approach speed and accident probability

Abstract

A statistical model is derived for gap acceptance at intersections, taking into account limitations of human perception. The model assumes the logarithm of the odds for acceptance of a gap as a linear function of the logarithms of gap time and the speed of the vehicle closing the gap. Fitting is performed against gap acceptance decisions as observed in real traffic at 12 unsignalized intersections by Brilon and Weinert (2001) [Ermittlung aktueller grenz- und folgezeitlucken fur auerortsknoten ohne lichtsignalanlagen. Strasenbau und Strasenverkehrstechnik, vol. 828.] and in a driving simulator experiment by Hancock and Caird (1993) [Factors affecting older drivers’ left turn decisions. Technical Report, Transportation Research Board, National Research Council, Washington, DC]. The model fit was reasonable for the traffic observations (R2 = 0.76) and very good for the simulator data (R2 = 0.97). Parameter estimation yields that the speed has a significant effect on gap acceptance behavior. Drivers crossing a priority stream tend to accept shorter time gaps as the speed of the approaching vehicle increases. This effect is stronger for older drivers than for younger drivers. It is proposed that this model may be extrapolated to quantify the relation between approach speed and accident probability. The validation that this kind of extrapolation would require, has not yet been performed. Keywords: Accident probability; Accident reconstruction; Conflict rate; Crossing behavior; Gap acceptance; Intersection accidents; Speeding