PREDICTION OF GAP ACCEPTANCE BEHAVIOUR AT TRAFFIC CIRCLES - RECENT FINDINGS

This paper presents some new findings on the nature of gap acceptance behaviour at traffic circles which have been obtained in the course of developing a simulation model to predict delay at such intersections. During the collection of time gap acceptance behaviour, the behaviour of drivers appeared to be influenced by the behaviour of vehicles on the adjacent upstream approach. Consequently, it was decided to categorize gaps/lags according to whether a conflicting vehicle had originated from the adjacent or a previous approach. The introduction of the "refinement" tended to improve the correlation between observed and simulated delays. The effect of the actual position of a conflicting vehicle on the gap acceptance behaviour led to the notion to use distance as opposed to times to quantify gaps/lags. The accuracy of using distance as opposed to time-based gaps/lags was tested using the (modified) simulation model and observed delays. It was found that in general, the correlation between observed and simulated results was better when using distance-based gaps/lags. Deriving critical distances from observation proved to be a time-consuming exercise and the possibility of using distances related to the geometric characteristics of a circle was investigated. Preliminary results using this technique gave favourable results providing that the approaches to the circle were spaced at approximately 90 degrees.