The behaviour of motorists overtaking cars and trucks of various lengths was observed and analysed to quantify the effects of these vehicle types in the traffic stream. The technique used to observe motorists was based on a system using video cameras and recorders. A series of digits were superimposed onto the video signal to enable digital information to be logged. This report describes the experimental technique, the method of extracting the data from the video tapes and the data analysis. The most important outcome from the analysis was a series of regression equations which relate the mean and variance of overtaking performance parameters (overtaking time, overtaking distance, etc.) To the length and speed of the overtaken vehicle for various overtaking manoeuvre types (flying, accelerative, single, multiple, etc.). The effects of the height and type of the overtaken vehicle and the information signs advising of long vehicles were also investigated and are reported. The distribution of safety margins, indecision times and critical gaps was also discussed. In this report, the author develops, from the regression equations, overtaking sight distances for use in road design and in the marking of no- overtaking zones. A distinction is made between the sight distance requirements for drivers to initiate overtaking manoeuvres and for drivers to be confident of completing overtaking manoeuvres. Finally, an extrapolation of the regression results to indicate the effect of road trains (articulated vehicles towing articulated trailers) in traffic streams on two- lane roads was also discussed (a). The ISBN of the microfiche version is 0-86910-044-4.
Samenvatting