Effects of signalisation on four-arm urban junction safety.

This paper investigates the effect of signalisation on safety of urban priority controlled four-arm junctions. Forty-eight such junctions were carefully selected to have different values for the geometric and traffic characteristics that may influence the safety effects of signalisation. Long periods before and after signalisation were considered so that the effect of the regression to the mean phenomenon becomes negligible. Signalisation was found either to increase the junction safety or to leave it unchanged. Discriminant analysis showed that among numerous variables considered those significantly influencing the effects of signalisation on safety are the flow weighted average width per arm, the flow weighted average grade per stream, and a function of the product of the conflicting stream flows of the junction. The discriminant function developed predicts quite satisfactorily the behaviour of junction safety after signalisation.

Establishing relationships between accidents and flows at urban priority road junctions.

This papers explores the effects of traffic stream flows on accident potential at urban priority-controlled (i.e. unsignalized), four-arm junctions. Forty-three urban priority junctions were carefully selected so that other than flow parameters expected to influence accident potential have similar values at the junctions considered. Using traffic accident data for five-year time periods and the corresponding 24-hour flows, a new exposure index is proposed consisting of an expression of the flows of the junction's interacting traffic streams. The regression of this exposure index on the expected number of accidents per year at junctions of the type examined yields a quite satisfactory correlation coefficient, better than those achieved when other proposed indices are used.