An assessment of conspicuous traffic signals: mast arms

Abstract

Traffic signal conspicuity is likely to be a factor behind difficulties in detecting traffic signals. There is increasing interest in South Australia in providing mast arm mounted traffic signals at intersections to increase traffic signal conspicuity and reduce specific crash types. This report aims to review best practice principles in the conspicuity of traffic signals and determine the extent to which poor conspicuity of traffic signals contributes to crashes at signalised intersections. Without any recent Australian studies, it is difficult to determine the extent to which crashes result from a failure to detect traffic signals. According to best practice principles, the installation of additional traffic signals on mast arms at intersections has potential to improve traffic signal conspicuity. The second aim of this report is to attempt to quantify any road safety benefits in terms of crash reductions for installing additional signals, specifically traffic signals on mast arms at intersections. Research evidence from a number of evaluations shows that the installation of mast arms at intersections is associated with effects ranging from an estimated 89 per cent reduction in the total number of crashes to a 21 per cent increase in crashes. The greatest crash reductions were reported for right angle crashes (15-100%) while left turn crashes (equivalent to right turn in Australia) were associated with small crash reductions. Although this review shows that mast arms were associated with some crash reductions, it is important to note that these findings are not conclusive as many of the evaluations suffered from poor methodological design.