Effect of Right Turn Phases at Signalised Intersections. Part 1 - Safety Performance
Monash University Accident Research Centre - Report #20 - 1991
Authors: B. Bui, M. Cameron, C. Foong
Full report in .pdf format [4.5MB]
This study examined the safety performance of partially and fully controlled right turn phases at signalised intersections. The objective of this study was to quantify the impacts of alternative types of right turn control in terms of safety. The evaluation of the mobility performance of these right turn signals is covered in a separate report (Part 2).
The evaluation was based on a sample of 217 intersection approaches from 129 intersections where a right turn phase had been installed. This sample covered three types of changes considered in this study: no control to partially controlled right turn phase (Group 1), no control to fully controlled right turn phase (Group 2) and partially to fully controlled right turn phase (Group 3).
A "before and after" technique in conjunction with a control ratio was employed to estimate the changes in casualty accident frequencies following a change in the right turn control. A Chi-square test was used to assess the accident changes for statistical significance.
This study found that the installation of partially controlled right turn phases (Group 1) had no apparent safety benefits, either over all types of sites or when specific types of sites or times of day were considered.
The change from no control to fully controlled right turn phases (Group 2) showed a 45% reduction in all types of casualty accidents. This overall effect included reduction in Right Through (82%), Cross Traffic (48%) and Pedestrian (35%) casualty accidents. There was however a 72% increase in Rear End & Left Rear casualty accidents. This increase was also present in Group 3 (partial to full right turn control) but to a less extent and, in most cases, was not statistically significant. This aspect warrants a more detailed investigation.
The change from partially controlled to fully controlled right turn phase (Group 3) showed an overall reduction of 65% in all types of casualty accidents. Right Through and Cross Traffic casualty accidents were reduced by 93% and 51 % respectively.
This study showed that the installation of fully controlled right turn phases is a highly effective way to reduce the incidence of Right Through crashes at signalised intersections. The installation of partially controlled right turn phases had no beneficial effect on Right Through collisions.