Synthesis of Safety for Traffic Operations - Transports Canada

Synthesis of Safety for Traffic Operations March 2003
It is curious to note that the right-turn channelization in urban areas is associated with an
increase in crashes.
Harwood et al (2000)
Harwood et al (2000) using an expert panel of road safety professionals reviewed the
available evidence on the safety impacts of adding right turn lanes to the main street
approaches at the intersections of rural, two-lane highways. The panel opined that CMFs
for right-turn lanes are as shown in Table 9.16.
TABLE 9.16: CMFs for Right Turn Lanes
Number of main street approaches on
Traffic
which right-turn lanes are added
Control
One Approach Both Approaches
Stop 0.95 0.90
Signal 0.975 0.95
Chin and Quddus (2001)
Chin and Quddus (2001) in analysing four-legged signalized intersections in Singapore,
Japan found that right turn lanes on both approaches increased crash frequency by 38%
(CMF=1.38), and left-turn lanes on both approaches decreases crash frequency by 53%
(CMF=0.47) 5 .
Harwood et al (2002)
In a comprehensive analysis of the safety impacts of left- and right-turn lanes, Harwood
et al (2002) conducted before-after studies for intersection improvements in eight states.
A total of 280 sites were treated and 300 sites were used as comparison or reference sites.
The sites were in urban and rural settings and were either two-way stop controlled, or
signalized (i.e., all-way stop controlled sites were excluded from the analysis). All sites
had either three or four approaches; all approaches were public streets (i.e., no private
driveways were included in the sites).
The Harwood et al study employed three different evaluation methods: the matched-pair
approach, the before-after evaluation with a comparison group, and the before-after study
using Empirical Bayes methods. Crashes that were included in the analysis are those that
5 The rules of the road in Singapore require driving to the left of the centreline. Therefore, in the Chin and
Quddus article, right-turns are equivalent to left-turns in Canada and have been adjusted accordingly.
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