Synthesis of Safety for Traffic Operations - Transports Canada

Turn Lanes
Vogt determined that a left-turn lane on the major road at a stop-controlled, rural
intersection with four approaches is associated with a CMF of 0.62. For the other two
types of intersections it was found that left-turn lanes on the major road are either not
significantly correlated with crash occurrence, or were positively correlated with some
other variable under consideration, and did not exhibit an apparent safety effect. Leftturn
lanes on the minor roads at all three types of intersections had no safety impact of
were cross-correlated with another variable.
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 turn lanes to the main street
approaches at the intersections of rural, two-lane highways. The panel opined that CMFs
for left-turn lanes are as shown in Table 9.5.
TABLE 9.5: Crash Modification Factors for Left-turn Lanes
Number of main street approaches on
Intersection Traffic
which left-turn lanes are added
Type
Control
One Approach Both Approaches
Stop 0.78 ---
Three-leg
Signal 0.85 ---
Stop 0.76 0.58
Four-leg
Signal 0.82 0.67
Rimiller et al (2001)
The safety benefits of left-turn lanes were studied at 13 intersections in Connecticut by
Rimiller et al (2001). Using an Empirical Bayes model to account for regression-to-themean
effects, Rimiller examined the crash data from 1989 to 1998, inclusive at 13
intersections that were categorized by population density, intersection control, number of
approaches, and number of lanes. The results are shown in Table 9.6.
TABLE 9.6: Safety Impacts of Left-turn Lanes (Rimiller, 2001)
Control Legs Lanes No. Sites AADT CMF
Signal 4 2 1 7,500 0.41
Signal 4 4 6 21-43k 0.65
Signal 3 4 2 24-25k 0.61
Unsignal. 3 2 1 13600 0.51
Signal 3 4 (Div) 1 25000 0.98
Signal 3 2 1 16400 0.47
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