Synthesis of Safety for Traffic Operations - Transports Canada

Intersection Control
where:
X1 = 0 if main road left-turns are permitted; 1 otherwise
X2 = Average lane width on main road (metres)
X3 = 1 if the number of lanes on main road is 3 or less;
0 otherwise
X4 = 1 if the number of lanes on main road is 4 or 5; 0 otherwise
X5 = 1 if no access control on main road; 0 otherwise
X6 = 1 if right-turn is NOT free flow from main road; 0 otherwise
X7 = 1 if no illumination; 0 otherwise
X8 = 1 if the main road is a minor arterial; 0 otherwise
X9 = 1 if the main road is a major collector; 0 otherwise
Signal-controlled
N = 0.032452 ADT main 0.503 ADT side
0.224
e 0.063X1 e 0.622X2 e -0.200X3 e -0.310X4 e -0.130X5
e -0.053X6 e -0.115X7 e -0.225X8 e -0.130X9 [3.8]
where:
X1 = 1 if pre-timed signal; 0 otherwise
X2 = 1 if fully-actuated signal; 0 otherwise
X3 = 0 if two-phase signal; 1 otherwise
X4 = 1 if no access control on main road; 0 otherwise
X5 = 1 if 3 or less lanes on the side road; 0 otherwise
X6 = Average lane width on main road (metres)
X7 = 0 if no free flow right turn from main road; 1 otherwise
X8 = 1 if 3 or less lanes on the main road; 0 otherwise
X9 = 1 if 4 or 5 lanes on the main road; 0 otherwise
These models can be used to determine the impacts of signalization (or the removal of a
signal). Caution should be exercised in relying solely on the prediction models. First of
all, it is a better estimate of the long-term safety of a facility if the results of the
prediction model can be combined with the actual safety performance (i.e., crash history)
of the site. Secondly, there are some aspects of the above models that seem to be
counterintuitive. For instance, in the model for stop-controlled intersections, controls on
access, and the provision of illumination are seen to be detrimental to safety (CMFs of
1.55 and 1.17, respectively). The conventional wisdom disagrees with these findings and
casts some doubt on the usefulness of these equations.
Harwood et al (2000)
Harwood et al (2000) also developed SPFs for cross intersections of two-lane roads in
rural settings. The models are as follows:
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