Synthesis of Safety for Traffic Operations - Transports Canada

Synthesis of Safety for Traffic Operations March 2003
• Pedestrian flow
• Safety problem being addressed (target crashes)
• Description of the treatment
• Number of crashes by severity in the before and after periods
The manner in which MOLASSES sites are selected for treatment is unknown.
Therefore, regression-to-the-mean effects may cause efficacy estimates to be inflated. In
addition, the estimates are based on before-after studies of crash frequency. There is a
failure to account for changes in exposure or other potential confounding factors.
Limited information is available from the MOLASSES database without sending a
tailored request to the TRL. Nonetheless, the safety impacts of new signals in urban
areas, and in rural areas are as shown in Table 3.11.
TABLE 3.11: Safety Effects of Signal Installation in the United Kingdom
Setting
Number of Number of Crashes
Installations Before After
CMF
Urban 26 323 144 0.45
Rural 8 93 20 0.22
Bauer and Harwood (2000)
Bauer and Harwood (2000) developed SPFs for urban, four-leg intersections using three
years of crash and infrastructure data from California. Lognormal and loglinear
regression was performed on the dataset described in Table 3.12.
TABLE 3.12: Intersection Characteristics for SPFs from California
Characteristic Stop-controlled Signal-controlled
No. of intersections 1342 1306
ADT
Major 1100 – 79000 2400 – 79000
Minor 100 – 16940 101 – 48000
Mean No. of
All 7.4 23.4
Crashes Fatal+Injury 3.3 9.6
The regression analysis yielded the SPFs in Equations 3.7 and 3.8.
Stop-controlled
N = 0.009429 ADT main 0.620 ADT side
0.281
e -0.941X1 e -0.097X2 e 0.401X3 e 0.120X4 e -0.437X5
e -0.384X6 e -0.160X7 e -0.153X8 e -0.229X9 [3.7]
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