Synthesis of Safety for Traffic Operations - Transports Canada

Synthesis of Safety for Traffic Operations March 2003
Lalani does not account for exposure in the safety analysis but reports that traffic
volumes in the city increase at an average rate of 6% per annum.
Traffic Signal Timing
Greiwe (1986)
The City of Indianapolis, Indiana evaluated the safety impacts of converting two-phase
signal operation to a split-phase left-turn sequence as shown in Figure 3.2 (Greiwe,
1986). No indication is given as to the site selection process. The study methodology
included a naïve before-after study of crash frequency with two-years of before, and a
minimum of one-year of after data. Target crashes were left-turn, right-angle, and rearend
crashes. It is noted by the author that traffic volumes remained nearly the same
throughout the study period, so adjustments for exposure were not required.
FIGURE 3.2: Split Phasing for Left-turns
The results of the analysis are shown in Table 3.43.
TABLE 3.43: Safety Impacts of Split Phasing for Left-turns
Site
Before
After
LT RA RE Other All LT RA RE Other All
1 4 1 2 3 10 1 1 1 1 4
2 16 3 1 2 22 2 1 2 1 6
3 16 3 11 1 31 5 2 6 3 16
4 4 0 0 2 6 0 0 0 1 1
5 5 1 6 1 13 2 1 5 0 8
6 9 2 2 3 16 2 0 2 1 5
7 4 2 1 0 7 0 2 0 2 4
8 19 0 6 5 30 5 1 6 6 18
Total 77 12 29 17 135 17 8 22 15 62
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