Synthesis of Safety for Traffic Operations - Transports Canada

Intersection Control
TABLE 3.17: CMFs for Signalization (Thomas and Smith)
Crash Type Mean # Sites
90% Confidence Intervals
Lower Upper
Fatal N/A 0 N/A N/A
Major 0.57 7 1.29 0.00
Severity Minor 0.92 16 1.42 0.43
Possible 1.44 13 2.00 0.88
PDO 0.60 14 0.71 0.48
Right-angle 0.25 15 0.34 0.16
Impact Type
Rear-end 0.96 12 1.25 0.68
Left-turn 1.27 12 1.82 0.71
Other 0.70 15 0.92 0.48
Total 0.73 15 0.93 0.53
It is evident from the results that under a 90% level of confidence, safety benefits can be
expected for PDO, right-angle, other, and total crashes. All other crash types have
confidence intervals that straddle unity (one CMF on either side of “1”). This indicates
that we are unsure if these crash types are positively or negatively impacted by
signalization.
Exposure was not accounted for in the analysis, as this data was not readily available.
In the same study Thomas and Smith also evaluated the safety impacts of signalization in
conjunction with the addition of turn lane(s). A similar methodology was used to
evaluate 11 sites. The results are shown in Table 3.18.
TABLE 3.18: CMFs for Signalization Plus Turn Lane Construction (Thomas and
Smith)
Crash Type Mean # Sites
90% Confidence Intervals
Lower Upper
Fatal 0.00 3 N/A N/A
Major 0.00 9 N/A N/A
Severity Minor 0.34 8 0.45 0.23
Possible 0.73 11 1.13 0.34
PDO 0.94 11 1.32 0.57
Right-angle 0.37 11 0.52 0.22
Impact Type
Rear-end 1.44 11 2.02 0.86
Left-turn 0.65 11 0.00 0.30
Other 0.83 11 1.16 0.50
All crashes 0.80 11 1.12 0.49
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