Synthesis of Safety for Traffic Operations - Transports Canada

Synthesis of Safety for Traffic Operations March 2003
Region of Halton (2001)
The Region of Halton, Ontario has also developed SPFs for their signalized and
unsignalized intersections, disaggregated by severity. These SPFs can be used to
estimate the safety impacts of signalization through comparison. The form of the SPFs
are as per Equation 3.14, the parameters are estimated in Table 3.15 and 3.16 for
signalized and unsignalized intersections, respectively.
N = a TOTAL b1 RATIO b2 [3.14]
where:
TOTAL = AADT main + AADT minor
RATIO = AADT minor / TOTAL
AADT main = Average daily traffic entering from the main road
AADT minor =Average daily traffic entering from the minor road
TABLE 3.15: Region of Halton – Signalized intersections
a
Type Environment
b
Fatal+Injury PDO 1 b 2
3-leg All 7.0E-5 2.5E-4 0.934 0.165
Urban/Suburban 8.1E-3 2.32E-2 0.591 0.688
4-leg
Rural 1.04E-3 3.16E-3 0.581 -0.940
TABLE 3.16: Region of Halton – Unsignalized intersections
Type Environment
a
Fatal+Injury PDO
b 1 b 2
3-leg All 2.5E-3 7.32E-3 0.614 0.5253
4-leg All 7.2E-4 1.64E-3 0.838 0.591
Thomas and Smith (2001)
Thomas and Smith (2001) undertook an examination of the safety impacts of
signalization at 16 intersections in various municipalities in Iowa. The site selection
process is not described; the study methodology is a naïve before-after analysis using
crash frequency and severity. The crash frequency is comprised of three years of before
and three years of after data categorized by severity, and several impact types. Some
“outliers” were removed from the data set, as they were skewing the results. The results
are shown in Table 3.17.
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