Synthesis of Safety for Traffic Operations - Transports Canada

Conducting and Authoring Research
R =
(N t + N)n
(n t – n)N
-1 [C1]
Where:
R = Regression effect (as a decimal)
n = Number of years of crash data for the site
N = Number of crashes at the site in “n” years
N t = a 2 /(v-a)
n t = a/(v-a)
a = mean or average crash rate for a group of similar intersections
v = variance of mean crash rate for the group
For example, if a two-way stop-controlled intersection with a crash record of 12 crashes
in 3 years were treated with an all-direction stop and the crashes were reduced to 5
crashes in a 3 year period, how much of the safety benefit can be attributed to RTTM? In
order to use the correction factor, the analyst must assemble data from a group of
similarly two-way stop controlled intersections. Furthermore, it is found that the mean
crash frequency for the group is 2 crashes/year, with a variance of 0.2. Therefore:
N = 12
n = 3
N t = (2*2)/0.2-2) = -2.22
n t = 2/(0.2-2) = -1.11
R =
(-2.22 + 12)3
(-1.11 – 3)12
-1 = 0.29
The RTTM effect is estimated to be 29%. Therefore, the CMF is calculated as follows:
CMF =
5 crashes/year “after”
12 crashes/year “before” x (1-.029) correction for RTTM
= 0.59
Without the correction for RTTM the CMF would have been overestimated to be 0.42.
Authoring a Scientific Paper
It is not the intent of this section of the report to provide a comprehensive discussion on
all of the important elements of report writing. Grammar and the language of the paper
are certainly beyond the scope of this document. What is intended is for the reader to get
an understanding of the essential elements of a research paper, and some suggestions for
organizing the content.
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