United States Department of Transportation
i
Safety comparison of roadway design elements on urban collectors with access : final report, April 2009.
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2009-04-01
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[PDF-1.91 MB]
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Edition:Final report.
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Abstract:The main goal of this study identified by NJDOT can be defined as “the quantification of the effects of
management treatments on roadway operations and safety on urban collectors with access”.
Since, urban collector road runs through highly diversified areas, various factors have to be considered
when before-and-after comparisons of improvements in terms of safety are conducted in this study. For
25-40 mph urban collectors with access, these are:
1. Increase in lane widths (10' or 11' to 12'),
2. Construction of 4,6,8, or 10 foot shoulders,
3. Removal of trees in median and border areas,
4. Installation of guide rails, and vertical & horizontal geometry changes to improve sight distances.
Before and after analysis for these countermeasures was conducted via several approaches, including
naïve approach, analysis via control groups, analysis via Empirical Bayes approach, and analysis via
Full Bayes approach. After conducting before-and-after analysis, Crash Reduction Factors (CRF) were
estimated for each countermeasure. The individual CRF values and their relative order among different
countermeasures are similar to the values in the literature. In particular, improvements in vertical and
horizontal alignment results in highest reduction in the accident rate, followed by adding shoulders,
median barrier installation, lane width increase, and guide rail installation.
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