United States Department of Transportation
i
Enhancing NDOT's Traffic Safety Programs
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2013-10-01
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[PDF-3.50 MB]
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TRIS Online Accession Number:01651146
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Edition:Research Report
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Abstract:This report summarizes three tasks of the UTC project. Firstly, the report presents the SPF calibration procedures and results for rural two-way two-lane roads. A calibration factor was found to be 1.21 for both total and Fatal and Injury crashes. In addition, the performance of the existing (un-calibrated) HSM SPF and the calibrated HSM SPF was compared using a variety of statistical GOF tests and also the CURE plots. The comparison results indicate that the calibrated HSM SPF exhibited a better fit to the local data than the un-calibrated HSM SPF. Nevertheless, the calibrated HSM SPF was not determined as a good-fitting model. Therefore, further research needs to be done to develop Nevada specific SPF to better represent the observed crash frequency. Secondly, the report summarizes the procedures and methodologies for conducting a before-and-after study. Four commonly used before-and-after study approaches are discussed including the Naïve approach, the Comparison Group approach, the Yoked Comparison as well as the Empirical Bayes method. This task provides a concise introduction of the concepts, merits and limitations of each approach to weigh into the decision process where data availability, resources, and other decisive factors are realities. This report recommends that NDOT develop related training materials and conduct training sessions for NDOT and local government traffic engineers in using the recommended methods. The third part of this report is a safety evaluation study on the new section of I-580 and the U.S. 395A. The analysis contains an overview of the roadway segments, and examines the horizontal alignment, vertical alignment and cross-section in more detail through a review of the detailed design plan/profile data. The EB method that weights the observed crash frequencies with the predicted crash frequencies using the base SPFs and CMFs is applied to calculate the expected crash frequencies of U.S. 395A and old U.S. 395 road segments. The freeway predictive method documented in the future Chapter 18 of HSM is applied to predict the safety of I-580 in 2014 as well. The evaluation results indicate that in 2014 53 crashes are predicted to occur along the new I-580 freeway section. In addition, 14 crashes are expected to occur along the U.S. 395A segments. The safety of the old U.S. 395/U.S. 395A will be improved significantly given the historical crash records involved approximate 69 crashes per year from 2007 to 2011 and a total of 72 crashes expected in 2014 without the building of the new freeway section. A benefit cost analysis was conducted for the I-580 Freeway Extension Project and the Benefit-Cost Ratio (BCR) of 1.76 was obtained. In the long run, the project will produce economic benefits in accident reductions, travel time savings, vehicle emission reductions, etc.
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