Portland State University. Department of Civil and Environmental Engineering
Christopher M. Monsere
Date of Award
Master of Science (M.S.) in Civil & Environmental Engineering
Civil and Environmental Engineering
Roads -- Interchanges and intersections -- Design and construction -- Oregon, Roads -- Interchanges and intersections --Safety measures -- Oregon, Traffic accidents -- Oregon -- Statistics
This research aims to provide a preliminary update to statewide intersection crash rates for the state of Oregon using 2008-2013 crash data and a statewide sample of 129 intersections where two (or more) state-owned facilities intersect. Using intersections where state-owned facilities represent both the major and minor legs of the intersection allows for the maintenance of up-to-date intersection crash rates by eliminating time-intensive traffic volume data collection. Due to the frequency and severity of crashes at intersections, development of easily obtained intersection crash rates is important to assess trends and effectiveness of safety countermeasures employed at these locations in the current data year as well as over longer analysis periods.
This research also evaluates whether a recent crash report processing change within the Crash Analysis Reporting Unit of the Oregon Department of Transportation significantly increased intersection crash rates after the year 2011. As part of a special request, this research also provides fatal and incapacitating injury crash rates for a statewide sample of 500 intersections, calculated from 2003-2007 crash data.
Intersection crash rates were calculated for each of three analysis periods: 2003-2007, 2008-2010, and 2011-2013. The calculated rates were compared using statistical tests to determine if the statewide intersection crash rates had changed over time. The objective of this analysis was to detect if, over time intersection crash rates in the state of Oregon had changed significantly. Crash rates were calculated based on 2,731 crashes that were extracted from a sample of 129 intersections over an 11-year period.
To evaluate if changes that occurred with regard to crash reporting procedures within the Crash Analysis Reporting Unit manifested themselves in crash rates, statistical tests were completed to assess the rates for the analysis periods 2008-2010 and 2011-2013. The procedural change allowed approximately 5,000 additional non-fatal crashes to be added to the yearly crash database beginning in the year 2011.
Fatal and incapacitating injury crash rates were calculated using 2003-2007 crash data for a statewide sample of 500 intersections. The Transportation Planning Analysis Unit of the Oregon Department of Transportation will use the calculated rates to flag intersections within Oregon for further safety analysis provided the crash rate at the intersection exceeds the mean or 90th percentile statewide crash rate.
Preliminary results suggest that a larger sample of intersections is required in order to provide statistically representative results. Crash rates calculated from a sample made up of only intersections where two (or more) state-owned facilities intersect did not compare to a statewide sample of intersections with facilities owned by multiple jurisdictions. Due to the limited sample size, only three of the eight intersection groups were analyzed throughout the entirety of this research. The three intersection groups analyzed were rural 3-leg stop controlled (R3ST), rural 4-leg stop controlled (R4ST), and urban 4-leg signalized (U4SG) intersections.
Results for the comparison of crash rate over time show that insufficient data were available to prove evidence of significant differences in crash rates. Larger sample sizes are required to determine if intersection crash rates in the state of Oregon have changed significantly over time.
Statistically significant results were revealed for R4ST and U4SG intersection groups, highlighting the affects of the internal crash report processing change that occurred in the year 2011. The results showed that significant increases in mean crash rates were evident when comparing the two analysis periods. More data are required to determine if the results obtained in this preliminary analysis are cohesive in nature, spreading across all or the majority of intersection types.
Due to limited comparison data for the calculated fatal and incapacitating injury intersection crash rates for the state of Oregon, a comprehensive analysis of the resulting crash rates was not provided. The result of the calculated rates do show that on average, urban crash rates were 1.47 times greater than rural rates. Only one rural intersection group (R4ST) had fatal and incapacitating injury crash rates greater than its urban counterpart group (U4ST). The crash rates for the two intersection groups R4ST and U4ST were 3.661 and 0.321 (reported in crashes per 100 million entering vehicles), respectively.
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Hazel, Daniel R., "Safety at Intersections in Oregon – A Preliminary Update of Statewide Intersection Crash Rates" (2015). Civil and Environmental Engineering Master's Project Reports. 24.