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South Dakota Department of Transportation
Project Synopsis
SD2004-06


Title: Updating South Dakota Crash Frequencies and Crash Reduction Factors
Project Researcher: Stephanie Mutschler,
Project Manager: Hal Rumpca
Research Period: -
Status:
Cost: $0.00

Problem Statement:South Dakota needs to update the expected value analysis tables for accident data collected from random intersections located throughout the state. An expected value analysis table provides the expected number of accidents for a given intersection type and accident type. The expected values provide a standard for identifying abnormal accident rates in consideration of local roadways, drivers, and environmental conditions. SDDOT last updated these factors in 1998, in study SD1998-12, "Development of South Dakota Accident Reduction Factors". Updated tables could be used to improve identification of serious safety problems at intersections in South Dakota, and to determine if an intersection should be considered hazardous in relation to the frequency of a particular type of accident such as a head on collision.

There is also a need to determine if the Roadway Safety Improvement (RSI) Projects completed from 1986 to 2000 have actually reduced accidents. Accident Reduction Factors (ARFs) are values used to determine the degree to which accidents decrease after an improvement project. A Severity Reduction Ratio (SRR) is a ratio of average accident severity before an improvement project to the average accident severity after an improvement project. A SRR of less than 1 indicates a reduction in the average severity of accidents following an improvement project. The SD1998-13 Project "Development of South Dakota Accident Reduction Factors" computed sixty-two ARFs and SRRs. However, it was decided that South Dakota should rely on reduction factors from other states to calculate benefit/cost ratios until the South Dakota Accident Reduction Factors are performed on a minimum of ten accident locations per type of improvement. Research is needed to review South Dakota RSI Project information to compare accident data for a three-year period before a project started to a three-year period after the project was completed. The resulting data can then be used to update Accident Reduction Factors and Severity Reduction Ratios for South Dakota by calculating the factors from at least ten accident locations for each type of improvement.

In 2000, the State Legislature raised the threshold for reportable accidents. Prior to that time, property- damage-only accidents generating $500 or more damage to an individuals property or accumulated property damage of $1,000 or more per accident were required to be reported. Since July 1, 2000, only those property-damage-only accidents generating $1,000 or more damage to an individuals property or accumulated property damage of $2,000 or more per accident are required to be reported. (Note: These changes do not affect the reporting of fatal and non-fatal injury accidents). RSI Project information needs to be updated and documented so that the data used to develop accident reduction factors remains consistent and can be used even though the reporting thresholds have changed.



Findings: The researcher used accident data gathered from South Dakota Roadway Safety Improvement projects during the 1994 to 2000 time frame to calculate the Accident Reduction Factors and Severity Reduction Ratios. The researcher updated the Severity Reduction Ratio formula with the most recent FHWA accident severity values. A benefit/cost analysis was performed on the Roadway Safety Improvement projects to determine their cost effectiveness. The Expected Value Analysis tables were updated in 2005 by Research Intern Stephanie Mutschler.

Research Objectives:
1  Calculate Accident Reduction Factors and Severity Reduction Ratios for each Roadway Safety Improvement Project completed between 1994 and 2000.
2  Calculate average Accident Reduction Factors and Severity Reduction Ratios for each RSI improvement type used by the SDDOT.
3  Recommend Accident Reduction Factors and Severity Reduction Ratios to be used in RSI selections.
4  Update the South Dakota Expected Value Analysis Tables of accident frequencies at various intersection types.

Research Tasks:
1  Meet with the project's technical panel to review the project scope and work plan.
2  Review and summarize literature pertinent to abnormal accident pattern evaluations, Accident Reduction Factors, and Severity Reduction Ratios.
3  Develop a phone survey and contact State DOT's in the Upper-Midwest region to determine if they have developed and used expected value analysis tables, Accident Reduction Factors, and Severity Reduction Ratios.
4  Develop a list of South Dakota RSI Projects completed since 1986 including project location boundaries and types of improvements. Generate three-year before and after RSI accident summaries for each project completed from 1986 to 2000.
5  Using the information from RSI accident summaries from each project and the latest FHWA specified dollar values for fatalities, injuries, and property damage only crashes, update the Accident Reduction Factors (ARF's) and the Severity Reduction Formu
6  Calculae the benefit/cost ratios of projects completed with RSI funding only.
7  Recommend the Accident Reduction Factors and Severity Reduction Ratios to be used in South Dakota.
8  Obtain accident, traffic volume, and other data from the SDDOT and local units of government necessary to update the expected value analysis tables for the most current five year period.
9  Update the expected value analysis tables for South Dakota and compare them to a representative sample of similar tables developed for other states.
10  Prepare a final report and executive summary of the literature review, findings, and conclusions.
11  Make an executive presentation to the Research Review Board at the conclusion of the project.

Documents Available:
SD2004_06_Final_Report.pdf
ExpectedValueAnalysisFinalReport.pdf
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