Crash Analysis

Research papers - Iowa's four- to three-lane analysis efforts

EB/FB Comparison

Safety Impacts of "Road Diets" in Iowa (2005 studies combined)
Paper (PDF) 
July 2005
A draft copy of a paper being prepared for consideration for publication in the ITE Journal (combines the results from the two 2005 studies above).

The Effect of Four- to Three-Lane Conversion on the Number of Crashes and Crash Rates in Iowa Roads (2005)
Project report (PDF) 
June 2005
We analyze crash data collected by the Iowa DOT using Bayesian methods. The data set includes monthly crash numbers, estimated monthly traffic volumes, site length and other information collected at 30 paired sites in Iowa over more than 20 years during which an intervention experiment was set up.

A summary submitted to the 2005 Mid-Continent Transportation Research Symposium, August 18-19, 2005, Ames, Iowa for an invited presentation on the topic:
Abstract As part of a ISU statistics department creative component in cooperation with Iowa DOT's Office of Traffic and Safety, a full Bayes analysis of the reduction in crash frequency due to four-lane to three-lane conversions in Iowa.

Before and After Study of Some Impacts of four- to 3-lane Roadway Conversions (2005)
Project report 
March 2005
The focus of this research has been to evaluate the safety impacts of the conversion of 14 roadways from a four-lane undivided configuration to a three-lane configuration with one through lane in each direction and a two-way left-turn lane.

Abstract The safety impacts of the conversion of a four-lane undivided roadway to a three-lane roadway are evaluated using classical before and after studies, of some 14 sites using yoked comparison pairs and a comparison to the cities in which the sites are located.

Guidelines for the Conversion of Four-lane Undivided Roadways to three-lane Two-Way Left-Turn Lane Facilities (2001)
Project report (PDF) 
April 2001
Sponsored by the Iowa DOT's Office of Traffic and Safety of the Iowa Department of Transportation CTRE Management Project 99-54
Project Web page Related publications and presentations linked from project Web page
Office of Traffic and Safety
Ph: 515-239-1557 | Fax: 515-239-1891

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