Four-Lane to Three-Lane Analysis

Principal Investigator:

Reginald Souleyrette, reg@iastate.edu (other projects)

Student Researchers:

• Thomas B. Stout, stouttom@iastate.edu

Other Authors: Thomas Stout

Project Status: In Progress

Start Date: 01/01/2005
End Date: 06/30/2005

Project Web Page: http://www.ctre.iastate.edu/research/4laneto3lane.htm

Related Publications:

• Three lanes really can be safer than four, Technology News, 06/01/2006
• Four-Lane to Three-Lane Conversions, Tech transfer summary, 04/30/2006

Research Objective: The safety impacts of the conversion of a 4-lane undivided roadway to a 3-lane roadway are evaluated using classical before and after studies, with yoked pairs and the cities of some 14 sites. Iowa DOT databases were used to evaluate the changes in the frequency of crashes, rate of crashes, types of injuries, major causes of crashes, key age groups, single vehicle run-off-road crashes, and direction of travel coupled with initial action. The results indicated that the frequency of crashes was reduced by about 26%, when other changes were accounted for, that serious injuries were reduced, and that older drivers had a reduced risk of crashing

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