Four-Lane to Three-Lane Analysis

Project status


Start date: 01/01/05
End date: 06/30/05


Principal investigators:

Student researcher:

  • Thomas B. Stout

About the research

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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Related publications:


Sponsor(s): Iowa Department of Transportation