Road Diets Safety

Road Diet Safety

A "road diet" is converting a roadway from four lanes to three lanes (one through lane in

each direction and a two-way, continuous left-turn lane), is frequently suggested as a traffic

calming solution or to address left-turn related crashes on undivided four-lane urban roadways

where widening may not be an option (Wikipedia, 2006).

A data analysis to assess the reduction in crash history due to "road diets" in Iowa was conducted by Iowa State University (ISU) in cooperation with Iowa Department of Transportation Office of Traffic and Safety (TAS). The study utilized monthly crash data and estimated volumes obtained from TAS for 30 sites, 15 treatments and 15 controls, over 23 years (1982-2004). The sites had volumes ranging from 2,030 to 15,350 during that time span and were largely located in smaller urbanized areas.

The main research objective was to assess whether "road diets" appear to result in crash reductions in Iowa roads. To meet the objectives ISU and TAS analyzed crash data at each site before and after the