Abstract:
Over the past couple of decades, Iowa has converted several 4-lane urban roadways to 3-lane sections. Most of these have been on low volume roads in smaller communities. Recently, multiple analyses, both standard before-after and Bayesian, have been conducted to explore the safety and operational impacts of these conversions or road diets. Each of these analyses have shown positive impacts of the 4-lane to 3-lane conversions in Iowa. As a couple of years have passed since the initial analyses and as the Bayesian analysis had not considered severity concerns, the analysis was updated with these additional years to extend the after periods for the sites and to include a severity analysis. Within this paper, the results of these latter analyses are explored, with emphases on the data, results, and possible future applications of these conversions. Relative to total crash history, results indicate a 25.2% reduction in crash frequency per mile and an 18.8% reduction in crash rate.
