Iowa's Experience with 4-Lane to 3-Lane Conversions

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.

• Corporate Authors:

  Transportation Research Board

  500 Fifth Street, NW
  Washington, DC  United States  20001
• Authors:
  • Pawlovich, Michael D
  • Li, Wen
  • Carriquiry, Alicia
  • Souleyrette, Reg
  • Stout, Tom
  • Welch, Tom
• Conference:
  • 3rd Urban Street Symposium: Uptown, Downtown, or Small Town: Designing Urban Streets That Work
  • Location: Seattle WA
  • Date: 2007-6-34 to 2007-6-27
• Publication Date: 2007

Language

• English

Media Info

• Media Type: CD-ROM
• Features: Figures; References; Tables;
• Pagination: 14p
• Monograph Title: 3rd Urban Street Symposium: Uptown, Downtown, or Small Town: Designing Urban Streets That Work, June 24-27, 2007, Seattle, Washington

Subject/Index Terms

• TRT Terms: Bayes' theorem; Before and after studies; Crash locations; Crash rates; Crash severity; Four lane highways; Highway safety; Low volume roads; Three lane highways; Traffic crashes; Urban areas
• Geographic Terms: Iowa
• Subject Areas: Design; Highways; Planning and Forecasting; Safety and Human Factors; I21: Planning of Transport Infrastructure; I82: Accidents and Transport Infrastructure;

Filing Info

• Accession Number: 01091647
• Record Type: Publication
• Files: TRIS, TRB
• Created Date: Apr 23 2008 9:26AM