Converting Four-Lane Undivided Roads to Three Lanes: A Low Cost Safety Improvement


Undivided roadways often experience a large number of crashes – especially between high-speed through traffic, left-turning vehicles, and other road users. One treatment for addressing this safety concern along four-lane undivided roadways is to convert the cross section to three-lanes (one type of Road Diet). This type of conversion typically involves removing or narrowing motor vehicle lanes and utilizing the space for other uses, including but not limited to a two-way left-turn lane (TWLTL), non-motorized travel modes, or parking.

FHWA, in cooperation with the Iowa DOT, is pleased to offer a one-day workshop on this low-cost, proven safety countermeasure that explores how agencies can convert four-lane undivided roadways to three lanes to improve safety, operations, and livability in their communities.

Participants will be introduced to the FHWA Road Diet Informational Guide and guided through a decision-making process to determine when this type of conversion may be a good solution.

Who Should Attend?

  • Transportation engineers and planners
  • Pedestrian & bicycle and Safe Routes to School program coordinators
  • Local police, fire, EMS and transit personnel
  • Community leaders

Workshop Learning Outcomes

  • Learn about the different types of Road Diets and why they work.
  • Understand the characteristics that make these type of conversions the right choice.
  • Identify roads that are good candidates for cross section conversion.
  • Learn what segment and intersection design elements are affected by cross section reconfigurations.
  • Practice reallocating street space for other uses, including non-motorized user needs.

Typical Workshop Agenda

8:15 a.m.
Introduction and Overview
Determining Feasibility
Design Considerations
Determining Effectiveness
Case Study Exercise(s)

12:00 p.m.

4:00 p.m.

For More Information

If you have questions or need more information, please contact Keith Knapp at 515-294-8817 or