4-to-3 Lane Conversion

4 to 3 Lane Conversion
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What Is A 4- To 3-Lane Conversion?

A 4- to 3-lane conversion (a type of road diet) involves restriping a 4-lane road as a 3-lane road. One lane is provided in each direction with a continuous left turn lane down the center. This often leaves room left over which can be used for enhancements such as parking or bike lanes. When combined with a roadway resurfacing project, a 4- to 3-lane conversion can be completed without any additional cost. 4- to 3-lane conversions are one of the Federal Highway Administration’s (FHWA’s) 20 proven safety countermeasures.

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What Are the Benefits of a 4- To 3-Lane Conversion?

  • Shown to reduce crashes by about half.
  • Decreases left-turn and rear-end crashes because of the dedicated center turn lane.
  • Opportunity to provide enhancements such as parking or bike lanes.
  • Improves walkability - fewer lanes for pedestrians to cross, and traffic is located farther from the sidewalk.
  • Easier access to homes, schools, and businesses.
  • Regulates speeds and calms traffic. Speeds are more consistent with just one lane in each direction.
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When Should a 4- to 3-Lane Conversion Be Considered?

There are many factors that should be considered before implementing a 4- to 3-lane conversion. Some of the factors that the Iowa DOT considers are:

  • Traffic volume
  • Number of intersections
  • Type and location of access points
  • The corridor’s crash history

Many communities in Iowa have had success implementing 3-lane roads in urban, suburban, and rural locations.

To proactively identify where future conversions might be considered, the Iowa DOT recently conducted a statewide screening. This effort provided a snapshot of potential locations where a conversion might be successful.

4- to 3-lane Conversion Myths

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4-to-3 Lane Resources

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