U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
A roadway reconfiguration known as a Road Diet offers several high-value improvements at a low cost when applied to traditional four-lane undivided highways. In addition to low cost, the primary benefits of a Road Diet include enhanced safety, mobility and access for all road users and a "complete streets" environment to accommodate a variety of transportation modes.
A classic Road Diet typically involves converting an existing four-lane, undivided roadway segment to a three-lane segment consisting of two through lanes and a center, two-way left-turn lane.
Road Diet on Edgewater Drive, Orlando, Florida
The resulting benefits include a crash reduction of 19 to 47 percent, reduced vehicle speed differential, improved mobility and access by all road users, and integration of the roadway into surrounding uses that results in an enhanced quality of life. A key feature of a Road Diet is that it allows reclaimed space to be allocated for other uses, such as turn lanes, bus lanes, pedestrian refuge islands, bike lanes, sidewalks, bus shelters, parking or landscaping.
Why consider a Road Diet? Four-lane undivided highways experience relatively high crash frequencies — especially as traffic volumes and turning movements increase over time — resulting in conflicts between high-speed through traffic, left-turning vehicles and other road users. FHWA has deemed Road Diets a proven safety countermeasure and promotes them as a safety-focused design alternative to a traditional four-lane, undivided roadway. Road Diet-related crash modification factors are also available for use in safety countermeasure benefit-cost analysis.
As more communities desire "complete streets" and more livable spaces, they look to agencies to find opportunities to better integrate pedestrian and bicycle facilities and transit options along their corridors. When a Road Diet is planned in conjunction with reconstruction or simple overlay projects, the safety and operational benefits are achieved essentially for the cost of restriping. A Road Diet is a low-cost solution that addresses safety concerns and benefits all road users — a win-win for quality of life.
Road Diets stand the test of time, having been implemented by transportation agencies for more than three decades. One of the first installations of a Road Diet was in 1979 in Billings, Montana. Road Diets increased in popularity in the 1990s. Cities, including Charlotte, Chicago, New York, Palo Alto, San Francisco and Seattle, have also opted for the positive impact Road Diets bring to their communities.
FHWA developed a Road Diet Informational Guide to help communities understand the safety and operational benefits and determine if Road Diets may be helpful in their location.
Road Diets and Speed Management
Setting appropriate speed limits is an essential element of highway safety. A rationally determined speed limit is one that is safe, considered appropriate by most drivers, and enforceable. USLIMITS2 provides a fact-based set of decision rules to determine an appropriate speed limit for a specific roadway segment. USLIMITS2 is a user-friendly and logical web-based tool designed to help practitioners set credible, consistent, and enforceable speed limits. As such, USLIMITS2 is a useful tool for road diet applications. USLIMITS2 can be used for a speed study to check if existing speed limit was set appropriately and identify speeding related safety problems when managing speed is one of the purposes for a road diet application. In addition, USLIMITS2 can be used to examine if a different speed limit should be applied after road diet is done. To use USLIMITS2, please go to USLIMITS2 website at: http://safety.fhwa.dot.gov/uslimits/.
"Going on a Road Diet," article in September/October 2011 Public Roads magazine