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 EDC Exchange for Local and Tribal Agencies: EDC-3’s Road Diets
April 9, 2015 from 1:00 pm to 3:00 pm Central Standard Time
Four-lane undivided highways have a history of relatively high crash rates as traffic volumes increase and as the inside lane is shared by
higher-speed through traffic and slowing-or-stopping left-turning vehicles. These types of roadways can experience the following crash
types as traffic volumes increase, including:
 Rear-end and sideswipe crashes caused by speed differential between vehicles;
 Sideswipe crashes caused by frequent and sudden lane changing between two through lanes;
 Rear-end crashes caused by left-turning vehicles stopped in the inside travel lane;
 Left-turn crashes caused by left-turning motorists who feel pressure and make a poor gap judgment to depart the through lane
 Angle crashes caused by side street traffic crossing four lanes to cross an intersection, or turning left across two lanes;
 Bicycle crashes due to a lack of available space for bicyclists to ride comfortably; and
 Pedestrian crashes due to the high number of lanes for pedestrians to cross with no refuge.
One option for addressing this safety concern is a Road Diet. The most common Road Diet configuration converts 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 (TWLTL). The
reduction of lanes allows the roadway cross section to be reallocated for other uses such as bike lanes, pedestrian refuge islands, transit
stops, or parking.
A Road Diet can be a low-cost safety solution because it can usually be installed within the existing cross section of the roadway, and in
many cases only pavement marking modifications are required to make the change. In other cases, the Road Diet may be planned in
conjunction with reconstruction or simple overlay projects, and the change in cross section allocation can be incorporated at no additional
Geometric and operational design features should be considered during the design of a Road Diet. Intersection turn lanes, traffic volume,
signing, pavement markings, driveway density, transit routes and stops, and pedestrian and bicyclist facilities should be carefully
considered and appropriately applied during the reconfiguration for appropriate Road Diet implementation. As with any roadway treatment,
determining whether a Road Diet is the most appropriate alternative in a given situation requires data analysis and engineering judgment.
Once installed, it is important to monitor the safety and operational effects of the corridor, and to make changes as necessary to maintain
acceptable traffic flow and safety performance for all road users. Evaluation of Road Diets will provide practitioners the information needed
to continue implementing reconfiguration projects in their jurisdictions.
Hosted by the FHWA, the Alabama Local Technical Assistance Center Program and the Alabama Department of Transportation at these locations: Central Office, Conference Room 8
1409 Coliseum Boulevard
Montgomery, AL 36130-3050
North Region-Guntersville Area
(Previously 1st Division), Auditorium
23445 Highway 431 North, Guntersville, AL
Second Division
295 Highway 20, East
Tuscumbia, AL 35674
Southwest Region-Mobile
1701 North Beltline Highway
Mobile, Alabama 36618
Two Perimeter Park South, Suite 500 East,
Birmingham, AL 35243; (205) 940-6420
Register online:‐education/online‐orders.html PLEASE CONTACT LARRY SELLERS or GARRY HAVRON WITH ANY QUESTIONS: Office 334‐844‐4370; Direct Line 334‐844‐5714; Toll‐free 800‐446‐0382