Common Road Diet Configurations
The most common type of road diet converts an undivided four lane roadway with two travel lanes on each side to an undivided three-lane roadway with one travel lane on each side and a center two-way left-turn lane.
This type of road diet allows space to be reallocated for other uses such as bike lanes, pedestrian refuge islands, transit uses, and/or parking.
A common misconception is that reducing the number of through lanes by installing a Road Diet will cause traffic to become more congested. In many cases, road diets can maintain traffic capacity on roadways like Main Street/Route 28. If a roadway contains many access points and driveways, most through-traffic uses the outside lanes to avoid being delayed by left-turning vehicles that frequently slow and stop in the inside lanes. Four-lane corridors often operate like three-lane roads with one through lane in each direction, so when they are converted to a three-lane section they are unlikely to experience a change in capacity.
Often, signalized intersections are the most significant constraint on roadway capacity. Road diets can reduce travel delays at intersections that experience large numbers of turning vehicles. Converting four through-lanes to two through-lanes makes it possible to install dedicated turn lanes at several intersections on Main Street.
- Road diets have shown to reduce overall crash rates by 19 to 47 percent
- Dedicated left-turn lanes reduce rear-end and left-turn crashes
- Fewer conflict points along the roadway and at intersections reduce crash risk
- Fewer lanes can reduce speeds by eliminating passing
- Lowers speeds and fatal and injury crash rates
Safer Accommodations for Vulnerable Users
- Reduced pedestrian and bicycle crash risk
- Increased space between travel lanes and sidewalks
- Fewer travel lanes for pedestrians to cross
- Can reallocate space for dedicated bicycle facilities, wider sidewalks, or other desirable amenities
- Separate left-turns at signalized intersections allow for more consistent traffic flow
- Can be incorporated into the repaving schedule
Proven Results in Massachusetts
Summer Street Road Diet Pilot in Hingham
- Speeds decreased as much as 5 mph
- Little to no travel time increase
- Little to no traffic diversion
Route 135 in Wellesley
- 55% fewer crashes
- 69% fewer severe injury occurrences
Nonantum Road in Boston, Newton, and Watertown
- 23% fewer crashes
- 32% fewer severe injury occurrences
Road Diet Resources from Federal Highway Administration
Resources and information about Road Diets.