A typical road diet technique is to reduce the number of lanes on a roadway cross-section. One of the most common applications of a road diet is to improve safety in the context of two-way streets with 4-lane sections. In this case, two travel lanes in each direction are converted into a 3-lane section with one travel lane in each direction, optional bicycle lanes, and a two-way turn lane in the middle. The two-way turn lane can be transitioned into dedicated left turn lanes at intersections. The additional space that is freed up by removing a vehicular travel lane can be converted into bicycle lanes on either side of the roadway. Road diets are usually successful on roads carrying fewer than 19,000 vehicles per day. If properly designed, traffic does not divert to other streets after a road diet has been installed. In fact road diets have been found to maintain (and enhance) traffic flow while reducing crashes.
Vehicular speeding is a major concern citywide. In the past two years, 20 percent of the traffic collisions in the City were related to unsafe speed. In 2009, the City Council adopted a Strategic Plan goal that called for the City to adopt a speed management program. To achieve that goal, a study of best practices in speed management was commissioned by the City. That study indicated that narrowing streets (via road diets) and providing speed feedback to motorists to promote self-compliance with speed limits are the most successful approaches to managing speed on major streets. To that end, the Department of Transportation developed a speed management program and included it in the FY 2011-2016 Capital Improvement Program. The speed management program will install speed feedback signs and implement road diets on appropriate street segments as part of the annual pavement maintenance program.
3) How can a road with fewer lanes carry the same amount of traffic?
When a car stops in a moving traffic lane to turn left it causes congestion, blind spots, unsafe lane changes, and changes in vehicle speeds. In a three-lane system there is always one lane for driving, and one lane for turning making driving safer and more reliable, with fewer crashes and frustrations. For these reasons, a 3-lane road can handle the same amount of traffic as a 4-lane road (and in some cases it can handle more traffic).
As mentioned above, road diets provide a center turn lane so that left turns are simpler. A driver crosses only one lane of traffic at a time resulting in fewer blind spots. With an undivided four lane road, a driver must find a gap in two or three lanes of traffic at once to make a left turn.
First, you only have to cross three lanes of traffic, not four. Second there are fewer blind spots as you only have one lane in each direction, thus there is less sight blockage by cars. Third top vehicle speeds in a three lane system are lower.
The installation of bike lanes significantly increases safety for cyclists. Without bike lanes a cyclist is at risk of being 'doored' by someone getting out of a parked car, or being 'mirrored' by a motor vehicle passing by within a foot or two.
Cordova Street is an ideal candidate for a road diet within the City of Pasadena. It has a variable roadway width of 56 to 60 feet with minimum 10 foot sidewalks and carries less than 11,000 total car trips per day. Traffic volumes on Cordova have been stable for many years. Cordova Street is adjacent to portions of the Central District that have become more mixed-use over time with a variety of residential, commercial, and institutional land-uses. As the area has become more mixed use, Cordova Street has seen an increase in pedestrian and bicycle activity and an increase in conflicts between pedestrians, bicycles and motor vehicles. Narrowing the travel way on Cordova Street with a road diet can improve safety for all users of the street, while maintaining on-street parking and reasonable conditions for vehicles traveling on the street. The proposed project will convert the vehicular-oriented street to a complete street by removing two vehicular traffic lanes to accommodate bicycle facilities and to improve pedestrian crossings of Cordova Street. The proposed street configuration will consist of curb extensions to shorten pedestrian crossing times at all intersections, bike lanes in each direction, a painted two-way turn lane and one lane of traffic in each direction. Driveways do exist along Cordova Street; however, the two-way turn lane will provide a safer environment for motorists, cyclists and pedestrians as it allows the motorist the opportunity to wait out of the travel lane and observe cyclists and pedestrians before entering the driveways from Cordova Street. This project will also provide for bicycle detection systems at all intersections controlled by traffic signals along the project segment. The bicycle detection will be tied into the City of Pasadena’s Traffic Management Center to allow for the identification of traffic congestion and enhanced traffic operations support for the corridor. Existing and Proposed Cross Sections on Cordova Street Typical New Striping at Intersections
Highway Safety Information System (HSIS) – Evaluation of Lane Reduction “Road Diet” Measures on Crashes
• Institute of Transportation Engineers Road Diet Handbook • Walkable Communities- Road Diet Fixing the Big Roads