Road diet

A road diet, also called a lane reduction or road rechannelization, is a technique in transportation planning whereby the number of travel lanes and/or effective width of the road is reduced in order to achieve systemic improvements.

Techniques

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 or provide space for other modes of travel. For example, a two-way, four lane road might be reduced to one travel lane in each direction. The freed-up space is then used to provide or enhance some of the following features:

• Adding or widening of footpaths/sidewalks
• Adding or widening of boulevards (landscaping strips)
• Adding cycle lanes on one or both sides of the road
• Widening remaining traffic lanes (if previously unsafely narrow to allow four lanes)
• Adding a center turn lane / flush traffic median for turning traffic
• Adding a reversible center lane
• Conversion of the rightmost or leftmost travel lane to a breakdown lane (The Lodge Freeway in metro Detroit is an example of this after I-96, the Jeffries freeway was built.)

If properly designed, traffic does not divert to other streets after a road diet, because the road previously provided excessive capacity. In other scenarios, reduction of traffic (either local traffic or overall traffic) are intended in the scheme. Road diets are usually successful on roads carrying fewer than 19,000 vehicles per day. Road diets can succeed at volumes up to about 23,000 vehicles per day. However, more extensive reconstruction is needed. Examples include replacing signals with roundabouts, traffic calming on parallel streets to discourage traffic from diverting away from the main road, and other means to keep traffic moving smoothly and uniformly.

Lane diets

In a lane diet, the width of a lane is decreased to reduce vehicle speeds and yield space for other use. Typically vehicular travel lane widths are narrowed to no more than ten feet, and left turn (in countries where drivers use the right-hand side of the road) storage lanes to nine or ten feet. Resulting space can be applied to pedestrian refuges, medians, sidewalks, shoulders, parking, or bike lanes. Lane width guidelines in the United States are offered as a range and lane diets fall within this range.

Benefits

Proponents of road diets generally believe key benefits include lower vehicular speeds, reduced crash rates, and improved pedestrian safety. Other benefits of road diets include promoting better land use, reducing induced traffic, promoting greater driving attentiveness, and promoting cycling through the addition of bicycle lanes. Providing dedicated left turn (in countries that drive on the right-hand side of the road) lanes at intersections can improve vehicular safety and can enable efficiency gains along the roadway.

Researchers have found that road diets can be expected to reduce overall crash frequency by 19% to 43%, with the higher crash reductions occurring in small urban areas than in metropolitan areas.^[1]

A leading proponent of road diets is former Florida Bicycle and Pedestrian Coordinator Dan Burden, who now helms the Walkable and Livable Communities Institute. Burden and Peter Lagerwey published an article on the topic in 1999^[2] noting that in two cases, 95% of residents were initially opposed to roadway constriction. Additional studies have shown that road diets often achieve these positive effects without reducing traffic volumes.

Among studies now showing that there are safety improvements to driving when lane widths are reduced include a recent report by the National Cooperative Highway Research Program (NCHRP) and work analyzing traffic safety for 14 years in all 50 states by Robert B. Noland.^{[citation needed]}

Criticisms

Road diets can negatively affect the speed and reliability of transit service operating on the roadway, particularly if bus stops are located in pullouts and traffic queues delay buses attempting to re-enter traffic. Constructing bus bulbs can mitigate these effects though this feature results in delays for other vehicles.

Not all multi-lane arterials are good candidates for road constriction. Added congestion can outweigh benefits if vehicle traffic volumes exceed the capacity of the three-lane roadway. This threshold is approximately 20,000 vehicles per day.^[3] Burden notes additional characteristics of better candidates for vehicle lane removal.

Implementations

United States

There are perhaps over 20,000 road diets in the United States, with another 500-1,000 being conducted each year.^{[citation needed]}

The city in North America with the greatest number of road diets (over 50) is San Francisco, with 4 to 6 road diets added each year. The city with the greatest number of road diets, per capita, is Hartford, Connecticut (12). Retail merchants in Seattle are now some of the strongest proponents for these projects, since reduced travel speeds allow for easier and safer parking, improve store access and boost overall walking and liveability conditions in neighbourhoods, all of which lead to improved commerce.^{[citation needed]}

Palo Alto, California has studied reducing the number of vehicle travel lanes to reduce traffic impacts on some of its busiest streets since adopting a new Comprehensive Plan in 1998. Design plans were made to reduce the total number of travel lanes from four to two on Embarcadero Road and Middlefield Road in the early 2000s, but were never brought to the city council for approval. Lane reductions were approved and then implemented on Charleston Road in 2006,^[4] Arastadero Road in 2010,^[5] and Deer Creek Road in 2011.^[6]

The city of Seattle has implemented Road Diets over the past few years, and was able to boost its ranking from 6th to 2nd highest traffic rates in the US.^{[citation needed]}

References

See also

• Reversible lane
• Contraflow lane reversal
• 2+1 road

External links

• Project for Public Spaces: Rightsizing Streets Guide
• Summary Report: Evaluation of Lane Reduction "Road Diet" Measures and Their Effects on Crashes and Injuries
• Applying the Road Diet for Livable Communities (2005 slide presentation with photos)
• The Safety and Operational Effects of "Road Diet" Conversions in Minnesota (2007)
• Streetscape Improvements: Enhancing Urban Roadway Design (updated 2007)
• Road Space Reallocation Roadway Design and Management To Support Transportation Alternatives (updated 2007)
• Interview with Dan Burden (2005)
• Seattle's Stone Way Report (2010)
• Walkable 101: Road Diets
• StreetFilms: Road Diet