Road diet
Encyclopedia
A road diet, also called a lane reduction, is a technique in transportation planning
whereby a road is reduced in number of travel lanes and/or effective width in order to achieve systemic improvements.
If properly designed, traffic does not divert to other streets road 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 roundabout
s, 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.
. 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 overal crash frequency by 19% to 43%, with the higher crash reductions occurring in small urban areas than in metropolitan areas. .
A leading proponent of road diets is professional lobbyist and former Florida Bicycle and Pedestrian Coordinator Dan Burden; Burden and Pete Lagerwey published a definitive article on the topic in 1999. This article notes 95% of residents were initially opposed to roadway constriction. Additional studies have since been published, showing that road diets achieve these positive effects—often 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 Safety Research Program (NCHRP) and work analyzing traffic safety for 14 years in all 50 states by Robert B. Noland.
Road diets can negatively affect the speed and reliability of transit service operating on the roadway, particularly if bus stop
s are located in pullouts and traffic queues delay buses attempting to re-enter traffic. Constructing bus bulb
s 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. Burden notes additional characteristics of better candidates for vehicle lane removal.
The city in North America with the greatest number of road diets (at least 38) is San Francisco. The city with the greatest number of road diets, per capita, is Hartford, Connecticut (12). One or two new road diets are added to each of these cities annually. 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 livability conditions in neighborhoods ... all of which leads to improved commerce.
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 Rd and Middlefield Rd in the early 2000s, but were never brought to the city council for approval. Lane reductions were approved and then implemented on Charleston Rd in 2006 and Arastadero Rd in 2010, and Deer Creek Rd in 2011.
Transportation planning
Transportation planning is a field involved with the evaluation, assessment, design and siting of transportation facilities .-Models and Sustainability :...
whereby a road is reduced in number of travel lanes and/or effective width 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 users in the context of two-way streets with 2 lanes in each direction. The road diet reduces this to 1 travel lane in each direction. The freed-up space is then used to provide any or several of the following features:- (Wider) footpaths/sidewalkSidewalkA sidewalk, or pavement, footpath, footway, and sometimes platform, is a path along the side of a road. A sidewalk may accommodate moderate changes in grade and is normally separated from the vehicular section by a curb...
s - (Wider) landscaping strips
- Cycle lanes, on one or both sides of the road
- Wider lane widths on remaining traffic lanes (if previously unsafely narrow to allow four lanes)
- A two-way turn lane / flush traffic median for turning traffic
- A reversible centre laneReversible laneA reversible lane , called a counterflow lane or contraflow lane in transport engineering nomenclature, is a lane in which traffic may travel in either direction, depending on certain conditions...
If properly designed, traffic does not divert to other streets road 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 roundabout
Roundabout
A roundabout is the name for a road junction in which traffic moves in one direction around a central island. The word dates from the early 20th century. Roundabouts are common in many countries around the world...
s, traffic calming
Traffic calming
Traffic calming is intended to slow or reduce motor-vehicle traffic in order to improve the living conditions for residents as well as to improve safety for pedestrians and cyclists. Urban planners and traffic engineers have many strategies for 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. National lane width guidelines are offered as a range (within the United States), and lane diets fall within this range.Arguments for and against
Proponents of road diets generally believe key benefits include lower vehicular speeds, reduced crash rates, and improved pedestrian safetyPedestrian
A pedestrian is a person traveling on foot, whether walking or running. In some communities, those traveling using roller skates or skateboards are also considered to be pedestrians. In modern times, the term mostly refers to someone walking on a road or footpath, but this was not the case...
. Other benefits of road diets include promoting better land use, reducing induced traffic, promoting greater driving attentiveness, and promoting cycling
Cycling
Cycling, also called bicycling or biking, is the use of bicycles for transport, recreation, or for sport. Persons engaged in cycling are cyclists or bicyclists...
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 overal crash frequency by 19% to 43%, with the higher crash reductions occurring in small urban areas than in metropolitan areas. .
A leading proponent of road diets is professional lobbyist and former Florida Bicycle and Pedestrian Coordinator Dan Burden; Burden and Pete Lagerwey published a definitive article on the topic in 1999. This article notes 95% of residents were initially opposed to roadway constriction. Additional studies have since been published, showing that road diets achieve these positive effects—often 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 Safety Research Program (NCHRP) and work analyzing traffic safety for 14 years in all 50 states by Robert B. Noland.
Road diets can negatively affect the speed and reliability of transit service operating on the roadway, particularly if bus stop
Bus stop
A bus stop is a designated place where buses stop for passengers to board or leave a bus. These are normally positioned on the highway and are distinct from off-highway facilities such as bus stations. The construction of bus stops tends to reflect the level of usage...
s are located in pullouts and traffic queues delay buses attempting to re-enter traffic. Constructing bus bulb
Bus bulb
A bus bulb, also called a bus boarder or bus border, is an arrangement by which a sidewalk is extended outwards for a bus stop; typically the bus bulb replaces roadway that would otherwise be part of a parking lane...
s 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. Burden notes additional characteristics of better candidates for vehicle lane removal.
United States
There are perhaps over 20,000 road diets in the United States, with another 500-1,000 being conducted each year.The city in North America with the greatest number of road diets (at least 38) is San Francisco. The city with the greatest number of road diets, per capita, is Hartford, Connecticut (12). One or two new road diets are added to each of these cities annually. 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 livability conditions in neighborhoods ... all of which leads to improved commerce.
Palo Alto, California
Palo Alto, California
Palo Alto is a California charter city located in the northwest corner of Santa Clara County, in the San Francisco Bay Area of California, United States. The city shares its borders with East Palo Alto, Mountain View, Los Altos, Los Altos Hills, Stanford, Portola Valley, and Menlo Park. It is...
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 Rd and Middlefield Rd in the early 2000s, but were never brought to the city council for approval. Lane reductions were approved and then implemented on Charleston Rd in 2006 and Arastadero Rd in 2010, and Deer Creek Rd in 2011.
External links
- Dan Burden's article on road diets
- 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)