Milly Gaines
A road diet is a transportation planning technique that reduces the number and/or width of lanes on a road. The aim is to improve safety, reduce crashes, and provide space for other travel modes such as bike lanes, sidewalks, and public transit. By removing or repurposing lanes, road diets can calm traffic, reduce vehicle miles travelled, and cut emissions. They are typically implemented on roads with fewer than 20,000 vehicles per day, and have been shown to be successful in cities like Seattle, San Francisco, and New York. While road diets are a low-cost solution, they can be controversial due to concerns about increased congestion and resistance to changes in street parking and driving lanes.
| Characteristics | Values |
|---|---|
| Definition | A technique in transportation planning that reduces the number and/or width of lanes on a road |
| Purpose | To improve safety, cut emissions, calm traffic, and enhance livability |
| Common Types | "Three lanes to two," "four lanes to three," "bike lanes to cycle tracks," and "40-footer lane insertion" |
| Techniques | Lane reduction, road rechannelization, or road conversion |
| Benefits | Reduced crashes, deaths, and injuries; improved safety for pedestrians, cyclists, and vulnerable road users; enhanced mobility and access; encouraged multimodal travel; reduced vehicle miles travelled (VMT) and GHG emissions; improved traffic flow; reduced congestion; increased business; and lower costs |
| Drawbacks | Potential for increased congestion and diversion of traffic to alternate routes if average daily traffic exceeds 20,000 vehicles; negative impact on emergency response times; opposition from community groups due to loss of parking spaces and increased property values |
| Implementation | Typically applied to roads with 8,000 to 25,000 daily vehicle traffic; can be implemented at a low cost, often for the price of restriping |
| Examples | Valencia Street in San Francisco, Luten Avenue in Staten Island, Nickerson Street in Seattle, Stone Way in Seattle, East 14th Street in San Leandro, Ocean Park Blvd in Santa Monica |
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What You'll Learn
Road diet implementation
Road diets, also known as roadway reconfiguration, are a proven safety countermeasure that has been implemented by transportation agencies for over three decades. They are typically applied to four-lane undivided highways, which experience high crash frequencies due to conflicts between high-speed traffic, turning vehicles, and other road users. The primary benefits of road diets include enhanced safety, mobility, and access for all road users, as well as the creation of complete streets that accommodate various transportation modes.
A classic road diet involves converting a four-lane undivided roadway into a three-lane segment with two through lanes and a center, two-way left-turn lane. This simple reconfiguration can lead to a significant reduction in crashes, ranging from 19 to 47%, or even up to 52% according to FHA studies. Additionally, it reduces vehicle speed differentials, improves mobility, and maintains the volume of people who can move along the roadway.
When considering road diet implementation, several factors come into play:
- Candidate locations: Road diets are typically implemented on roadways with a current and future average daily traffic of 25,000 or less. They are applied to streets with excess capacity to avoid creating congestion.
- Capacity constraints: Understanding the level of service, quality of service, average daily traffic, peak hours, turning volumes, and patterns are crucial when planning a road diet.
- Public outreach and response: Gaining public acceptance and support from elected officials is essential to overcoming opposition.
- Evaluation metrics: Before-and-after studies, observational studies, and surrogate measures of safety are used to evaluate the effectiveness of road diets.
- Slow-moving vehicles: Considerations for frequently stopping and slow-moving vehicles are important to maintain traffic flow.
- Cost and funding: Road diets can be implemented at a low cost, especially when planned with simple pavement overlay projects, as the reconfiguration can be achieved through restriping.
The Federal Highway Administration (FHWA) offers free workshops and technical assistance to support Road Diet implementation. They also provide guidance and informational resources on various aspects of road diet planning, including data needs, vehicle and non-motorized operations, design controls, intersection design, and more.
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Road diet benefits
Road diets are a low-cost solution to improve safety and enhance mobility for all road users. They are typically implemented on roadways with an average daily traffic volume of 25,000 vehicles or fewer. The primary benefit of a road diet is enhanced safety, achieved through a reduction in vehicle speeds and crashes. By converting a four-lane road into three lanes, with one lane in each direction and a shared centre turn lane, the risk of collisions and serious injuries is significantly decreased. This is especially beneficial for older and inexperienced drivers, who are more prone to crashes. Additionally, the wider shoulders created by lane reductions provide a recovery area for drivers who depart from the road.
Road diets also provide increased space for alternative modes of transportation, such as walking, bicycling, and public transit. The space reclaimed from lane reductions can be used for turn lanes, bus lanes, pedestrian refuge islands, bike lanes, sidewalks, bus shelters, parking, or landscaping. This encourages active transportation, supports the local economy, and creates a more livable and complete street environment.
Furthermore, road diets have been shown to reduce traffic congestion in certain areas. For example, in Seoul, South Korea, a road diet implementation resulted in a substantial easing of traffic congestion, leading to a 34% reduction in accidents. Additionally, the slower traffic speeds resulting from road diets can benefit local businesses as motorists are more likely to notice shops, eateries, and businesses along the roadway.
While road diets are controversial in some communities due to concerns about increased delays, studies have shown that they can achieve positive effects without reducing traffic volumes. When properly installed, road diets can decrease the risk of crashes and improve safety for all road users, making them a valuable tool for creating safer and more livable communities.
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Road diet controversies
Road diets are transportation planning techniques that reduce the number and/or width of lanes on a road. The aim is to improve safety, reduce emissions, and calm traffic. While road diets have been proven to achieve these goals, they are often controversial.
One of the main controversies surrounding road diets is the concern that reducing the number of lanes will lead to increased congestion. This worry has been raised by members of the public, local business owners, and political stakeholders. In some cases, such as in Playa del Rey, Los Angeles, residents have pushed back against road diet programs, leading to the restoration of lanes.
Another issue is the cost of implementing road diets. While they are meant to be cost-effective, road diets can sometimes require significant construction work, resulting in high costs for relatively minor improvements. For example, a road diet project in Anchorage, Alaska, took 20 years and incurred at least $10 million of debt for less than a mile of improvements.
Furthermore, road diets can be controversial because they may not always lead to a reduction in traffic collisions. A road diet is only effective when properly designed and implemented. If a road previously had excess capacity, reducing the number of lanes may not divert traffic to other streets. However, when average daily traffic exceeds 20,000 vehicles, safety improvements from a road diet may be offset by increased congestion and the diversion of traffic to alternate routes.
Despite these controversies, road diets have been successfully implemented in several cities across the United States, including San Francisco, New York, and Chicago. These projects often require strong political support and community outreach to overcome opposition.
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Road diet examples
A road diet is a technique in transportation planning that reduces the number and/or width of lanes on a road. This is often done to improve safety and reduce crash rates, as well as to provide space for other modes of travel such as bike lanes, bus lanes, and sidewalks. They are typically implemented on roadways with an average daily traffic of 25,000 or less and have been proven to reduce overall crash frequency by 19-47%.
- Seattle, Washington: In 2010, the city's department of transportation implemented a road diet on Nickerson Street, converting a four-lane road into a three-lane road with one lane in each direction and a shared centre turn lane. This resulted in improved pedestrian safety and a reduction in travel speeds, with collisions decreasing by 23% in the following year.
- San Francisco, California: San Francisco has completed the most road diet projects among American cities, with over 40 projects since the late 1970s. One notable example is Valencia Street, which was reduced from four to two travel lanes with a centre turn lane and bike lanes added in March 1999.
- London, UK: During the COVID-19 pandemic, London implemented several road diets to give more space to active travel modes such as bicycle lanes. One example is Park Lane, where the three-lane northbound carriageway was reduced to one lane for motor traffic, one bus lane, and one segregated cycle way.
- San Jose, California: San Jose has implemented several road diets since 2011 as part of its "Envision 2040" General Plan, which calls for road diets on streets with excess vehicle capacity to provide wider sidewalks, bicycle lanes, and landscaping.
- Old Georgetown Road, Montgomery County, Maryland: While a full report is not yet available, preliminary data indicates a reduction in car crashes since the implementation of a road diet on this road, which included the addition of controversial bike lanes.
- Woodward Ave, Ferndale, Michigan: This road is currently undergoing a road diet, with one lane on each side being turned into a protected bike lane and parking.
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![Traffic [Blu-ray]](https://m.media-amazon.com/images/I/81bSBV-V1tL._AC_UY218_.jpg)
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Road diet types
A road diet, also known as lane reduction, road rechannelization, or road conversion, is a technique in transportation planning that reduces the number and/or width of lanes on a road. This is often done to improve safety and reduce crash rates, calm traffic, and provide space for other modes of travel.
There are several types of road diets, depending on the number of lanes reduced and the specific configuration of the remaining lanes. Here are some common types:
- Four lanes to three lanes: This is one of the most common types of road diets, especially in urban and suburban areas. It involves converting a four-lane undivided roadway to three lanes, with two through lanes and a centre two-way left-turn lane. This configuration reduces crashes, improves safety for pedestrians and cyclists, and can accommodate enhancements such as bicycle lanes and on-street parking.
- Three lanes to two lanes: This type of road diet reduces a three-lane road to two lanes, typically one travel lane in each direction. This can be effective in locations with medium to high access densities, as it may not significantly impact traffic flow while providing the benefits of improved safety and reduced speeds.
- Bike lanes to cycle tracks: This type of road diet involves converting traditional bike lanes into protected cycle tracks or paths separated from vehicular traffic. This enhances the safety and comfort of cyclists, providing a dedicated space for bicycle travel.
- Lane width reduction: In this type of road diet, the width of vehicular travel lanes is reduced, typically to no more than 2.8 metres (9.1 feet). This helps to slow down traffic, reduce accidents, and create space for other uses, such as pedestrian zones, sidewalks, or bike lanes.
- 40-footer lane insertion: While specific details on this type of road diet are limited, it appears to involve inserting a 40-foot lane into the existing roadway configuration. This could be a dedicated lane for specific purposes, such as public transportation or bicycles.
It is important to note that the success of a road diet depends on proper planning and implementation. While road diets can improve safety and provide multiple benefits, they may also lead to increased congestion and diversion of traffic to alternate routes if not carefully designed and executed.
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Frequently asked questions
A road diet is a technique in transportation planning that reduces the number and/or width of lanes on a road. This is often done to improve safety, enhance mobility, and provide space for non-vehicle modes of transportation.
Road diets are implemented to improve safety, cut emissions, and calm traffic. They are also used to provide space for other modes of transportation such as bike lanes, bus lanes, sidewalks, and pedestrian zones.
The benefits of a road diet include a reduction in crashes, improved mobility and access for all road users, and a more complete streets environment that accommodates various transportation modes.
Successful road diet implementations include projects in Seattle, San Francisco, New York, Palo Alto, and London. For example, in 2010, Seattle's Nickerson Street implemented a road diet that improved pedestrian safety and reduced travel speeds.
One potential drawback of a road diet is increased congestion, especially when the average daily traffic exceeds 20,000 vehicles. Additionally, some communities may oppose road diets due to concerns about reduced traffic lanes and parking spaces, as well as increased property values and maintenance costs.
![Traffic [DVD]](https://m.media-amazon.com/images/I/91uK8hKaoDL._AC_UY218_.jpg)
