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Selecting a Road Diet Location

Jan 31, 2020
Jan 30, 2020

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Is Your Street Right for a Road Diet? 

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Streets should be evaluated to determine whether or not rightsizing is a good fit, and if so, what types of solutions would be most effective. Once selected to be rightsized, measures of success should be immediately implemented that can help build support for this initiative and other similar efforts in the future. Our guide to measuring impact can help with that. 

How do you decide which streets to prioritize for rightsizing strategies? It’s important for each community to determine its own criteria, which should reflect the realities of its streets and the people who use them. Here are a few factors to consider, which were informed by conversations with professional planners who have worked on these projects across the country.

  • Community Priorities 
  • Street Typology and Traffic Volumes 
  • Street Safety 
  • Land Use 
  • Jurisdiction and Budget Allocation

Community Priorities 

The most successful rightsizing projects are those that are desired by a community, and that reflect their vision and values for the street. Indications of a community’s vision for a street and its surrounding area are often articulated in a master or community plan, which could include such goals as improving safety, walkability, bikeability, street life, and/or main street retail. 

Streets that would provide important pedestrian and bicycle connections in a community, as indicated by a bicycle or pedestrian master plan, could also be good candidates for rightsizing. Residents or businesses may clash with the state or local transportation department in charge of their street. Community members and such departments may differ in their assessment of a street’s suitability for rightsizing. Compromise is often possible through a lighter, quicker, cheaper trial implementation, using inexpensive paint and temporary bollards to try out the proposed configuration prior to committing with hard infrastructure.

Street Typology and Traffic Volumes

Reducing the space available for motor vehicles will be more difficult if the street is a major thoroughfare for freight movement or has high vehicle volumes. For example, transportation practitioners interviewed for this project said that they typically do not promote rightsizing projects for streets with more than 20,000-25,000 average daily vehicles without exceptional circumstances and evaluation, and that streets with more than 15,000 average daily vehicles often demand an operational analysis to look closely at impacts before implementing a four-to-three-lane conversion.

Conversely, a street with a low number of daily vehicles is often a more suitable candidate for rightsizing. A street with 7,000 to 15,000 daily vehicles can generally handle a four-to-three lane conversion with no adverse impact on travel times or flow whatsoever, and may be pursued with relatively little study.

However, broader goals for the street should often supersede concerns about impacting traffic volumes. If there are parallel roads that are acceptable to divert traffic, and the community wants a more pedestrian-oriented street, rightsizing may be a useful option regardless of the number of daily vehicles.
The physical layout of the street must also be suitable for the changes proposed. For instance, streets with short distances between intersections, especially when they have high traffic volumes, are more difficult to remove movement lanes from without risking negative congestion. Frequency of driveways, bus stops, and space at intersections can create challenges to implementation.

Further, intersections should allow turning movements for larger vehicles like emergency vehicles, buses and trucks, where necessary. Emergency vehicles can sometimes improve their travel times where there is a two-way left turn lane, if there is no raised median, because they can easily gain exclusive access to the center lane to create a passing lane. However, some cities around North America are learning from their European counterparts by adopting smaller emergency vehicles in part to allow for more flexible, human-centered street design.

Implementing organizations may need to run traffic simulations of their proposed street changes to predict their functionality and evaluate potential turning, regulation, or signal time adjustments. Few street geometry issues will preclude the possibility of rightsizing, but rather suggest the need for careful analysis and implementation.

Street Safety 

Streets with high levels of traffic collisions, particularly involving pedestrians and bicyclists, are excellent candidates for rightsizing projects. Sideswipe, rear-end, and head-on crashes during turns against traffic are particularly likely to be mitigated by converting through-lanes to a two-way left turn lane. Further, crash frequency and severity will be reduced when vehicle speeds are slower.

Land Use 

Adjacent land uses help indicate the appropriateness of a street for rightsizing. Land uses that generate high numbers of pedestrians and bicyclists, such as college campuses, schools, parks, and local retail, typically suggest that a street would benefit from rightsizing improvements.

Jurisdiction and Cost 

Sometimes one jurisdiction, like a municipality, is interested in implementing a rightsizing project while another jurisdiction, like a state, is not. Depending on the road, it may be possible to transfer the right-of-way to the willing jurisdiction, as happened with Edgewater Drive in Orlando Florida, which changed hands from the State of Florida to the City of Orlando.

Of course, cost influences what kind of redesign is possible on a street as well. An agency may prioritize rightsizing projects on streets that are already scheduled for repaving or restriping, which can reduce the cost of changes and create the impetus for a conversation about the street's future. The cost of creating hard infrastructure, like neckdowns, can raise project costs considerably compared to simply changing the street’s striping. However, dangerous or poorly functioning streets also have significant societal and health costs that must be considered when evaluating the possibility of rightsizing a street.

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