Road safety is paramount for everyone, whether they drive, bike, walk, or use public transport. Initially, roadway projects in the 1950s and 1960s primarily focused on expanding the system and capacity. A common solution to congestion on a two-lane road was to add more lanes, leading to the prevalence of four-lane roads across the country. However, four-lane, undivided roadways often function like two-lane roads with left-turn lanes, as drivers tend to avoid inside lanes due to potential delays caused by left-turning vehicles.
Understanding the Road Diet
A "road diet" involves reducing the number of vehicle travel lanes while maintaining the same road width. This lane reduction or reconfiguration typically converts a four-lane, undivided road into a two-lane road with a center, two-way left-turn lane (TWLTL). This reallocation of roadway space uses the same amount of pavement but rearranges the lane markings. By providing dedicated space for left-turning traffic and through traffic, only three lanes are needed instead of four.
Safety Benefits of Road Diets
The Federal Highway Administration (FHWA) has reported that four-lane, undivided roads have a history of high crash rates. Road diets offer significant benefits for roads with expected collisions and speeding or in sensitive areas near schools, parks, and neighborhoods, including an overall crash reduction rate of 19 to 47 percent. Fewer lanes also mean fewer lanes for side-street motorists to cross, reducing the rate of right-angle crashes.
Enhanced Pedestrian and Bicyclist Safety
Pedestrian safety increases exponentially with fewer lanes to cross. Dedicated bicyclist/pedestrian space also helps to increase driver awareness of other roadway users. Reallocation of space allows for designated bike lanes, on-street parking, pedestrian refuge islands, and transit stops.
Traffic Calming and Reduced Speeds
A road diet "calms" traffic and reduces vehicle speeds, which helps reduce crash risk and the severity of collisions. The turning gap selection for left turns is simplified, with only one lane of traffic to cross. This is especially important for inexperienced and older drivers, as these age groups experience higher rates of traffic crashes. Wider shoulders created by a lane reduction offer recovery space if a driver departs the road.
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Economic Vitality
Increased economic vitality often accompanies lane reduction projects, creating a destination for users. The primary benefit of a road diet is safety, as reducing the number of lanes minimizes the mixing of through traffic with turning traffic.
Feasibility and Considerations
While road diets increase safety and help foster a cohesive transportation network, they aren’t appropriate or feasible in all instances. A road diet isn’t an automatic, one-size-fits-all solution. Many factors, from the number of driveways and intersections in a corridor to right-of-way availability and cost, must be considered before moving forward with a road diet. Understanding your community's goals for improvement is helpful when evaluating a corridor. Determining road diet feasibility begins by looking at the existing traffic volume and crash history of the corridor.
Cost-Effectiveness and Funding
As funding for roadway projects becomes increasingly limited, the desire for cost-effective, intelligent solutions is stronger than ever. The primary expense associated with road diets is road signage, lane markings, or signal modifications, making them relatively inexpensive. They can be planned in conjunction with other maintenance efforts, like resurfacing, and occur within the existing roadway footprint, which may reduce or eliminate costs associated with large reconstruction projects. Federal funding for road diets includes the Surface Transportation Program or Block Grant (STP/STBG) and the Highway Safety Improvement Program (HSIP). Where crash data support the expenditure, other state-level DOT traffic safety programs may also provide funding.
Cost and Speed Reduction Estimates
Road diet restriping is estimated to cost $25,000-$40,000, with geometric features increasing the cost significantly. Optical markings are low-cost and easy to install, but actual costs vary. Road diets have been shown to reduce speeds by 4-9%, while optical markings can reduce speeds by 0-27%. These estimates are based on past projects and commonly used materials and may vary depending on roadway condition, location, time, and other factors.
Return on Investment
When considering cost, it is helpful to keep in mind the potential return on investment in terms of enhanced safety. A study of rural highways in Kansas showed that edge lines would yield benefits exceeding their costs if an average of one non-intersection crash occurs annually every 15.5 miles of roadway.
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Speed Reduction Benefits
Road diets and marking measures have been found to effectively reduce the speed most people drive on a road. In one analysis, lateral shifts were found to reduce the 85th percentile speed by 25 percent on rural roads. The benefits of adding a centerline, in combination with existing edge lines, include low cost, flexibility, and ease of implementation. These measures can also offer additional safety benefits and flexibility in terms of implementation.
Case Studies
A pilot road diet was implemented in Hingham, MA, using flexible plastic delineator posts due to concerns around permanent lane elimination. Upon discovering speeds reduced as much as 5mph during the pilot, the town decided to implement a permanent road diet. After the pilot, it was also found that traffic and congestion was not increased as anticipated, contributing to their decision to make the road diet a permanent fixture.
Previous studies on centerlines have shown them to reduce crash frequency by 27 percent, and an FHWA Road Diet Study in Iowa found a 25 percent reduction in crashes per mile of roadway associated with a road diet and a 19 percent reduction in the overall crash rate. In one city, converting four general travel lanes to two-and adding a turn-lane-was found to have prevented 525 crashes on three streets.
Implementation Guidelines
When considering road diets and marking measures, it’s important to keep in mind the MassDOT Project Development Guidelines (Chapter 16). A road diet is a conversion of usually a four-lane roadway to a three-lane road made up of two through lanes and a center-two-way-left-turn -lane. Drivers can use the dedicated turn lane to safely turn and move out of the traffic flow, so they're not holding up drivers behind them. With a road diet, left turns will only cross one lane of traffic instead of two.
Lake Boone Trail Safety Improvement Project
The Lake Boone Trail between Ridge Road and the I-440 ramps is being enhanced with a major component of lane reconfiguration. Currently a four-lane road, Lake Boone Trail tends to have more crashes because of conflicts with turning traffic. Converting the road (from Ridge Road to I-440 ramps) to a three-lane roadway with a center turn lane decreases points of conflict between vehicles and prevents drivers from blocking travel lanes. The road diet allows for the addition of bike lanes along the corridor and a pedestrian refuge island, allowing safer connectivity to transit and the greenway trail along the street.
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Benefits for All Road Users
Road Diets have the potential to improve safety, convenience, and quality of life for all road users. For roads with appropriate traffic volumes, there is strong research support for achieving safety benefits through converting four-lane undivided roads to three-lane cross sections with TWLTLs. Operational and design changes associated with Road Diets that promote safety include reduced vehicle speeds, reduced vehicle-pedestrian, -bicycle, and -vehicle conflicts. Road Diets reduce vehicle-to-vehicle conflicts that contribute to rear-end, left-turn, and sideswipe crashes by removing the four-lane undivided inside lanes serving both through and turning traffic.
Reducing Speed Differential
Road Diets improve safety by reducing the speed differential. On a four-lane undivided road, vehicle speeds can vary between travel lanes, and drivers frequently slow or change lanes due to slower or stopped vehicles (e.g., vehicles stopped in the left lane waiting to turn left). Drivers may also weave in and out of the traffic lanes at high speeds. In contrast, on three-lane roads with TWLTLs the vehicle speed differential is limited by the speed of the lead vehicle in the through lane, and through vehicles are separated from left-turning vehicles. Thus, Road Diets can reduce the vehicle speed differential and vehicle interactions, which can reduce the number and severity of vehicle-to-vehicle crashes.
Benefits for Non-Motorized Road Users
Road Diets can be of particular benefit to nonmotorized road users. They reallocate space from travel lanes- space that is often converted to bike lanes or in some cases sidewalks, where these facilities were lacking previously. These new facilities have a tremendous impact on the mobility and safety of bicyclists and pedestrians as they fill in a gap in the existing network. Even the most basic Road Diet has benefits for pedestrians and bicyclists, regardless of whether specific facilities are provided for these modes. The speed reductions that are associated with Road Diets lead to fewer and less severe crashes. Uncontrolled and midblock pedestrian crossing locations tend to experience higher vehicle travel speeds, contributing to increased injury and fatality rates when pedestrian crashes occur. Midblock crossing locations account for more than 70 percent of pedestrian fatalities. A reduction in pedestrian crash risk was found when crossing two- and three-lane roads compared to roads with four or more lanes.
Pedestrian Refuge Islands
With the addition of a pedestrian refuge island - a raised island placed on a street to separate crossing pedestrians from motor vehicles - the crossing becomes shorter and less complicated. Pedestrians only have to be concerned with one direction of travel at a time. Road Diets often include either on–street parking or a bike lane, which create a buffer between pedestrians and moving vehicles. For bicyclists, the biggest benefit of Road Diets is through the addition of bicycle facilities. A Road Diet can transform a street that was formerly difficult for a bicyclist to travel along to a comfortable route that attracts many more bicyclists. When bicycle lanes are striped, bicyclists are more visible and motorists know where to look for them, speeds are reduced, and bicycle safety can be improved. Even without a dedicated bicycle lane or buffer, a motorist on a three-lane roadway is able to move over closer to the center lane on a three-lane roadway when approaching a bicycle.
Synergies Between Improvements
Added to the direct safety benefits, a Road Diet can improve the quality of life in the corridor through a combination of bicycle lanes, pedestrian improvements, and reduced speed differential, which can improve the comfort level for all users. Interviews with agencies that have implemented Road Diets found many synergies between improvements for one mode and their impacts on another. The City of Chicago found that the addition of pedestrian refuge islands was a significant benefit of their Road Diets. Some of the treatments for one mode have obvious synergies with other modes, such as bicycle lanes that not only provide added comfort for bicyclists, but also for pedestrians by increasing their separation from vehicles.
Potential Concerns and Mitigation
Road Diets can also introduce some traffic safety concerns. One concern is the use by pedestrians of TWLTLs as a refuge, which could make pedestrians vulnerable to being struck by vehicles traveling in the TWLTL. Some impacts are seen as a positive by some agencies and a negative by others, which may be dependent on the context and users of the roadway. In Iowa, a Road Diet along a truck route narrowed lanes from 13 feet to 10 feet; these seemed too narrow to commercial vehicle drivers. Meanwhile, in Chicago and Michigan, shoulders and buffers between bicycle lanes and travel lanes were added primarily to keep travel lanes to 12 feet wide or less. In addition, a common concern in implementing Road Diets is that drivers on cross-streets or driveways may have difficulty finding a suitable gap in traffic to enter the main roadway because through traffic is now using a single through lane.
Maintenance Funding
In some States maintenance funding can be affected. Lane-miles are sometimes used as the measurement to calculate budgets for maintenance activities, defined only as those miles used for motor vehicle traffic - not bicycle lanes, parking, or other uses. When a Road Diet is introduced, one-quarter of the motor vehicle lane-miles are removed, which can equate to a similar reduction in maintenance funds.
Community-Driven Road Diets
Most drivers base their travel speed on what feels comfortable given the street design. To protect both pedestrians and drivers many communities are putting their roads on "diets" by reducing street widths and vehicle lanes. The most common road diet involves converting an undivided four-lane road into three vehicle lanes (one lane in each direction and a center two-way left-turn lane).
Examples of Successful Road Diets
After narrowing a 1.5-mile section of Edgewater Drive in the College Park neighborhood of Orlando, vehicle crashes decreased by 34 percent and related injuries declined by 68 percent. After a road diet was completed on a 1.2-mile section of Seattle's Stone Way North, crash data showed an overall decrease of 14 percent, injury crashes dropped by 33 percent and angle crashes dropped by 56 percent. Bicycle volume increased 35 percent yet the bicycle crash rate showed no increase.
Road Diets in Kansas City, Missouri
A road diet, or reducing travel lanes for vehicles on a roadway, is a cost-effective solution to increase safety for vehicles, pedestrians, bicyclists and other roadway users. It’s a trend that’s sweeping the nation, and in 2014 the City Council passed a resolution directing the Public Works Department to analyze local road diet possibilities. The first road diet completed was Leeds Trafficway from Stadium Drive to Emanual Cleaver II Boulevard, which was repaved and restriped in 2015. Other road diets finished or underway since then are: E. Gregory Boulevard from Oldham Road to Cleveland Avenue; N.E. 108th Street from Smalley Avenue to Cookingham Drive; and N.E. Barry Road from Kenwood Avenue to Highland Avenue. The most recent road diet can be seen along Grand Boulevard. This road diet includes new bike lanes on each side of Grand, from 5th Street to 20th Street.
Identifying Road Diet Candidates
While some four-lane roads have too much traffic to be considered, the list of possible road diet candidates is flexible. Road diets reflect the needs of the community. Four lane roads with lower traffic volumes are identified as candidates for road diets. These roadways often reflect outdated needs for capacity in areas better served with a different street configuration. The Federal Highway Administration reports that road diets reduce aggressive speeding and cut collisions by nearly 30 percent.
Community Input
Seeking input and insight about the best use for roadways in your area is crucial. If you want a road diet in your area, you can submit a request through MyKCMO on your phone or our online portal.
Road Diet Terminology and Traffic Volume
A road diet (also called a lane reduction, road rechannelization or road conversion) is a technique in transportation planning whereby the number and/or the width of travel lanes of the road is reduced, often to achieve a reduction in crash rates. Počernická Street in Prague used to be four lanes wide. Reducing the number of lanes on a roadway cross-section is a typical road diet technique. 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) is 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, but more extensive reconstruction is needed.
Potential Misconceptions and Criticisms
Some claim that after a road diet in Pennsylvania, nearly 95% of those fearing the change were openly thankful, and that these changed roads " set the stage for millions or megamillions of dollars in new commercial and residential development." However, no formal studies have been conducted to verify this.
Emergency Response Concerns
The Iowa Department of Transportation, along with the CDC funded a study to change the perception of emergency response time in relation to road diets. The study looked at a single road dieted arterial in Cedar Rapids, Iowa and found no material improvement or reduction in response times.
Examples of Road Diets Worldwide
In the centre of Sinchon-dong, Seoul, (South Korea), a road diet has been achieved in 2014. After 6 months, traffic congestion eased substantially, leading to a reduction of accidents by 34% from the previous year. In a survey, visitor satisfaction in 2014 was at 70% (compared to 14% in 2013). During the COVID-19 pandemic London implemented a number of road diets to give more space to active travel modes such as bicycle lanes, on a number of its roads.
Unapproved Road Diets
Palo Alto, California has studied reducing the number of travel lanes to improve safety on some of its busiest streets since adopting a new Comprehensive Plan in 1998. Design plans were made for road diets on Embarcadero Road and Middlefield Road in the early 2000s, but were never brought to the city council for approval.
Road Diets in Florida and Vermont
In Tampa, Florida, Nebraska Avenue between its intersection with Hillsborough Avenue (US 92-US 41-FL 600) and Adamo Drive was reduced from four to three lanes, complete with bicycle lanes, a left turn lane and embedded bus stops for HART buses. In Rutland, Vermont, the city briefly converted Woodstock Avenue from a four-lane road to a three-lane road with bicycle lanes on each side.
Road Diets in Waverly, Iowa
In Waverly, Iowa the city converted Bremer Avenue from a four-lane road to a three-lane road with a safety buffer on each side. This conversion was done in 2018. According to Iowa DOT Crash Data and Iowa DOT AADT there was a 41% reduction in traffic on Bremer Avenue. Waverly did not see a crash reduction on Bremer Avenue. From (2014-2017) Bremer Avenue had 60 crashes under the 4 lane configuration, and that actually increased 5% to 63 crashes from (2021-2024). The majority of traffic from Bremer Avenue was diverted to 10th Avenue and Cedar River Parkway and crashes on those arterials went from 16 (2014-2017) to 75 (2021-2024), a 368% crash increase on the arterials where traffic was diverted to.
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