Safe speeds: roadway treatment technical toolkit

Speed management to prevent serious injuries and fatalities.

Table of Contents

How to use the toolkit

There is a clear link between speed and serious injury in crashes. That’s why a safe system approach is vital to the safety of everyone on the road. A safe system encourages safe speeds through roadway treatments to reduce potential crashes and associated injuries as much as possible. With physical and engineering-related roadway treatments effectively implemented, streets become self-enforcing, reducing speed related conflicts and serious crashes.

In this toolkit you will find basic information about roadway treatments strategies that you can put into action in your municipality and have been effectively implemented in Massachusetts. Once certain speed management measures are put into place, evaluation of speeds can be conducted to see if speeds have effectively changed and if people of all ages and abilities feel comfortable using the roadway. Efforts can always be made to further enhance the safety of our roadways through a phased approach of implementation, evaluation, and additional treatments and evaluation.

Read on and click through to discover physical and engineering-related measures to help you address speed-related concerns.

Establish a target speed

A target speed is the highest operating speed at which drivers should ideally operate on a roadway given a specific context. Over time, roadway features or uses can change, which may mean that practitioners need to revisit appropriate target speeds, rather than just defaulting to existing speed limits. In practice, these kinds of roadway evolutions can mean that while a driver may be adhering to the speed limit, they are still traveling at a speed too high for the roadway environment. As such, there is a need to evaluate the changing context and use of the roadway. Although speed limits are part of the equation, effective speed management requires a comprehensive plan that includes physical roadway features designed to control driving speeds.

In some instances, a target speed may be high and cannot be reduced. In these instances, separation of users is needed to make it safe through treatments like sidewalks, separated bike lanes, and protected intersections.

There are guides that can help you determine appropriate target speeds for your municipality. The National Association of City Transportation Officials provides a City Limits guide to help identify target speeds in many contexts.

Design features that can support safe speeds

Type of roadway treatment Description

Vertical deflection countermeasures

Speed humps, raised pedestrian crossings, or raised intersections that raise roadways for various lengths to slow drivers.

Horizontal countermeasures 

Median islands, chicanes or curves, or curb extensions that change the horizontal cross-section of a roadway. Chicanes are a series of curb extensions that alternate from one side of the street to the other, forming S-shaped curves that essentially narrow the roadway width and create an environment that slows down drivers.

Mini roundabouts and neighborhood traffic circles  Small-scale circular islands that act as a kind of intersection, offering yield-controlled entries and counterclockwise circulation in order to improve safety and reduce delays.

Road diets and marking measures 

Strategies such as perceptual speed markings, road diets, and lane narrowing. A road diet is a roadway configuration that involves narrowing or eliminating travel lanes to calm traffic speeds and increase safety of all roadway users. Road diets do not automatically impact throughput or cause congestion, and when it does safety is the preferred tradeoff.

Speed transition zones, advisory, and feedback signage 

Strategies to slow drivers traveling from a rural to an urban environment and signs that communicate recommended speed information and feedback to drivers.

Safe design for higher speed roadways

In some instances, a target speed may be high and cannot be reduced. In these instances, separation of users is needed to make it safe. Some examples of design features that can both protect all road users include: separated bike lanes, protected intersections, side paths, and safer crossings for pedestrians.

Share your speed management success 

If you’ve successfully implemented speed management measures in your community, please share your experience. Send information to MassDOT so that we can reach you to collect the details of your experience.

Vertical deflection countermeasures

Vertical deflection countermeasures are raised areas and bumps in the road that are designed to both slow vehicle speed and enhance safety for pedestrians by physically and/or visually marking crosswalks.

Features

Speed bumps/ humps/ cushions

Raised pedestrian crossings

Raised intersections  

By deflecting both the wheels and frame of a traveling vehicle, these features encourage drivers to travel at a slow speed in both directions, as well as over the speed bump itself.

These features provide a designated safe route for pedestrians across vehicular roadways where the pedestrian walking surface is raised to the same level—or close to the same level—as the sidewalks that access the pedestrian crossing.

These raised areas act as speed tables, covering an entire intersection with ramps on all vehicular approaches to slow vehicle traffic through the intersection and improve safety for pedestrians.

Speed hump across two lane road
raised pedestrian crossing across a two lane road
raised intersection at a 4-legged intersection

Costs & considerations

Feature Estimated cost* Percent speed reduction
Speed humps/bumps

$2,000, depending on drainage conditions and materials

14-34%
Raised crosswalks

$5,000-$7,000, depending on drainage conditions and materials

12-29%
Raised intersections

$25,000-$70,000

N/A

*Note: Estimates are based on past projects and commonly used materials, and may vary depending on roadway condition, location, time, and other factors. The speed reduction percentages were sourced from FHWA's Engineering Speed Management Countermeasures Table linked in the resources below.

Potential speed benefits

Vertical countermeasures have been found to effectively reduce the speed most people drive on a road. In one analysis, speed humps were found to reduce the 85th percentile speed by 22 percent on urban roads. (FHWA Speed Management Toolkit: Table 4)

These measures can also offer additional safety benefits, such as enhanced access for people with ambulatory disabilities, without impacting on-street parking or adjacent property if this is a concern. On one street in Cambridge, Massachusetts, installing raised devices increased the number of drivers who yielded to pedestrians from approximately 10% to 55%.

Visit the FHWA table on potential speed reduction for more information. While this data is all collected under differing circumstances and in different environments (volume of vehicles, rural vs. urban areas, etc.), it is still a helpful gauge for what each countermeasure can do.

Learn more 

When considering vertical countermeasures, it’s important to keep in mind the MassDOT Project Development Guidelines (Chapter 16). These are specific design policies and standards that you will need to adhere to, so that any changes you make meet federal and state guidelines. Keep in mind that these countermeasures should be considered as part of an iterative process; if a target speed is lower than vertical countermeasures can help realize, they may need to be implemented with other, concurrent measures. 

For example: 

  • Speed guidelines for these measures: e.g. roads with an 85th percentile speed over 30 mph, should not contain speed bumps/humps.
  • Speed humps height: typically 3-4 inches in height at their center, and 12-14 feet wide.
  • Pedestrian crossing slope: should not exceed 1:10 or be less steep than 1:25.
  • Maximum spacing between each speed bump/hump: 500 feet. 
  • Signage should alert snow-clearing vehicle drivers to raised speed reducers on the road.
  • Drainage design considerations.

Many of these details are included in Chapter 16 of our guide.

You can find more information about vertical countermeasures in these resources:

Horizontal countermeasures

By shifting the horizontal cross-section of a roadway, measures such as median islands, chicanes, and curb extensions are physical features designed to slow traffic and enable safe roadway access.

Features

Chicanes & lateral shifts 

Median islands

Curb extensions (bulb-outs)

A series of curb extensions that alternate from one side of the street to the other, forming S-shaped curves that essentially narrow the roadway width and create an effect that slows down traffic.

These roadway elements provide physical separation between opposing vehicle lanes, and narrow roadways to reduce vehicle speed.

For added pedestrian safety, these configurations prevent motorists from parking within or too close to a crosswalk, or from blocking a curb ramp.

Two lane roadway with lateral chicane.
Two lane road widening out with grass median in center
Landscape Curb extension on side of two lane road

Costs & considerations

Feature Estimated cost Percent speed reduction
Landscaped chicanes

Asphalt street: $10,000

Concrete street: $16,000

10-29%
Curb extensions

$2,000 to $20,000 per corner, depending on design and site conditions.

3-12%

*Note: Estimates are based on past projects and commonly used materials, and may vary depending on roadway condition, location, time, and other factors. The speed reduction percentages were sourced from FHWA's Engineering Speed Management Countermeasures Table linked in the resources below.

Potential speed benefits

Horizontal countermeasures have been found to effectively reduce the speed most people drive on a road. In one analysis, chicanes were found to reduce the 85th percentile speed by 16 percent on urban roads and 29 percent on other roads. (FHWA Speed Management Toolkit: Table 4)

These measures can also offer additional safety benefits, such as reducing cut-through traffic and shortening crossing distance for pedestrians, without significantly impacting access for emergency response vehicles as some vertical countermeasures may do (such as speed humps). 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 (BikePortland).

Visit the FHWA table on potential speed reduction for more information. While this data is all collected under differing circumstances and in different environments (volume of vehicles, rural vs. urban areas, etc.), it is still a helpful gauge for what each countermeasure can do.

Learn more

When considering horizontal countermeasures, it is important to keep in mind the MassDOT Project Development Guidelines (Chapter 16). These are very specific design policies and standards you'll need to adhere to, so that any changes you make meet federal and state guidelines.

For example:

  • When installing chicanes, you'll need to maintain enough width to allow emergency vehicles and trucks to pass through.
  • When using low cost, interim material to build curb extensions, you’ll need ensure adequate demarcation from the existing roadway using temporary curb, bollards, planters or striping.

Many of these details are included in Chapter 16 of our guide.

You can find more information about Horizontal countermeasures in these resources:

Mini roundabouts and neighborhood traffic circles

Features

Raised circular islands constructed in the center of residential street intersections, mini roundabouts and neighborhood traffic circles can reduce speed by directing drivers to maneuver around them. Sometimes used instead of stop signs, they are unsignalized measures designed to support low speeds.

Mini roundabouts have traversable islands and yield control on all approaches, so they function like other roundabouts. Neighborhood traffic circles are typically built at the intersections of local streets to provide traffic calming or aesthetic benefits. They operate as two-way or all-way stop-controlled intersections, typically without raised channelization to guide approaching traffic into the circulatory roadway.

Example photos  

 
Neighborhood traffic circle
Mini roundabout

Costs & considerations

Feature Estimated cost Percent speed reduction
Landscaped traffic mini-circle

Asphalt street: $6,000

Concrete street: $8,000-$15,000

12-42%

*Note: Estimates are based on past projects and commonly used materials, and may vary depending on roadway condition, location, time, and other factors. Estimates assume work can be accomplished within the roadway; costs will increase substantially if work requires ROW takings or curb displacement. The speed reduction percentages were sourced from FHWA's Engineering Speed Management Countermeasures Table linked in the resources below.

Potential speed benefits

Mini roundabouts and neighborhood traffic circles have been found to effectively reduce the speed most people drive on a road. In one analysis, mini traffic circles were found to reduce the 85th percentile speed by 11 percent on urban roads. (FHWA Speed Management Toolkit: Table 4)

Visit the FHWA table on potential speed reduction for more information. While this data is all collected under differing circumstances and in different environments (volume of vehicles, rural vs. urban areas, etc.), it is still a helpful gauge for what each countermeasure can do.

Learn more

When considering mini roundabouts and neighborhood traffic circles, it’s important to keep in mind the MassDOT Project Development Guidelines (Chapter 16). These are very specific design policies and standards you’ll need to adhere to, so that any changes you make meet federal and state guidelines

For example:

  • Neighborhood traffic circle islands are usually 12-16 feet in diameter.
  • The inscribed circles of mini-roundabouts are 45-90 feet with a design vehicle of an SU-30.
  • Circulatory signage should direct through traffic to proceed to the right of the circle.
  • The design vehicle for neighborhood traffic circles is a single truck with a 45-foot turning radius.

Many of these details are included in Chapter 16 of our guide.

You can find more information about Mini-roundabouts and neighborhood traffic circles in these resources:

Road diets and marking measures

Roadway configuration, along with visual cues for drivers, plays an important role in maintaining safe speeds and promoting traffic safety.

Features

Road diets Optical measures Lane markings
Narrowing or eliminating travel lanes on your roadways by installing road diets can help to calm traffic speeds. Visual cues can help focus drivers’ attention on their speed and draw their attention to the need to reduce speed for safety. Marked lanes can provide various benefits, such as reducing travel-lane width, or separating opposing traffic through target areas.
Road diet showing two lane road with two way center left turn lane
Two lane road with optical bars on right lane
hashed out shoulder on two lane road

Costs & considerations

Feature Estimated cost Percent speed reduction
Road diet restriping

$25,000-$40,000; geometric features increase cost significantly

4-9%
Optical markings

Low-cost and easy to install; actual costs vary

0-27%

*Note: Estimates are based on past projects and commonly used materials, and may vary depending on roadway condition, location, time, and other factors. The speed reduction percentages were sourced from FHWA's Engineering Speed Management Countermeasures Table linked in the resources below.

When considering cost, it is helpful to keep in mind 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.

Potential speed 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. (FHWA Speed Management Toolkit: Table 4)

These measures can also offer additional safety benefits and flexibility in terms of implementation. A pilot road diet was implemented in the town of 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 (MassDOT).

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 (BikePortland).

Visit the FHWA table on potential speed reduction for more information. While this data is all collected under differing circumstances and in different environments (volume of vehicles, rural vs. urban areas, etc.), it is still a helpful gauge for what each countermeasure can do.

Learn more

When considering road diets and marking measures, it’s important to keep in mind the MassDOT Project Development Guidelines (Chapter 16). These are very specific design policies and standards you’ll need to adhere to, so that any changes you make are consistent with MUTCD and other federal and state guidelines.

Many of these details are included in Chapter 16 of our guide.

You can find more information about Road Diets and Marking Measures in these resources:

Speed transition zones, advisory, and feedback signage

A transition zone is a series of measures placed over a distance to help drivers recognize that the roadway environment is changing—for example, from a rural to a suburban or urban area. This gives the driver enough time to reduce speed before entering the new zone. 

The goal of advisory and feedback speed signage and other countermeasures—such as curb extensions, raised crosswalks/intersections, raised medians, and landscaping—should be to incrementally reduce vehicle speeds. 

In order to be most effective, speed transition zones should be used before other speed management treatments are attempted. 

Here are some common approaches to speed transition zones:

Features

Signage

Common transition signs include reduced speeds ahead, pavement markings (such as optical speed bars and narrower lanes), regulatory or advisory speed limit signs, and speed feedback signs in strategic locations that alert drivers to their speed.

It is recommended that speed feedback signs be used alongside a regulatory or statutory speed limit signage to give context, and show drivers their speed in relationship to the legal speed limit.

Note: If you are using a statutory speed limit sign rather than regulatory, the speed feedback sign posted with it must have a yellow border. 

Speed Feedback sign with speed limit sign on two lane road
Horizontal & vertical elements

Within transition zones, horizontal features such as curb extensions and median islands convey a changing cross-section, while vertical measures, including speed bumps or raised pedestrian crossings, create natural speed reductions.

Curb bumpout at pedestrian crossing on two lane road
Enhanced crosswalks Typical crosswalks can be enhanced with high visibility crosswalk markings with colored pavement, a raised pedestrian crosswalk, pedestrian signage in the roadway, or a rectangular rapid flashing beacon.
Overhead view of enhanced crosswalk with high visibility markings and signals.

Costs & considerations

Feature Estimated cost Percent speed reduction
Dynamic speed feedback signs $2,000 to $12,000 per display; varies based on design and duration. 2-17%
Reduced speed limit signs $250-$1,000 per mile N/A

*Note: Estimates are based on past projects and commonly used materials, and may vary depending on roadway condition, location, time, and other factors. The speed reduction percentages were sourced from FHWA's Engineering Speed Management Countermeasures Table linked in the resources below.

Potential speed benefits

Speed transition zones, advisory, and feedback signage have been found to effectively reduce the speed most people drive on a road. In one analysis, signage and landscaping were found to reduce the 85th percentile speed by 7 percent at a neighborhood’s entrance. (FHWA Speed Management Toolkit: Table 4)

These measures can also offer additional safety benefits. In one FHWA speed feedback study, transitional signage was associated with a much greater decrease in crashes per quarter versus control sites without the signage. Separately, a before-and-after study of driver feedback signs on urban roads showed a 23 to 45 percent reduction in collision severity. Notably, driver reaction data also show that such signs are more impactful on non-workdays, when traffic volume is generally lighter, than on workdays.

Visit the FHWA table on potential speed reduction for more information. While this data is all collected under differing circumstances and in different environments (volume of vehicles, rural vs. urban areas, etc.), it is still a helpful gauge for what each countermeasure can do.

Learn more 

When considering speed transition zones, advisory, and feedback signage, it’s important to keep in mind the MassDOT Project Development Guidelines (Chapter 16). These are very specific design policies and standards you’ll need to adhere to, so that any changes you make meet federal and state guidelines.

For example:

  • Minimum letter height for changeable message signs should be 18 inches on roadways with speed limits of 45 mph or higher, and 12-inches for roadways with speed limits of less than 45 mph.
  • Speed limit signs have a minimum letter height of 4 inches.
  • The static portion of radar speed feedback signs should have a yellow background with black “YOUR SPEED” letters, and the changeable message portion should have a black background with yellow LEDs.

Many of these details are included in Chapter 16 of our guide.

You can find more information about speed transition zones, advisory, and feedback signage in these resources:

Take action and learn more

  1. Public: Reach out to municipal government to voice concerns and share speed management information.
  2. Municipalities: Work closely with members of the public and MassDOT to define areas where roadway safety can be improved. Additionally, municipalities initiate and implement speed management roadway treatments and speed zoning studies.
  3. MassDOT: Work closely with municipalities to help them conduct speed studies and implement speed management. MassDOT also signs official speed limits into law.

Contact

Online

MassDOT State Traffic Engineer StateTrafficEngineer@dot.state.ma.us

Address

10 Park Plaza, Suite 7520
Boston, MA 02116
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