Since the publication of the NACTO Urban Bikeway Design Guide, NACTO has released additional guidance on facility selection where goals include high-comfort or all-ages bicycling.
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Description
Speed Management measures for bicycle boulevards bring motor vehicle speeds closer to those of bicyclists. Reducing speeds along the bicycle boulevard improves the bicycling environment by reducing overtaking events, enhancing drivers’ ability to see and react, and diminishing the severity of crashes if they occur. Speed management is critical to creating a comfortable and effective bicycle boulevard.
Streets developed as bicycle boulevards should have 85th percentile speeds at 25 mph or less (20 mph preferred). Speed management (traffic calming) measures can be divided into vertical or horizontal features. These measures can be implemented individually or in combination to increase their efficacy. Common combinations include raised crosswalks with pinchpoints, raised intersections with pinchpoints, and speed humps with center island narrowings, chicanes, or pinchpoints.
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Reduced Speed Limits
Bicycle boulevards should have a maximum posted speed of 25 mph. Some jurisdictions are starting to sign residential speed limits below 25 mph. Simply changing the speed limit is unlikely to reduce speeds; speed management and street design techniques are necessary. Once actual speeds decrease, lower speed limit signs can reinforce the desired speed with regulatory control. Targeted enforcement is also recommended.
Reduced speed limits may require authorizing legislation. The MUTCD designates that speed limits shall be in increments of 5 mph and requires an engineering study to reduce the speed below the statutory speed for the type of roadway. In some jurisdictions, speed limits may be reduced beyond the statutory residential speed limit. State statutory limits might restrict the maximum speed limit that can be established on a particular road. Read More+
As of 2012, Oregon cities have authority to lower the speed limit on residential streets to 20 mph if the road has an average volume less than 2,000 vpd, an 85th percentile speed of less than 30 mph, and if there is a device (e.g., shared lane markings, warning signs) that indicates the presence of bicyclists or pedestrians. City of Portland staff intend to sign all residential neighborhood greenways that meet these criteria at 20 mph and have begun implementing speed management measures to create streets with target speeds of 20 mph in anticipation of the lowered speed limit.
Albuquerque, NM, signs bicycle boulevards at 18 mph but has not used speed management to reduce the streets’ speeds. Targeted enforcement is used when a bicycle boulevard first opens, and electronic speed feedback signs reinforce the speed limit to drivers.
In California, the prima facie speed limit in residential areas is 25 mph, which is the lowest speed limit allowed allowed, with specific exceptions. In order to enforce speed using a radar, a city must conduct a speed survey to justify the speed limit. Cities can post advisory speeds, such as a triangular, yellow 15 mph sign with a speed bump warning sign.
Vertical Deflection
Vertical speed control measures are composed of wide, slight pavement elevations that self-enforce a slower speed for motorists. Note: the type of narrow, abrupt speed bumps used in private driveways or parking lots are not recommended for public streets and are a hazard to bicyclists. Some examples of recommended speed management treatments include the following:
- Speed humps are 3 to 4 inches high and 12 to 14 feet long, such that speeds are reduced to 15 to 20 mph. They are often referred to as “bumps” on signage and by the general public. Read More+
Speed humps should be no more than 500 feet (152 m) apart or between slow points where the desired 85th percentile operating speed is between 25 and 30 mph.
Institute of Transportation Engineers. (2011). Updated Guidelines for the Design and Application of Speed Humps and Speed Tables.
“Improperly designed, speed humps and all speed bumps are dangerous for bicyclists… both 3-inch and 4-inch humps are likely to be safe for bicyclists, although the 4-inch hump should probably be used with caution where bicycle traffic is frequent or rapid. … Speed humps should be located far enough from intersections that turning cyclists are no longer leaning when they encounter the hump.”
Speed humps should be used with caution on hills where bicyclist speeds may exceed 20 mph. The City of Oakland, CA, only installs speed humps on streets with a vertical grade less than 5 percent.
DeRobertis, M., and Wachtel, A. (1996). Traffic Calming: Do’s and Don’ts to Encourage Bicycling.
- Speed cushions or speed lumps are either speed humps or speed tables that include wheel cutouts to allow large vehicles to pass unaffected, while reducing passenger car speeds. They can be offset to allow unimpeded passage by emergency vehicles and are typically used on key emergency response routes. They should be used with caution, however, as people driving sometimes seek out the space between the lumps, reducing the traffic calming effect and causing unpredictable driving. Read More+
“Speed lumps reduce the 85th percentile speed by 25 percent, or 9 mph… The speed reduction with lumps is comparable to that with speed humps.”
Speed lumps or cushions have been found to have minimal, if any, impact to emergency vehicles in Austin, TX, and San Diego, Sacramento, and Danville, CA.
Gulden, J., and Ewing, R. (2009). New Traffic Calming Device of Choice.
On a 36-foot wide roadway, three lumps are optimal, with a 6-foot wide center lump to minimize emergency vehicle delay and discomfort, and the outside lump widths can vary. The wheel gaps should be 1 to 2 feet wide. This configuration also allows bicyclists to pass through the speed lumps without having to leave the center of the lane; the City of Seattle marks shared lane marking arrows at the gap to guide bicyclists.
Ewing, R. and Brown, S. (2009). U.S. Traffic Calming Manual.
“Speed cushions do not present any notable disadvantages for emergency vehicles.”
Berthod, C. (2011). Traffic Calming: Speed Humps and Speed Cushions.
Parking alongside speed lumps may be restricted to enable bicyclists to pass through the outside of the feature.
- Speed tables are longer than speed humps and flat-topped, with a height of 3 to 3.5 inches and a length of 22 feet. Vehicle operating speeds range from 25 to 35 mph, depending on the spacing, and speed tables may be used on collector streets and/or transit and emergency response routes.
- Split speed tables are also 22 feet long and extend across one direction of travel lanes from the centerline. A longitudinal gap is provided to allow emergency vehicles to weave around the treatment. While studies have indicated that this treatment does not reduce speeds below 25 mph, it has been found to deter cut-through traffic, particularly by large trucks. Read More+
“After several runs, it was decided that the distance between the two lane bump halves needed to be at least 28 feet for the vehicle to maneuver through at or near 20 mph.”
Mulder, K. (1998). Split Speed Bump.
- A raised crosswalk is a speed table that is marked and signed for pedestrian crossing. It extends fully across the street, can be longer than a typical speed table, and is typically 3 inches high. An entire minor intersection can be raised to reduce motor vehicle speeds in all directions. Read More+
“Granite and cobblestone finishes are not recommended [for raised crosswalks] because, although aesthetically pleasing, the surface may become slippery when wet, and may be difficult to cross for pedestrians who are visually impaired or using wheelchairs.”
Parkhill, M., Sooklall, R., and Bahar, G. (2011). Updated Guidelines for the Design and Application of Speed Humps.
Raised crosswalks are 3 inches below the level of standards sidewalks, and an accessible curb ramp should be provided, as well as a surface textural indication for pedestrians with vision impairments.
Ewing, R. and Brown, S. (2009). U.S. Traffic Calming Manual.
Horizontal Deflection
Horizontal speed control measures cause motorists to slow down in response to either a visually narrower roadway or a need to navigate a curving travel lane. Where traffic calming features do not extend beyond the parking lane, they visually narrow the road and improve the approaching bicyclists’ view of cross traffic, but do not act as speed management. When motor vehicle speeds are already below target thresholds, elements can either extend into the travel lane or narrow a bi-directional street to a single lane. Under these conditions bicyclists are comfortable taking the lane and overtaking cars do not encroach on bicyclists’ space. Where possible, provide sufficient space for bicyclists to pass around the outside of the elements.
Examples of horizontal deflection include the following:
- Curb extensions or bulb-outs extend the sidewalk or curb face into the parking lane at an intersection. When placed on the bicycle boulevard, they visually narrow the roadway. Curb extensions on the cross street act as a minor street crossing. All curb extensions reduce the crossing distance for pedestrians, can increase the amount of space available for street furniture and trees, and can act as stormwater management features.
- Edge islands are curb extensions that leave a 1- to 2-foot gap by the curb to improve drainage.
- Neighborhood traffic circles are minor street crossing treatments that also provide speed management. They are raised or delineated islands placed at intersections that reduce vehicle speeds by narrowing turning radii, narrowing the travel lane, and, if planted, obscure the visual corridor along the roadway. It should be noted that the City of Portland has found such circles to be less effective than frequently spaced speed humps, and many people on bicycles complain that motorists overtake them when approaching the circles, creating a hazardous condition. Read More+
The number of automobile accidents at intersections [with traffic circles] fell 94 percent….Accident reduction was also found in subsequent years.
Mundell, J. (No Date). Neighborhood Traffic Circles.
Neighborhood traffic circles can include a paved apron or mountable curb to accommodate the turning radii of larger vehicles like fire trucks or school buses. Larger circles should include splitter islands at the approaches. Vehicles over 22 feet may be allowed to turn left in front of traffic circles in some states; others expressly prohibit this movement.
Traffic circles at T-intersections should include curb extensions before and after the intersection or use curb indentation at the top of the T to provide the same deflection benefits as at 4-way intersections.
Ewing, R. and Brown, S. (2009). U.S. Traffic Calming Manual.
The circle should be landscaped to attract attention and for aesthetic reasons; trees should have clear stem heights of at least 8 feet and be no more than 4 inches in diameter, while other plantings should be no more than 2 feet high.
Stop signs may be used in conjunction with traffic circles, but are not mandatory.
Some jurisdictions use yield signs, while others discourage use of both stop and yield.
- Chicanes are a series of raised or delineated curb extensions, edge islands, or parking bays on alternating sides of a street forming an S-shaped travel way. This reduces vehicle speeds by requiring drivers to shift laterally through narrowed travel lanes. Read More+
Curb extensions and edge islands should be tapered at 45 degrees to reinforce the edge lines and should use plantings to increase their visibility.
Edge lines should be marked to designate the travel lane.
A landscaped center island may be used to separate opposing traffic and discourage drivers from crossing the centerline.
On narrow streets with low parking turnover, parking bays may be used to create the lateral shift.
- A pinchpoint or choker narrowing includes curb extensions or edge islands placed on either side of the street to narrow the center of the lane such that two drivers have difficulty passing through simultaneously. Pinchpoints should only be used where traffic speeds are already low. Cut-through passageways should be provided to the outside of the pinchpoint to accommodate bicyclists. Read More+
Pinchpoints should provide a clear two-way travel path of less than 18 feet (12 feet recommended).
Curb extensions and edge islands should be tapered at 45 degrees to reinforce the edge lines and use plantings to increase their visibility.
- Neckdowns are pinchpoints at intersections; they are minor street crossing treatments that narrow at least one side of an intersection using curb extensions or edge islands on both sides of the street. They are often combined with parking bays on side streets off of commercial main streets. Read More+
The curb radius of neckdowns on local streets should be approximately 20 feet.
Stop lines on side streets may be set back from intersections such that turning trucks can briefly cross into the opposing lane.
- A short center island narrowing is a median parallel to the bicycle boulevard that causes a small amount of deflection without blocking driveway access (such treatments can also act as median refuge islands for pedestrians crossing the bicycle boulevard, but in this configuration it is not a crossing treatment for the bicycle boulevard). Medians can be used for volume management and to assist in bicycle turns at offset intersections. Read More+
Center island narrowings should be large enough to command attention – at least 6 feet wide and 20 feet long.
Ewing, R. and Brown, S. (2009). U.S. Traffic Calming Manual.
In addition to the above retrofit treatments that narrow a street, some jurisdictions are building skinny streets or queuing streets, which are between 20 and 28 feet wide (with parking).
On-street parking should be prohibited within 20 to 50 feet of the right-hand side of intersections to accommodate turning movements and increase visibility.
- Skinny streets or queuing streets are narrow residential streets that require low motor vehicle speeds and accommodate travel in a bi-directional lane. These types of streets calm traffic as drivers must yield to each other to allow one direction of travel at a time to pass. Read More+
On-street parking should be prohibited within 20 to 50 feet of the right-hand side of intersections to accommodate turning movements and increase visibility.
Seattle’s standard, low-volume, non-arterial streets are 25 feet wide when parking is allowed on both sides.
Click on the images below to view 3D concepts of speed management treatments.
Treatment details can be accessed below under design guidance.
Speed Management Benefits
- Decreases motor vehicle speeds. Read More+
- Decreases the likelihood that crashes will occur, by increasing drivers’ response time and minimizing motor vehicles overtaking movements.
- Decreases the likelihood of an injury resulting from a crash. Read More+
- Improves bicyclist comfort and benefits pedestrians and residents by reducing traffic speeds along the corridor.
- Establishes and reinforces bicycle priority on bicycle boulevards by discouraging through vehicle travel.
- Provides opportunities for landscaping and other community features such as benches, message boards, and colored pavement in the intersection, benefiting all roadway users and residents.
Typical Applications
- Bicycle boulevards where motor vehicle speeds are at or above posted speed or established target speed. Read More+
In general, a speed differential between motor vehicles and cyclists of no more than approximately 15 mph is desirable.
[Note: this refers to the difference between a person on a bicycle traveling at 10 mph and a motorist at 25 mph. Smaller differential is desirable.]
Alta Planning + Design and Portland State University Initiative for Bicycle and Pedestrian Innovation. (2009). Bicycle Boulevard Planning & Design Guidebook.
- Streets where the neighborhood feels traffic speeds are too high and are supportive of speed management treatments.
- Streets where minor street crossing improvements to reduce bicycle delay (e.g., flipping stop signs to favor the bicycle boulevard) may otherwise encourage higher motor vehicle volumes and/or speeds.
- At high-use pedestrian crossings of a bicycle boulevard (raised crosswalk or intersection).
- Anywhere green infrastructure or sewer improvements are desired; bioswales can be integrated into the design of curb extensions, chicanes, pinchpoints, and narrowings.
Design Guidance
Click the image above to see the guidance summary page full screen.
See MUTCD Chapter 3I for guidance on marking and signing islands and other features. The Delaware Department of Transportation has also developed standard signs and pavement markings for traffic calming features following MUTCD guidelines.
See ITE’s U.S. Traffic Calming Manual (Ewing and Brown, 2009) for guidance on use of speed and volume management techniques.
| Required Features |
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When using horizontal speed management treatments, a minimum clear width of 12 feet for travel shall be maintained. |
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Speed limits shall comply with local restrictions. |
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Speed zones (other than statutory speed limits) shall only be established on the basis of an engineering study that has been performed in accordance with traffic engineering practices (MUTCD 2B.13). |
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Speed limits shall be in multiples of 5 mph and signs shall be located at the points of change from one speed limit to another (MUTCD 2B.13). |
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Emergency services should be in sync with transportation departments in recognizing that reducing speed and volume on local roadways, in addition to getting more people on foot and bike and out of cars, benefits their overall safety goals by reducing crash frequency and severity. The primary way of doing this is to develop an emergency response route classification map at the onset of the planning process, as discussed in route planning. Emergency vehicle response times should be considered where vertical deflection is used. Because emergency vehicles have a wider wheel base than passenger cars, speed lumps/cushions allow them to pass unimpeded while slowing most traffic. Strategies include the following:
- Seek approval by emergency response officials for treatments on emergency response routes.
- Allow a limited set of emergency-vehicle-friendly traffic calming techniques on emergency response routes. Read More+
Emergency-vehicle-friendly treatments can include 22-foot speed humps, split humps (laterally offset speed tables), speed lumps/cushions (which have a gap that accommodates emergency vehicles’ wheels), or speed humps with a configuration of three lumps with a six-foot-wide center lump with one or two foot wheel gaps.
Ewing, R. and Brown, S. (2009). U.S. Traffic Calming Manual.
- Estimate travel time impacts on emergency vehicle response time, and define goals to evaluate during a trial.
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For a maneuverability test, cones are placed in the street to model the proposed dimensions of the treatments or street reconfiguration. Typical emergency response vehicles are then driven through the area, using every possible turning movement. Travel time tests should be discouraged. Research has shown a large variance between speeds with simulated devices (represented by cones) and actual devices as constructed.
Ewing, R and Brown, S. (2009). U.S. Traffic Calming Manual.
- Implement speed management treatments on a trial basis, and work with emergency response officials to determine whether permanent features are appropriate.
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Speed management treatments should be used to reduce the street’s target speed to 20 mph. |
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After speed management measures are implemented, posted speed limits should be reduced to match 85th percentile speed (5 mph speed increments are recommended). |
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The impacts to traffic on adjacent streets should be monitored; while speed management treatments primarily affect motor vehicle speeds, they also reduce volumes, as drivers tend to avoid slower streets.
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Vertical deflection features should be placed regularly along a corridor to reduce speeds.
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Speeds increase about 0.5 to 1.0 mph for every 100 feet of separation for hump spacing up to 1,000 feet.
Ewing, R. (1999.) Traffic Calming: State of the Practice. Institute of Transportation Engineers.
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Guidance for vertical traffic calming features:
- Slopes should not exceed 1:10 or be less steep than 1:25.
- Side slopes on tapers should be no greater than 1:6 to reduce the risk of bicyclists losing their balance.
- The vertical lip should be no more than a quarter-inch high (Ewing, 2009).
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Horizontal speed control measures should not infringe on bicycle space. Where possible, provide a bicycle route outside of the element to avoid bicyclists having to merge into traffic at a narrow pinchpoint. This technique can also improve drainage flow and reduce construction and maintenance costs. |
| Optional Features |
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Speed management may be implemented on a trial basis to gauge residents’ support prior to finalizing the design. Temporary speed humps, tables, and lumps are available. Temporary traffic calming should be used with caution as they can diminish residents’ opinions due to unappealing design and reduced functionality. |
Maintenance
- In cities with snowy winters, traffic calming should be designed to minimize impacts to snow removal operations through the use of reflective delineators on horizontal treatments and sinusoidal transitions to vertical treatments that allow plow blades to track over the change in elevation. Temporary traffic control devices can be used and may be removed in the winter, when speeds are generally slower. Read More+
“In 92% of cases where the measure is permanent, it remains as effective at slowing speeds in the winter as in the summer. In 79% of cases, there was no deterioration resulting from winter conditions or snow removal. In 71% of cases, snow removal did not pose any problems. … A sinusoidal shape is preferred over a circular or parabolic shape because it provides a more gentle transition and is easier for winter maintenance operators and cyclists to negotiate.”
Berthod, C. (2011). Traffic Calming: Speed Humps and Speed Cushions.
- Vegetation should be regularly trimmed to maintain visibility and attractiveness.
Treatment Adoption and Professional Consensus
Many cities in the U.S. have neighborhood traffic calming programs or public works departments that have installed speed humps or traffic circles. Cities that have designated bicycle boulevards have implemented a variety of speed management treatments. Just greater than half of the jurisdictions with traffic calming programs surveyed for the U.S. Traffic Calming Manual (Ewing, 2009) use trial installations to test speed and volume management techniques.