Speed Management

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.

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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.
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  • 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.
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  • 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.
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  • 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.
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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.
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  • 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.
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  • 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.
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  • 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.
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  • 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.
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  • 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.
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    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.
    • 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.
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    • 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.
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    • 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
    When using horizontal speed management treatments, a minimum clear width of 12 feet for travel shall be maintained.
    Speed limits shall comply with local restrictions.
    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).
    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).
    Recommended Features
    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.
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    • Estimate travel time impacts on emergency vehicle response time, and define goals to evaluate during a trial.
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    • Implement speed management treatments on a trial basis, and work with emergency response officials to determine whether permanent features are appropriate.
    Speed management treatments should be used to reduce the street’s target speed to 20 mph.
    After speed management measures are implemented, posted speed limits should be reduced to match 85th percentile speed (5 mph speed increments are recommended).
    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.
    Vertical deflection features should be placed regularly along a corridor to reduce speeds.
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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).
    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
    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.
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    • 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.

Reference Publications