Throughout the 20th century, urban planners prioritized the quick and unobstructed flow of motor vehicle traffic. The motor vehicle reigned supreme. It is only within the last few decades that communities have begun to embrace more balanced spaces that encourage walking, cycling and outdoor social interaction.
Here we'll look at how traffic calming strategies create safer streets for everyone.
What is traffic calming?
Traffic calming is a road design strategy that encourages more attentive and responsible driving. It uses sensory-rich environments to reduce vehicle speeds—and to foster safe habits among all road users.
Why does it work? Traffic calming design forces drivers to pay attention to their whole driving environment—whether they know it or not—to determine their driving behavior. Factors like road conditions, obstructions, sight distance and the presence of pedestrians can seriously impact road safety. Traffic calming strategies are used to create environments where the most convenient driving behaviors are also the safest.
Modified streetscapes can help achieve a range of community goals, both functional and aesthetic, for the benefit of all street users. Traffic calming is especially valuable in areas with high pedestrian activity, such as crowded downtown streets, commercial districts, mixed-use spaces, recreational streets/boulevards and areas surrounding transportation hubs.
When implemented effectively, traffic calming can bring about a range of positive outcomes:
- Safer streets
- Reduced traffic noise
- Increased local economic activity
- Welcoming spaces for pedestrians and cyclists
- Increased universal access
- City beautification and revitalization
Street and lane width
One of the most natural means to encouraging slower driving is to reduce lane widths, as narrow lanes require more concentration and accurate steering. The simplest way to narrow traffic lanes is to move pavement markings, but roads can also be physically altered, creating opportunities for wider sidewalks and lanes for bikes or public transit.
Neckdowns are a popular form of road narrowing. A neckdown, also referred to as chokers or bulbs, can be installed at intersections or mid-block. Neckdowns are often used to define roadside parking bays, parallel or diagonal. They also reduce the distance for foot traffic crossing streets.
Sidewalk extensions can be used to provide space for amenities such as benches, trees, street lighting and kiosks. When used to contain parking bays, extension angles will affect vehicle access—sharp angles require parallel parking, while shallow angles accommodate back-in spaces.
When neckdowns are installed in series, alternating along either side of a street, they force vehicles to slalom between each extension. These installations are called chicanes. They work best with narrow lanes to prevent vehicles from cutting corners. Small medians can also be placed at intervals within chicanes to prevent vehicles from entering oncoming lanes.
Similar to narrow lanes and neckdowns, corners can be modified at intersections to create tight radii for vehicles. This forces vehicles to slow down to avoid traversing curbs or losing control. Tight corners, however, can be difficult for long vehicles and/or trailers to navigate.
How do bollards improve lane adjustments? Bollards offer clear visual elements that alert drivers to changes in lane patterns. Bollards are designed to sit at an ideal height for driver visibility while preserving safe fields of vision and long sightlines. Bollards can also be installed with security reinforcement to withstand vehicle impacts, which ensure protection for pedestrians and any other valuable street elements.
Flexible bollards can be used in conjunction with narrow lane markings. They retain the visibility advantage of traditional bollards, but will also avoid damage—to bollards, vehicles and surrounding pavement—in case of collision.
Roundabouts and traffic circles
Roundabouts and traffic circles are round islands installed in the middle of intersections to prevent straight-through traffic. They encourage steady, but regulated, flow—minimizing the start-stop patterns of traditional intersections. In terms of physical design, roundabouts don't require traffic lights (although, proper signage is important). Entry lanes can be installed to guide traffic into roundabouts.
Typically, roundabouts feature only a single lane, and rarely more than two, to prevent confusion among drivers. Traffic circles can be designed with sloped perimeters to reduce obstruction of long emergency vehicles and buses.
Roundabouts can be installed to accommodate a range of traffic scenarios and neighborhoods—although, unless significant space is available, they should be avoided in high-traffic arterial streets. For low-traffic intersections with available space, roundabouts can accommodate pedestrian crossings and other amenity features such as statues, fountains and community gardens.
How bollards improve roundabouts: Roundabouts often feature public art and landscape installations. Bollards can offer complementary design aesthetics while also protecting community assets. For traffic circles with regular foot traffic, bollards protect pedestrians by preventing vehicle access.
Medians and boulevards
Medians and boulevards occupy middle areas along roads, separating opposing lanes from oncoming traffic. They can be used to reduce lane widths and are typically cheaper to install than extending sidewalks.
Medians also provide a pedestrian refuge in the midst of busy, multi-lane roads and offer a natural barrier to prevent drivers from doing U-turns. Medians can be installed with fences to prevent pedestrians from crossing at unsafe areas. Like many other traffic management structures, medians can be landscaped with gardens and other greenery, or furnished with amenities and city art. As part of a larger traffic management plan, medians can also restrict the direction of traffic at intersections.
How bollards improve medians: Medians offer prime opportunities to regulate vehicle and pedestrian traffic. Bollards manage pedestrian flow when used in combination with continuous barriers such as fences or dense landscape elements—designating safe-passage for pedestrians while preventing vehicle access.
Diverters are physical barriers used to redirect traffic—which can be especially useful in residential areas. Similar to other structural barriers, diverters can be designed to accommodate passage for pedestrians and cyclists, and can incorporate decorative aspects such as greenery, lighting and other site furnishings. Diverters create significant disruptions to traffic flow, and should be used as part of a more comprehensive traffic management plan. Without proper planning, diverters can cause spillover traffic into nearby areas and may disrupt response times for emergency vehicles.
There are a range of diverter types that can be used for different configurations, which are typically installed at or around intersections.
- Diagonal barriers can be installed to traverse intersections to create two disconnected streets that turn away from each other.
- Semi-diverters restrict traffic flow in one direction, typically blocking road access from arterial streets into residential areas.
- Full diversions completely block access between arterial streets and quieter neighborhoods—often using cul-de-sacs to allow vehicle turnarounds in isolated streets.
How bollards improve diverters: Diverters often connect or extend pedestrian areas. They are especially useful in residential areas with high amounts of foot traffic. Bollards help ensure effective through-ways for pedestrians while reinforcing vehicle barriers. Look for unique designs to ensure aesthetics complement the character of surrounding neighborhoods.
Vertical deflections and surface treatments
Vertical deflections include all forms of speed bumps, speed humps, speed cushions and speed tables. Like other forms of traffic calming, vertical deflections offer passive enforcement. They create visual and physical discomfort for drivers, encouraging them to slow to an appropriate speed. Drivers who ignore these deflections risk severe discomfort and potential damage to their vehicles.
The shape and size of deflections affect vehicle speeds. Large bumps with steep inclines are more disruptive, while small bumps with shallower deflections are less intrusive. Speed bumps are typically the most intrusive intervention for vehicles, while speed humps, speed cushions and speed tables create milder disruptions. Deflections can be formed using concrete or asphalt, but preformed, bolt-down products are also available for easy and consistent installation.
Surface treatments also slow vehicles. Rumble strips are common interventions that offer tactile cues, encouraging drivers to reduce speeds to avoid significant vibrations. They also provide visual cues, which can be used to identify crosswalks. Surface treatments can be installed in series across road surfaces to slow vehicles over a larger area, or alert drivers entering sensitive areas. Prefabricated rumble strips can be installed in pavement, but various forms of cobblestones and pavers are also common.
How bollards improve vertical deflections and surface treatments: Bollards can be used to prevent vehicles from circumventing obstructions, and to better identify them for drivers. Surface treatments are ideal in areas surrounding crosswalks, where bollards can identify and protect pedestrian waiting areas—especially around curb extensions.
As a company that specializes in outdoor site furnishings, we believe that bollards have a strong role to play in complementing many of the most common and effective traffic designs. Aside from improving safety, bollards are designed to regulate interactions between vehicles, pedestrians and other forms of traffic.
A range of bollard styles are available to complement surrounding street and building designs—offering a better sense of place for local residents and commercial visitors.
Traffic Calming: Moving Beyond the Automobile
Looking for more information on how to control traffic in your community? This video discusses how alternative modes of transportation can ease congestion and lower vehicle speeds.
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- Massachusetts Traffic Safety Research Program. "Report on Passive Speed Control Devices". Governor's Highway Safety Bureau Executive Office of Public Safety. August 2004.
- Institute of Transportation Engineers and the Federal Highway Administration. Traffic Calming: State of the Practice. August 1999.
- Project of Public Spaces. "Traffic Calming 101." pps.org
- San Francisco Planning Department. "SF Better Streets." sfbetterstreets.org
- San Francisco Planning Department. "Chapter 6: Streetscape Elements". San Francisco's Better Streets Plan. January 2011.
- Traffic Logix. "Traffic Calming". trafficlogix.com
- Transportation Alternatives. "Rethinking Bollards: How Bollards Can Save Lives, Prevent Injuries and Relieve Traffic Congestion in New York City". transalt.org. July 2007.
- Transportation Demand Management Encyclopedia. "Traffic Calming Roadway Design to Reduce Speeds and volumes". vtpi.org (updated April 15, 2015)
- Roads aren't always designed for multiple users: Joiseyshowaa, CC BY-SA 2.0, via Flickr
- Curb extensions in a residential neighborhood: Richard Drdul, CC BY 2.0, via WikiCommons
- Chicanes force vehicles to slalom around obstacles: Richard Drdul, CC BY 2.0, via WikiCommons
- Sharp turns force vehicles to reduce speed: Richard Drdul, CC BY 2.0, via WikiCommons
- Traffic circles often feature prominent design elements: Averette, CC BY 3.0, via WikiCommons
- Medians separate divide oncoming lanes: Nyttend, Public Doman, via WikiCommons
- Partial road diverter with bike lane: Richard Drdul, CC BY 2.0, WikiCommons