Figure 9-1. Half closures placed at intersections are a traffic calming technique intended to divert motorists off of residential streets by closing one-half the roadway and allowing one-way traffic. Half closures reduce crossing distances for pedestrians.
Traffic calming utilizes design strategies to slow down cars and increase the visibility of pedestrians and bicyclists. The tools of traffic calming are small in scale and, as a result, are able to be tested, photographed, and evaluated easily. Traffic calming has proven to reduce traffic speeds and, consequently, reduce the number of pedestrian deaths. Traffic calming tools particularly complement areas that already have well-designed sidewalks. If adequate sidewalks are not provided and pedestrians are forced to travel in the street, traffic calming tools can be problematic for people with impairments. For example, vertical installations, such as speed humps, force pedestrians to negotiate an elevation change. Horizontal installations, such as neighborhood traffic circles, may cause pedestrians to be "squeezed" by vehicles. To best serve the needs of pedestrians, sidewalk facilities should be improved in conjunction with traffic calming projects.
The goals of traffic calming are to:
In most localities, the immediate and long-term goals of traffic calming are directly related to the concerns of the residents. Parents and citizens are demanding that speeds be reduced and cut-through traffic eliminated, particularly on residential streets near schools and parks. In many communities, citizens have conveyed their traffic-related concerns to local leaders who, in turn, have sought direction from transportation experts to implement traffic calming measures.
Increased pedestrian awareness, slower moving traffic, and fewer vehicles on the road are the direct benefits of traffic calming. These benefits may allow people with disabilities to achieve greater access to roadways and pedestrian facilities. For example, the implementation of traffic calming techniques at pedestrian crossings to reduce crossing distances improves conditions for pedestrians, especially those with mobility, cognitive, and vision impairments. Pedestrians benefit from reduction in traffic speed and volume control measures, which can create entirely traffic-free sections of communities and urban areas.
Although many traffic calming techniques benefit people with disabilities, some techniques can have a negative impact especially if their needs are not addressed during the planning process. For example, tools such as roundabouts and raised crosswalks can eliminate the crossing gap and sidewalk to street transition information for people with vision impairments. Other methods such as speed humps and textured pavement can be problematic for people with mobility impairments. Fortunately, many of these traffic calming tools can be designed and implemented with accessible modifications that should become the universal standard for constructing these devices.
The following sections briefly describe each device, discuss the impacts the device has on pedestrian access, and make recommendations for enhancing pedestrian accessibility.
The primary purpose of volume control measures is to discourage or eliminate cut-through traffic. When a detour through a residential neighborhood allows motorists to avoid traffic, save time, or shorten their travel distance, they will use the residential cut-through as their normal route of travel. The traffic calming tools that have proven to be successful in diverting traffic and reducing cut-through traffic include:
Full street closures are barriers placed across the entire width of the street. Consequently, through traffic is diverted from using the street, and the street is only open to pedestrians, bicyclists, and the residents living on the street. A full closure functions similar to a cul-de-sac or dead-end because these designs include only one point of entry/exit minimizing cut-through traffic. Full closure barricades are usually landscaped walls, gates, side-by-side bollards, or other constructed obstructions. Full closures should be designed to allow access for bicyclists.
Full closures do not have a specific impact on pedestrian access; however, they improve conditions for pedestrians in general by creating a street where only motor vehicles traveling on the street are owned by people living on the closed street.
The following recommendations are intended to enhance access at a full closure:
Half street closures are similar to full closures and consist of constructed obstructions to block one side of the street. One direction of traffic is diverted to another route. Half closures are often called partial closures or one-way closures. They are constructed using the same materials and designs as full closures.
Half closures generally benefit pedestrian access as follows:
Half closures should always be designed as curb extensions to reduce pedestrian crossing distances.
Median barriers are raised islands located in the middle of a street and continuing through an intersection. Median barriers are implemented to block cut-through movement of motor vehicle traffic at a cross street. Median barriers can block left turning motorists, which can benefit pedestrians. They are also called median diverters or island diverters. For general information about medians, see Section 8.7.
Median barriers generally benefit pedestrian access as follows:
The following recommendations are intended to enhance pedestrian access at median barriers:
Figure 9-6. Forced turn islands should be designed to include features that promote access such as cut-through medians with detectable warnings and a minimum width of 915 mm (36 in).
Forced turn islands are also called forced turn channelizations, pork chops, or right turn islands. They prevent traffic from certain movements when approaching an intersection. For general information about islands, see Section 8.8.
Although forced turn islands have some benefits for people with mobility impairments, they are not as desirable as median barriers for diverting traffic because they complicate the intersection for people with vision impairments. Forced turn islands impact pedestrian access as follows:
The following recommendations are intended to enhance pedestrian access at forced turn islands:
Two types of traffic calming measures that control the speed of vehicles on streets and impact pedestrian access are (Institute of Transportation Engineers, 1999):
A third form of speed control is a narrowing measure, which relies on a psycho-perceptive sense of enclosure to discourage speeding. Installing a tree canopy to create a sense of enclosure is an example of a narrowing measure. This type of traffic calming does not impact pedestrian access if a sidewalk is provided. A 915 mm (36 in) clear space on both sides of the street allows for bicyclists to travel through. The general benefits of slower motorist speeds benefits all pedestrians.
Vertical speed control measures that will be evaluated in the following sections include:
Horizontal measures that will be evaluated in the following sections include:
Speed humps are raised sections of pavement that are placed across the street to force motorists to travel at reduced speeds. Speed humps have a more gradual slope than traditional speed bumps, which are often found in parking lots. Speed humps are more effective at slowing traffic than speed bumps because the driver actually benefits from traveling at slower speeds. Speed bumps typically jar the motorist regardless of speed. The best speed hump designs employ a very gradual slope, such as a 3.66 m (12 ft) long speed hump with a 101 mm (4 in) vertical elevation change, to reduce jarring and potential vehicle damage. Speed humps are effective in reducing traffic speeds and are a low cost tool. However, speed humps may be controversial in some localities due to their appearance and jarring effects on vehicles and passengers.
Figure 9-9. A 3.66 m (12 ft) long speed hump with a 101 mm (4 in) vertical elevation change minimizes the jarring effect and potential vehicle damage experienced with traditionally designed speed bumps.
In general, speed humps effectively slow traffic and benefit all pedestrians including people with disabilities. However, people with mobility impairments may experience problems on speed humps. For example, people with back or neck problems may experience pain or discomfort caused by the jarring effect when traveling over speed humps in an automobile. This is further complicated if the person relies on para or public transit and does not have control over the speed of the vehicle.
The following recommendations are intended to enhance pedestrian access at speed humps:
Speed tables are similar to speed humps; however, they include a flat section on top. Oftentimes, the top of the speed table is constructed with a decorative surface material. When marked as a pedestrian crossing, speed tables are called raised crosswalks. The length of speed tables or raised crosswalks allow all four wheels of a vehicle to rest on the raised section at the same time. Combined with gently sloped ramps, speed tables permit slightly higher motorist speeds and smoother transitions than speed humps. Additional information about raised crosswalks is contained in Sections 6.3 and 8.5.
Figure 9-10. Speed tables and raised crosswalks are flush with the curb and do not provide a clear distinction for people with vision impairments unless detectable warnings are installed.
Speed tables resolve some of the access problems for people with mobility impairments. However, they can be problematic for people with vision impairments if their needs are not considered. Speed tables impact pedestrian access as follows:
Note: When used as a crosswalk, there is no negative impact on pedestrians with visual impairments when detectable warnings are installed.
The following recommendations are intended to enhance pedestrian access at speed tables and raised crosswalks:
A raised intersection refers to a roadway intersection that is entirely elevated to the sidewalk level. Raised intersections are designed with ramps for the motorist and often include decorative surface materials on the flat raised section. Raised intersections are usually the same height as the sidewalk creating a pedestrian territory that includes the sidewalk and crosswalks.
Raised intersections have benefits and drawbacks that are similar to raised crosswalks. For example:
Figure 9-11. When raised intersections are installed, detectable warnings should be included at the edge of the curb so people with vision impairments can identify the transition between the sidewalk and the street.
The following recommendations are intended to enhance pedestrian access at raised intersections:
Textured pavement is a surface material on the roadway, such as brick, concrete pavers, and stamped asphalt, which is installed to produce small, constant changes in vertical alignment. Textured pavements do reduce travel speeds; however, they are difficult for bicyclists and some pedestrians to negotiate (see Section 184.108.40.206).
Figure 9-12. When textured pavements are used, wheelchair users experience discomfort during travel and people with vision impairments have difficulty identifying detectable warnings.
Figure 9-13. A modern roundabout should have set back crosswalks and splitter islands to better accommodate pedestrians. However, even with these design improvements, people with visual impairments experience difficulty negotiating roundabouts.
Textured pavement is problematic for people with disabilities. For example:
Due to negative impacts on pedestrians and access, the installation of large areas with textured pavement at intersections and midblock crossings should be avoided as a traffic calming tool.
Roundabouts require vehicles to circulate counterclockwise around a center island. Roundabouts may eliminate the need for traffic signals for motorists. Unlike many other forms of traffic calming, roundabout benefits are aimed primarily at motorists. The installation of roundabouts prioritizes improving traffic flow, maximizing vehicular capacity, and eliminating the need for stop signs and traffic signals. When designed correctly, roundabouts include raised splitter islands to channel incoming traffic approaching from the right. Although roundabouts are gaining popularity in the United States, they can be problematic in pedestrian areas until designs can include cues needed by pedestrians with vision impairments and cognitive disabilities.
Figure 9-14. This drawing illustrates a common roundabout design found in Sweden that includes large grass buffers that separate pedestrians and motorists at exit and entry points. The crosswalks are set back about four car lengths to reduce pedestrian and motorist conflicts.
Roundabouts significantly complicate travel for people with vision and cognitive impairments. For example:
Figure 9-15. Urban single lane roundabout with splitter island for pedestrian refuge. Truncated domes need to be placed at the curb ramps and splitter island. Landscape barrier, guidance cue at curb ramps, and APS are needed for crossing information, safety, and accessibility.
Designing roundabouts for people with vision impairments is a topic that warrants significant future research. Some smaller roundabouts may prove to pose few problems for people with vision impairments, but that depends on how busy or quiet it is. Some smaller roundabouts in quiet or isolated environments may prove to pose fewer problems for people with vision impairments. However, other roundabouts, in busy and noisy environments, may be identified as unusable by people with vision impairments regardless of the additional treatments used. The following recommendations could potentially improve conditions for pedestrians at roundabouts:
Neighborhood traffic circles are similar to roundabouts in that traffic is required to circle around a center island counterclockwise. Neighborhood traffic circles are typically controlled by YIELD signs but may be controlled by STOP signs. Traffic circles are often located on lower volume residential streets. Traffic circles are the most common horizontal measure of traffic calming.
Although they are not as problematic as roundabouts, neighborhood traffic circles still have a negative impact on pedestrian access:
The following recommendations are intended to enhance pedestrian access at neighborhood traffic circles:
Chicanes, lateral shifts, and chokers are all curb extensions installed away from an intersection to create a narrow two-lane gap or a single lane. Chicanes shift traffic alternately from side to side of the street to create an S-shaped path of travel. Lateral shifts are curb extensions that cause travel lanes to bend one way and then back the other way. Chokers are midblock curb extensions that narrow the street by expanding the sidewalk or adding a planting strip and often are installed at midblock crossings.
Figure 9-21. Curb extensions at medians should include low landscaping to clarify the path of travel for pedestrians with vision impairments. High landscaping would block sight lines for motorists and pedestrians.
In general, chicanes, lateral shifts, and chokers have positive impacts on pedestrian access. When designed as curb extensions, chokers reduce pedestrian crossing distances and enhance pedestrian visibility when installed at midblock crossings.
The following recommendations are intended to enhance access at chicanes, lateral shifts, and chokers:
Curb extensions at intersections are installed to reduce the roadway width from curb to curb at an intersection. Other names for curb extensions include neckdowns and bulbouts.
Curb extensions at intersections are the most common type of street narrowing and are primarily used to make intersections more pedestrian friendly. Curb extensions benefit pedestrians by creating shorter crossing distances, increased pedestrian visibility, and tighter curb radii that reduce the speeds of turning vehicles. On existing narrow sidewalks, curb extensions can provide an area necessary for curb ramps.
The following recommendations are intended to enhance access at curb extensions:
Center island narrowings are raised islands located at the centerline of a street. Other names for center island narrowings include midblock medians, median slow points, or median chokers. Travel speeds are reduced due to the narrow path of travel at that location and are particularly effective on curves. Center islands also act as effective pedestrian refuge locations.
Center island narrowings have the following positive impacts on access:
The following recommendations are intended to enhance access at center island narrowings: