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Vehicle speed is the single most important indicator of the safety of a street. The higher the speed, the higher the crash rate and the injury severity rate. As such, it is imperative to manage vehicle speeds. Introducing high speeds into narrow, constrained corridors may cause traffic injuries and fatalities. While traffic enforcement can help manage speeds, it is not always available. Instead, speed management should be achieved through design complemented by intersection controls and supported by enforcement where possible.
Speed management lowers the likelihood of severe or fatal traffic injuries by reducing the frequency and severity of crashes. For pedestrians, speed management creates safe conditions for crossing, walking along the corridor, or sharing space with cycle or motor vehicle traffic. For cyclists, lower speed reduces the number of overtaking events, improves visibility and reaction time, and greatly reduces the severity of crashes that do occur.
Low and consistent traffic speed decreases noise and air pollution that result from acceleration and deceleration, while reducing stress for vulnerable road users.
Highway design is very limited, but as speed is lowered, the design palette expands. Speed management strategies include cost-effective, readily implemented techniques for streets of every size, traffic volume level, context, and human activity level.
Geometric Traffic Calming Strategies
Reduce speeding by introducing vertical elements such as speed bumps or raised pedestrian crossings, and horizontal elements like curb extensions, pedestrian refuge islands, or lane narrowing, into the streetscape. Comprehensive design techniques use visual and other sensory inputs to signal to drivers that they are entering an interactive, multimodal space, rather than a traffic-only space.
Combining multiple speed reduction treatments, slow zones, also known as limited-speed zones or home zones, can be implemented in areas with lower speed limits than the rest of the city, such as around schools or residential areas. These should be identified with self-enforcing gateway treatments and signs to alert drivers to the reduced speed limit. See: Designing for Pedestrians.
Roadway and Lane Narrowing
Narrowing lanes and reducing the total amount of space available to vehicles reduces speeding. On one-way streets, excess road width can be repurposed for pedestrian, cycle, and transit facilities. In places with lower traffic volumes, conversion to two-way streets can lower speeds and improve driver attention by requiring negotiation with oncoming traffic.
When set to cycle- and transitfriendly speeds of 20–25 km/h, signal progressions can remove much of the incentive to speed. This tool can be applied inexpensively and effectively on almost any signalized street regardless of size, and is especially easy to implement on one-way streets.
Set Speeds to Human Limits
The combination of speed and conflict produces deadly results. The human body’s limit to withstand impacts is the critical design parameter for urban streets. Safe walking and cycling require motor vehicle speeds to be set at survivable levels. The systematic way to eliminate fatalities is to eliminate highspeed interactions by:
Survivability of a crash is much better below 30 km/h. Younger and older users and conflicts with larger vehicles require even lower speeds. For the most vulnerable users and for heavy vehicles, there might be no survivable impact speed.
Reduce turning speeds at pedestrian crossings to 10 km/h, and drop top speeds to 30 km/h where cycles share a lane with motor vehicles. On streets where the interaction between people and motor vehicles is limited to frequent controlled crossings, speeds of 40 km/h can be permitted.
Rather than designing streets for speeds higher than the speed limit, target speeds should be set low enough that even non-compliant drivers will present minimal risk to pedestrians.
All streets must be easy to cross and should be designed to encourage safe crossings. Planned crossing locations must be frequent to account for the time spent by people walking to a crossing. On multi-lane streets, reduce the distances between crossing points, and reduce the distance (number of lanes) between pedestrian refuges, especially on streets that lack traffic controls.
Legibility and Uniformity
Safe streets can be read by their users—geometry, materials, and roadway markings communicate critical information, including appropriate speeds and where to expect other people and vehicles.
Reduced speeds expand the use of peripheral vision by drivers, widening the visual cone and increasing the chance of seeing people crossing.
Organize Large Streets, Share Small Streets
Large streets call for dedicated space for each user. On small streets or intersections with very low speeds, people can mix with vehicles safely. The appropriate tools of traffic operations and geometric design should be applied, depending on the level of connectivity and traffic volume on the street.
Accessible Streets are Safe Streets
Streets must provide accessible paths that meet the fundamental movement needs of all users, especially pedestrians in wheelchairs, the visually impaired, and people with strollers or baby prams. Inaccessible streets force the most vulnerable users into unsafe conditions.
Adapted by Global Street Design Guide published by Island Press.
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