Extensions | Choker
Curb extensions - also known as bulb-outs or neckdowns - extend the sidewalk or curb line out into the parking lane, which reduces the effective street width. Curb extensions significantly improve pedestrian crossings by reducing the pedestrian crossing distance, improving the ability of pedestrians and motorists to see each other, and reducing the time that pedestrians are in the street.
Curb extensions placed at an intersection essentially prevent motorists from parking in or to close to a crosswalk or from blocking a curb ramp. Motor vehicles parked at corners present a threat to pedestrian safety, as they block sight lines, obscure visibility of pedestrians and other vehicles, and make turning particularly difficult for emergency vehicles and trucks. Motorists are encouraged to travel more slowly at intersections or midblock locations with curb extensions, as the restricted street width sends a visual cue to motorists. Turning speeds at intersections are reduced with curb extensions (curb radii should be as tight as is practicable).
Curb extensions are only appropriate where there is an on-street parking lane. Curb extensions must not extend into travel lanes, bicycle lanes or shoulders). The turning needs of larger vehicles such as school buses need to be considered in curb extension design.
A curb extension on an arterial street in
Seattle, Washington. The crossing distance for pedestrians is substantially
reduced by the installation of this device.
A curb extension on a residential street,
also in Seattle, Washington. In addition to improving pedestrian
safety at this intersection, the bulb provides additional sidewalk
space for a bicycle rack.
The material provided on this page is from the FHWA publication
"Pedestrian Facilities User Guide." This guide is currently under review
by practicioners and others in the field. Subsequently, the material
provided on this page is subject to change in the future.
Improves safety for pedestrians and motorists at intersections;
increases visibility and reduces speed of turning vehicles.
Encourages pedestrians to cross at designated locations.
Prevents motor vehicles from parking at corners.
Curb extensions should typically be used where there is a parking
lane, and where transit and cyclists would be traveling outside the
curb edge for the length of the street.
Midblock extensions provide an opportunity to enhance midblock
crossings. Care should be taken to insure that street furniture and
landscaping do not block motoristsí views of pedestrians.
Where intersections are used by significant numbers of trucks
or buses, the curb extensions need to be designed to accommodate them.
However, it is important to take into consideration that those vehicles
should not be going at high speeds, and most can make a tight turn
at slow speeds. It is also not always necessary for a roadway to be
designed so that a vehicle be expected to turn from right lane to
right lane - i.e., the vehicles can often encroach into adjacent lanes
safely where volumes and/or speeds are slow. Keep in mind that speeds
should be slower in a pedestrian environment.
Emergency access is often improved through the use of curb
extensions, as intersections are kept clear of parked cars. Fire engines
and other emergency vehicles can climb a curb where they would not
be able to move a parked car. In addition, at mid-block locations,
curb extensions can keep fire hydrants clear of parked cars and make
them more accessible.
Curb extensions can be used to place landscaping and street
furniture; this is especially beneficial where sidewalks are otherwise
Curb extensions cost from $2,000 to $20,000 per corner, depending
on design and site conditions. Drainage is usually the most significant
determinant of costs. If the curb extension area is large and special
pavement and street furnishings and planting are included, costs would
also be higher. Costs can go up significantly if something major such
as a mast arm or controller box is moved.