Chicanes, as the term is used here, create a serpentine, horizontal shifting of travel lanes, without reducing the number of lanes or lane width, by alternating curb extensions from one side of the roadway to the other. Shifting a travel lane has an effect on travel speeds by interrupting straight stretches of roadway and forcing vehicles to shift laterally. Chicanes must be well designed so that the taper is not so gradual that motorists can maintain speeds through the curve or by cutting a shortcut path across the center line. For traffic calming, the taper lengths may be as much as half of what is suggested in traditional highway engineering. According to Ewing2, "European design manuals recommend shifts in alignment of at least one lane width, deflection angles of at least 45 degrees, and center islands to prevent drivers from taking a straight ‘racing line’ through the feature."
Shifts in travel-ways can be created by building landscaped islands or extended walkways, or less expensively, by shifting parallel or angled parking from one side of the roadway to the other. Landscaped bulb-outs or expanded walkways can also effectively enclose parking bays and supplement the parking shift. If there is no restriction or narrowing (i.e., the number and width of lanes is maintained), chicanes can be created on streets with higher volumes, such as collectors or minor arterials, as well as on neighborhood streets.
A new or re-constructed roadway could also be designed in a serpentine fashion to keep sight lines short and force vehicles to make lateral shifts. Such a design could even be used where there is no curb such as in parks or rural areas where the scenic qualities also would support such a design.
Diverting the path of travel plus restricting the lanes (often called "chokers")
usually consists of a series of midblock curb extensions, narrowing the street
to two narrow lanes or one lane at selected points and forcing motorists to
slow down to maneuver between them. Chokers or lateral shifts that create pinch
points or reduce the number of lanes, which may be accomplished through the
addition of landscaped islands or sidewalk bulb-outs, are intended for use
only on local streets with low traffic volumes. Chokers may be used to simultaneously
create a narrowed pedestrian crossing zone. Use of chokers should be carefully
evaluated to avoid creating potential conflict zones between overtaking motorists
- Reduce vehicle speeds by interrupting straight stretches of roadway.
- Add more green (landscaping) to a street.
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- Chicanes may sometimes be used on minor arterial streets, but should not be used on high-speed, high-volume arterials.
- Chicanes may reduce on-street parking.
- Maintain good visibility by planting only low shrubs or trees with high canopies.
- Ensure that bicyclist safety and mobility are not diminished.
- Effect of chokers (with narrowing or lane restrictions) on bicyclists should be carefully evaluated prior to implementation; use should typically be restricted to lower-volume local streets to prevent bicyclist-motorist conflicts at pinch points. Chokers should not be used on streets heavily used by bicycles (or with bike lanes) unless design provides for bicyclist accommodation.
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Costs for landscaped chicanes are approximately $10,000 (for a set of three chicanes) on an asphalt street and $15,000 to $30,000 on a concrete street. Costs should be far less for chicane-like parking configuration. Costs for chokers are estimated at $5,000 to $20,000. Drainage and utility relocation often represent the most significant cost consideration.
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