Traffic Diverters


Traffic diverters are raised islands or channelization devices that prevent drivers from making particular turns or through moves, usually on residential streets plagued with "cut-through" traffic. For example, a traffic diverter may be installed which forces all traffic at a particular intersection to turn left or turn right. Breaks in the middle of the diverter are commonly provided to allow pedestrians and bicyclists to pass through the diverter.

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Types of Diverters

The four types of intersection diverters are the diagonal (pictured), star, forced turn, and truncated. A star diverter is a star-shaped raised island placed in the middle of a residential intersection, which forces cars approaching from all directions to turn right. A truncated diagonal diverter, as known as a semi-diverter[1], keeps one end open to allow some turning movements while preventing others. Other types of diverters are placed on one or more approaches to prevent through and left-turn movements. Diverters are employed in the installation of a bicycle boulevard .

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Other kinds of diverters include median barriers, full street closures, and half-closures. These restrict traffic in ways similar to the intersection-based diverters. Often, median barriers are installed to prevent left turns in and out of a residential street from an arterial street, in order to reduce crashes associated with these turns. Breaks may be included in the median to allow bicyclists or emergency vehicles to pass through (pictured).

Signals, signs, or street legends (markings) can also be used to divert traffic. The most typical example is a signal or sign where one of the approaches requires motorists to turn left or right. Bicyclists and pedestrians are generally allowed to make the through movement.

What to Consider

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A temporary diverter (pictured) can be set up quickly and inexpensively. This is often a good idea to test the concept, but residents should be made aware the permanent installation will be far more attractive. Permanent intallations of a traffic diverter may cost form $15,000 to $100,000[2], and should be considered only when less restrictive measures are not feasible. Emergency responders generally dislike diverters since they require additional time, or additional planning, to reach homes on the other side of the diverter as quickly as possible. Another important consideration when installing a traffic diverter is the impact it will have on the circulation patterns within the neighborhood. The diverted traffic will be using other neighborhood streets, or may stay on arterial streets and avoid the neighborhood streets altogether -- the best outcome. As with any traffic calming installation, the installation should be revisited after 6 months or a year, and adjustments or additional devices installed as needed to achieve the neighborhood's and city's goals.

ALSO ON THE LIVABLE STREETS NETWORK


REFERENCES

Each source is referred to by the same number every time it is cited. Please keep citation style consistent.
[1] Reduce Traffic Volume. City of Portland Department of Transportation.
[2] Diverters, Walkinginfo.org, Pedestrian Bicycle Information Center.
[3]
[4]

PICTURE REFERENCES

Pictures are cited in the order they appear above. Please keep citation style consistent.
[1] Diagonal diverter. Photo by Dan Burden.
[2] Street closure as temporary diverter. Phtoto by Andy Hamilton (unpublished).
[3] Median barrier with emergency vehicle passage. Photo by Dan Burden via Pedestrian Bicycle Information Center Image Library.

FURTHER READING


KEYWORDS

diverter, traffic calming, diagonal diverter, star diverter, semi-diverter, street closure, median barrier