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Gridlock
Gridlock is used to describe traffic congestion; when vehicles are unable to move on a transportation network. The term was coined in 1980 by Sam Schwartz ("
Gridlock Sam
"), then a deputy traffic commissioner at the
New York City Department of Transportation
. The term "gridlock" comes from the literal description of an intersection within a street grid system in which traffic backed up in one direction blocks cross traffic from entering the intersection when given a green light. Under these conditions, a roadway is said to have a "Level of Service" F, where A is free-flowing and F is standstill traffic.
Ironically, grid systems are the single most efficient way to distribute traffic and avoid congestion. For this reason, the grid street pattern found in many traditional downtown areas of large cities do not exhibit gridlock, whereas lengthy delays are experienced routinely in suburban areas in which all traffic is funneled onto a few large arterial streets or interstate highways.
Antidotes to Gridlock
Cities have attempted to combat gridlock in the short term in two ways: through pricing incentives/disincentives, and by making it a moving traffic violation to enter an intersection when the road ahead is filled with vehicles. New York City found that officers issuing tickets to offending drivers caused still more congestion, and have sought other ways to carry out enforcement. In 2009, the city was considering free transit as a way to relieve peak congestion[1].
Another method has been to institute Demand Management programs that induce commuters to make more of their trips at off-peak hours, or to work from home (telecommute). Less direct measures include price signals, such as
Congestion Pricing
or higher parking charges at times of high demand.
In the longer term, cities generally address congestion Dby increasing roadway capacity. This can be done by physically expanding the pavement, adding lanes, especially dedicated turn lanes. Another method is to convert two-way streets to one-way, either permanently or only during periods of high demand such as commute times or for special events. Still another method is to coordinate signals so that vehicles traveling a particular speed find a green light at each intersection in a corridor. This is known as signal synchronization. Finally, intersection efficiency improvements such as replacing traffic signals with roundabouts (photo) can increase thru-put, avoiding delays.
Long-Term Congestion Relief
Ultimately, the long-term solution to reducing gridlock (congestion) is to reduce the number of vehicle trips on the system. This can be done by expanding other options and dampening demand for more vehicle travel. The options can be summarized as follows:
We now recognise the need to reinvent safe, attractive streets in which it is normal for children to walk or cycle to school; to reinvent the old custom of home delivery of shopping; to rediscover the role of land-use planning to reduce journey distances; to look for ways of participating in social activities that generate less traffic. The new policy tool-box includes pedestrianisation, traffic calming, traffic management aimed at maintaining a quality margin of reliability by reducing flows to significantly less than capacity; and once again pricing is everywhere discussed, as the only tool of traffic restraint which has the double whammy of ensuring that resource costs are covered in the choices people make, and also providing the funds to pay for improvements[2].
For example, both
Portland, Oregon
, and Vancouver, BC, Canada, have experienced reduced congestion by improving transit, pedestrian, and bicycling networks and ensuring there is a good mix of land uses so destinations are conveniently close by.
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] See "Also On the Livable Streets Network".
[2] Goodwin, P.B. 1997. Solving congestion (when we must not build roads, increase spending, lose votes, damage the economy or harm the environment, and will never find equilibrium). Inaugural lecture for the Professorship of Transport Policy University College London.
[3]
[4]
PICTURE REFERENCES
Pictures are cited in the order they appear above. Please keep citation style consistent.
[1] Gridlock diagram. Graphic via Wikimedia.
[2] Do Not Block Intersection sign Manual of Uniform Traffic Control Devices
[3] Roundabout, La Jolla Blvd., San Diego, CA. Photo by Dan Burden via Pedestrian Bicycle Information Center Image Library.
FURTHER READING
KEYWORDS
Induced traffic, Level of Service, congestion, Portland, Vancouver
