Gridlock

Gridlock is a term describing an inability to move on a transport network. The term originates from a situation possible in a grid network where intersections are blocked, prohibiting vehicles from moving through the intersection or backing up to an upstream intersection.

The term "gridlock" is also widely used to describe high traffic congestion with minimal flow (a "traffic jam"), whether or not a blocked grid system is involved. By extension, the term has been applied to situations in other fields where flow is stalled by excess demand, or in which competing interests prevent progress.

Cause

The traditional form of gridlock is caused by traffic heading in one direction blocking cross traffic at an intersection. In many jurisdictions, drivers are prohibited from entering an intersection if they cannot clear it before the traffic light turns red. If drivers follow this rule of the road, gridlock will be prevented and traffic will only be slow in the direction that is actually congested. One method of reducing gridlock is to aggressively enforce penalties for vehicles that block intersections. [Stringer, Scott M. " [http://beta.mbpo.org/press/pressreleases/file.2006-07-11.7527366504 Thinking outside the box: an analysis of Manhattan gridlock and spillback enforcement] ", Office of Manhattan Borough President, July 2006.]

Another type of gridlock can occur during traffic surges between highway on-ramps and off-ramps located within a quarter mile of each other. Traffic exiting the highway may back up and block the entering vehicles. Gridlock is sometimes cited as an example of the prisoner's dilemma (from game theory). [Heath, Joseph (1999). " [http://www.utm.utoronto.ca/~w3phl296/text/table.html Normative economics] ", Chapter 2, Section 3. Retrieved on March 19 2007.] Mutual cooperation among drivers would give the maximum benefit (prevention of gridlock), but this may not happen because of the desire to maximize one's own benefit (shortest travel time) given the uncertainty about the other drivers' commitment to cooperation.

Enforcement

New York City

In New York City, drivers who "block the box" are subject to a moving violation that comes with a US$90.00 penalty. Mayor Michael Bloomberg, noting that the ten minute ticketing process actually contributes to overall traffic congestion, has recently asked the New York State Legislature to remove “blocking the box” from the moving violation category. This reclassification would give more traffic agents authority to write tickets and change the current ticketing procedure, which requires that the issuing officer physically stop the violating car in traffic. [ [http://ny.metro.us/metro/local/article/Bloomberg_crackdown_on_gridlock_/8745.html metro ] ]

Effects

The obvious impacts are driver frustration and trip delay. Another impact in cities is exacerbated by the presence of urban street canyons, which effectively trap air pollution and increase air pollution exposures of motorists as well as the general urban population. Noise pollution can be aggravated by excessive starting and stopping noise of gridlocked facilities. [" [http://www.worldcatlibraries.org/wcpa/top3mset/2930880 C. Michael Hogan and Gary L. Latshaw, The relationship between highway planning and urban noise] ", :Proceedings of the ASCE, Urban Transportation Division specialty conference, May 21-23, 1973, Chicago, Illinois. by American Society of Civil Engineers. Urban Transportation Division]

Etymology

The first appearances of the word "gridlock" in newspapers occurred in 1980, during a transit strike in New York City. The word is attributed to Sam Schwartz, who was the chief traffic engineer for the city's Department of Transportation at the time of the strike. [Schwartz, Sam. " [http://www.gridlocksam.com/about.html About Gridlock Sam] ", GridlockSam.com. Retrieved on March 19 2007.] Schwartz said the word "gridlock" was used internally in his department during the 1970s, perhaps as early as 1971. [Popik, Barry (July 21, 2004). " [http://www.barrypopik.com/index.php/new_york_city/entry/gridlock/ Gridlock] ". Retrieved March 19 2007.]

ee also

*Box junction
*Deadlock - computer software analogy
*Roadway air dispersion modeling

References