Gridlock is a term which is used to refer to the stagnation of a transportation system through the blockage of key intersections. The term is also used more generally to talk about stagnated movements in other fields as well, hence the term “legislative gridlock.” Since progress is impossible during gridlock, it is an undesired condition. As a result, transit engineers work very hard to reduce the probability of gridlock in a number of ways.
The term is usually used specifically to refer to automobile traffic, although gridlock can also occur in narrow sea lanes and along train tracks. However, traffic provides a particularly visual illustration of gridlock, since it often involves huge numbers of cars, and it can take hours to clear the snarls of a gridlocked traffic jam. Due to human nature, gridlock is often severely exacerbated by human actions, usually when people fail to cooperate on solving the problem.
The term was used by public authorities in New York City as early as the 1970s, and it became more widely popularized due to a 1980 New York Times Magazine article. The term quickly caught on, because it is highly illustrative, and because gridlocked traffic started to become a very severe problem in the United States in the 1980s. Once the term entered popular usage, it also started diverging in meaning.
In order to be truly considered gridlock, a traffic jam must be caused by blocked intersections. Traffic intersections represent a major vulnerability in the smooth flow of traffic, since drivers often behave in unpredictable ways in intersections. Once cross traffic starts to build up in an intersection, no one can go anywhere, resulting in blockages which spill over into the surrounding street grid, essentially locking it so that no one can pass.
In many regions of the world, it is illegal to block an intersection for this very reason. Unfortunately, frustrated or arrogant drivers often do so anyway, in the hopes that they will get ahead. When multiple drivers engage in the practice, the problem can get quite severe. Many drivers model their behavior after others, so once one car stops in an intersection, others will follow.
To address gridlock, engineers try to create smooth transit systems. They anticipate problem intersections and make an effort to create more options for drivers. In addition, they may program streetlights to promote the flow of traffic. More innovative programs like encouraging employers to allow people to work staggered shifts to reduce the rush hour crunch common in many cities also began growing in popularity in the late 1990s. With a growing number of cars on the road, adding more streets and aggressively ticketing people who contribute to the problem are also important ways to fight gridlock.