Cause
The traditional form of gridlock is caused by traffic heading in one direction across an intersection. This traffic is then stopped, by sometimes too much capacity for the roadway or an accident, blocking the intersection. The drivers in the other direction then go into the blocked intersection trying to get through. In many jurisdictions, drivers are prohibited from entering an intersection at a green light if there is no room for them to clear the intersection. 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.
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). 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.
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