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, backing up to an upstream intersection, as illustrated below.

      |  V   |           | ^  |
----    V   --------      ---------
         V   <<<<<<<<<<<<<
----   V    ------       ---------
       | V   |           | ^  |
       | V   |           | ^  |
       | V   |           | ^  |
       | V   |           | ^  |
----   V      -------  ^       ---------
   >>>>>>>>>>     ^
----   V      -------  ^       ---------
       |  V   |           | ^  |

Most jurisdictions have legislation prohibiting drivers 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.