A traffic jam in which no vehicular movement is possible, especially one caused by the blockage of key intersections within a grid of streets.
A complete lack of movement or progress resulting in a backup or stagnation:
"the political gridlock that prevented ... the President and Congress from moving expeditiously to cut the budget"
(Robert D. Hormats).
OTHER FORMS:
gridlock(Verb),
gridlocked(Adjective)