Gridlock is a situation where road congestion becomes so bad that traffic grinds to a complete halt for hours or days at a time, upsetting Commuters and Motorists, making some Motorists give up their hobby, and causing a drop in the GDP.
Gridlock occurs when a nation's Car Usage exceeds 93%. Getting people to cut down on car usage is one of the easiest ways of alleviating the situation but enacting Satellite Road Pricing can also help fix all but the worst cases of gridlock too.