Road Sign from the China National Highway 110 Traffic Jam

Origin
Possibly the worst traffic jam in history occurred mid-August 2010 on China National Highway 110 and the Beijing-Tibet Expressway. Overcongestion, accidents and construction compounded together and slowed down thousands of vehicles for more than 100 kilometers (60 mi). It lasted for more than ten days, and some drivers reported being stuck in the traffic jam for five days. Many locals took to selling goods like bottled water and cigarettes at hyper-inflated prices to stranded drivers, creating a miniature road economy.

Effects
The road sign has the ability to make any existing traffic jam worse. Vehicles will suddenly start flocking onto the major roads, accidents will occur and average driver skill level will drop. It also has a desire to continue them for as long as possible, which can lead to impasses days long.