Originally Posted by banerjek
True, but on a crowded 4 lane highway, slowing down one person in the fast lane can change the pace of the entire line for a surprisingly long time because of the "slinky" effect in dense traffic. The slinky effect often forces drivers to slow to a crawl or even stop hours after an accident has been cleared even though the level of traffic is only moderately high.
Absolutely true and exploited by law enforcement in Alberta. The RCMP regularly parks empty cruisers along stretches of highway that are deemed dangerous because of conditions or heavy traffic (used frequently on the road between Banff and Lake Louise). They turn on the radar and leave it on. On a two lane highway it slows traffic down for miles in both directions.