Have you ever been stuck in bumper-to-bumper traffic and then with no apparent reason the traffic just starts moving again at 60 mph? A team of mathematicians from the Universities of Exeter, Bristol and Budapest published the reason why in the journal Proceedings of the Royal Society.
Something as simple as a slow truck moving into a different lane on a busy highway - defined as more than 25 vehicles per mile, or one every 200 feet - can cause a ripple effect called a backward traveling wave.
University of Exeter Dr. Gábor Orosz said, "When you tap your brake, the traffic may come to a full stand-still several miles behind you. It really matters how hard you brake - a slight braking from a driver who has identified a problem early will allow the traffic flow to remain smooth. Heavier braking, usually caused by a driver reacting late to a problem, can affect traffic flow for many miles."
Just great. Now we can ruin hundreds of people's day just by braking too late on the highway.