00:00you're on the highway and everything stops you crawl for 10 minutes then it just clears no crash
00:06no road work nothing so what stopped you in 2008 researchers in japan tried to make a jam out of
00:13nothing they put 22 cars on a circular track with one rule hold a steady 19 miles an hour
00:20no exits no merges and a jam showed up anyway it starts with one driver tapping the brakes
00:26the driver behind takes about a second to notice by then the gap has shrunk so they break a bit
00:32harder and the next driver breaks harder still the slowdown grows with every car until someone
00:38has to stop completely and here's the weird part the jam moves backward cars leave it at the front
00:44and new cars join at the back so the jam itself drifts against traffic at around 10 miles an hour
00:50it can roll back for miles long after whoever started it is gone that's why when you reach
00:56the front there's nothing there it's a phantom jam but why doesn't this happen on an empty road
01:01because a gap is a buffer with room to spare the driver behind just eases off and the slowdown fades
01:08but once cars are packed in tight there's no room to soak it up so every little tap grows into
01:14a jam so
01:15how do you stop one in 2017 researchers in arizona put one self-driving car into a ring of about
01:2220
01:22human drivers it didn't chase the car in front it just held a steady pace and left itself room
01:28and that one car calmed the whole ring hard braking almost disappeared and fuel use fell by up to 40
01:36so drive like that car leave a bigger gap and ease off early instead of braking hard
01:42you won't get there much faster but the cars behind you might never have to stop
