[Script Info] Title: [Events] Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text Dialogue: 0,0:00:06.90,0:00:09.43,Default,,0000,0000,0000,,You’re cruising down the highway \Nwhen all of a sudden Dialogue: 0,0:00:09.43,0:00:12.35,Default,,0000,0000,0000,,endless rows of brake lights appear ahead. Dialogue: 0,0:00:12.35,0:00:14.59,Default,,0000,0000,0000,,There’s no accident, no stoplight, Dialogue: 0,0:00:14.59,0:00:17.52,Default,,0000,0000,0000,,no change in speed limit \Nor narrowing of the road. Dialogue: 0,0:00:17.52,0:00:21.01,Default,,0000,0000,0000,,So why the @#$%! is there \Nso much traffic? Dialogue: 0,0:00:21.01,0:00:24.59,Default,,0000,0000,0000,,When traffic comes to a near standstill \Nfor no apparent reason, Dialogue: 0,0:00:24.59,0:00:27.52,Default,,0000,0000,0000,,it’s called a phantom traffic jam. Dialogue: 0,0:00:27.52,0:00:30.42,Default,,0000,0000,0000,,A phantom traffic jam \Nis an emergent phenomenon Dialogue: 0,0:00:30.42,0:00:35.02,Default,,0000,0000,0000,,whose behavior takes on a life of its own,\Ngreater than the sum of its parts. Dialogue: 0,0:00:35.02,0:00:38.65,Default,,0000,0000,0000,,But in spite of this, \Nwe can actually model these jams, Dialogue: 0,0:00:38.65,0:00:41.24,Default,,0000,0000,0000,,even understand the principles \Nthat shape them— Dialogue: 0,0:00:41.24,0:00:43.04,Default,,0000,0000,0000,,and we’re closer than you might think Dialogue: 0,0:00:43.04,0:00:46.20,Default,,0000,0000,0000,,to preventing this kind of traffic\Nin the future. Dialogue: 0,0:00:46.20,0:00:51.09,Default,,0000,0000,0000,,For a phantom traffic jam to form, \Nthere must be a lot of cars on the road. Dialogue: 0,0:00:51.09,0:00:54.21,Default,,0000,0000,0000,,That doesn’t mean \Nthere are necessarily too many cars Dialogue: 0,0:00:54.21,0:00:56.54,Default,,0000,0000,0000,,to pass through a stretch \Nof roadway smoothly, Dialogue: 0,0:00:56.54,0:01:01.12,Default,,0000,0000,0000,,at least not if every driver maintains \Nthe same consistent speed and spacing Dialogue: 0,0:01:01.12,0:01:02.56,Default,,0000,0000,0000,,from other drivers. Dialogue: 0,0:01:02.56,0:01:04.98,Default,,0000,0000,0000,,In this dense, but flowing, traffic, Dialogue: 0,0:01:04.98,0:01:09.41,Default,,0000,0000,0000,,it only takes a minor disturbance \Nto set off the chain of events Dialogue: 0,0:01:09.41,0:01:11.64,Default,,0000,0000,0000,,that causes a traffic jam. Dialogue: 0,0:01:11.64,0:01:14.08,Default,,0000,0000,0000,,Say one driver brakes slightly. Dialogue: 0,0:01:14.08,0:01:18.40,Default,,0000,0000,0000,,Each successive driver then brakes \Na little more strongly, Dialogue: 0,0:01:18.40,0:01:21.84,Default,,0000,0000,0000,,creating a wave of brake lights \Nthat propagates backward Dialogue: 0,0:01:21.84,0:01:23.52,Default,,0000,0000,0000,,through the cars on the road. Dialogue: 0,0:01:23.52,0:01:28.51,Default,,0000,0000,0000,,These stop-and-go waves \Ncan travel along a highway for miles. Dialogue: 0,0:01:28.51,0:01:31.05,Default,,0000,0000,0000,,With a low density of cars on the road, Dialogue: 0,0:01:31.05,0:01:34.08,Default,,0000,0000,0000,,traffic flows smoothly \Nbecause small disturbances, Dialogue: 0,0:01:34.08,0:01:38.45,Default,,0000,0000,0000,,like individual cars changing lanes \Nor slowing down at a curve, Dialogue: 0,0:01:38.45,0:01:41.27,Default,,0000,0000,0000,,are absorbed by other \Ndrivers’ adjustments. Dialogue: 0,0:01:41.27,0:01:45.60,Default,,0000,0000,0000,,But once the number of cars \Non the road exceeds a critical density, Dialogue: 0,0:01:45.60,0:01:50.03,Default,,0000,0000,0000,,generally when cars are spaced \Nless than 35 meters apart, Dialogue: 0,0:01:50.03,0:01:53.32,Default,,0000,0000,0000,,the system’s behavior \Nchanges dramatically. Dialogue: 0,0:01:53.32,0:01:59.66,Default,,0000,0000,0000,,It begins to display dynamic instability, \Nmeaning small disturbances are amplified. Dialogue: 0,0:01:59.66,0:02:03.66,Default,,0000,0000,0000,,Dynamic instability isn’t unique \Nto phantom traffic jams— Dialogue: 0,0:02:03.66,0:02:10.05,Default,,0000,0000,0000,,it’s also responsible for raindrops, \Nsand dunes, cloud patterns, and more. Dialogue: 0,0:02:10.05,0:02:13.33,Default,,0000,0000,0000,,The instability is \Na positive feedback loop. Dialogue: 0,0:02:13.33,0:02:15.02,Default,,0000,0000,0000,,Above the critical density, Dialogue: 0,0:02:15.02,0:02:19.38,Default,,0000,0000,0000,,any additional vehicle reduces \Nthe number of cars per second Dialogue: 0,0:02:19.38,0:02:22.16,Default,,0000,0000,0000,,passing through a given point on the road. Dialogue: 0,0:02:22.16,0:02:26.21,Default,,0000,0000,0000,,This in turn means it takes longer \Nfor a local pileup Dialogue: 0,0:02:26.21,0:02:31.08,Default,,0000,0000,0000,,to move out of a section of the road, \Nincreasing vehicle density even more, Dialogue: 0,0:02:31.08,0:02:35.19,Default,,0000,0000,0000,,which eventually adds up \Nto stop-and-go traffic. Dialogue: 0,0:02:35.19,0:02:40.25,Default,,0000,0000,0000,,Drivers tend not to realize they need \Nto break far in advance of a traffic jam, Dialogue: 0,0:02:40.25,0:02:44.43,Default,,0000,0000,0000,,which means they end up having \Nto brake harder to avoid a collision. Dialogue: 0,0:02:44.43,0:02:48.70,Default,,0000,0000,0000,,This strengthens the wave of braking \Nfrom vehicle to vehicle. Dialogue: 0,0:02:48.70,0:02:53.37,Default,,0000,0000,0000,,What’s more, drivers tend to accelerate\Ntoo rapidly out of a slowdown, Dialogue: 0,0:02:53.37,0:02:55.07,Default,,0000,0000,0000,,meaning they try to drive faster Dialogue: 0,0:02:55.07,0:02:58.19,Default,,0000,0000,0000,,than the average flow of traffic \Ndownstream of them. Dialogue: 0,0:02:58.19,0:03:02.71,Default,,0000,0000,0000,,Then, they have to brake again, \Neventually producing another feedback loop Dialogue: 0,0:03:02.71,0:03:05.81,Default,,0000,0000,0000,,that causes more stop-and-go traffic. Dialogue: 0,0:03:05.81,0:03:09.22,Default,,0000,0000,0000,,In both cases, drivers make traffic worse Dialogue: 0,0:03:09.22,0:03:13.50,Default,,0000,0000,0000,,simply because they don’t have a good\Nsense of the conditions ahead of them. Dialogue: 0,0:03:13.50,0:03:18.02,Default,,0000,0000,0000,,Self driving cars equipped with data \Non traffic conditions ahead Dialogue: 0,0:03:18.02,0:03:21.06,Default,,0000,0000,0000,,from connected vehicles \Nor roadway sensors Dialogue: 0,0:03:21.06,0:03:24.58,Default,,0000,0000,0000,,might be able to counteract \Nphantom traffic in real-time. Dialogue: 0,0:03:24.58,0:03:29.06,Default,,0000,0000,0000,,These vehicles would maintain \Na uniform speed, safety permitting, Dialogue: 0,0:03:29.06,0:03:32.79,Default,,0000,0000,0000,,that matches the average speed \Nof the overall flow, Dialogue: 0,0:03:32.79,0:03:35.41,Default,,0000,0000,0000,,preventing traffic waves from forming. Dialogue: 0,0:03:35.41,0:03:38.22,Default,,0000,0000,0000,,In situations where there’s \Nalready a traffic wave, Dialogue: 0,0:03:38.22,0:03:41.72,Default,,0000,0000,0000,,the automated vehicle \Nwould be able to anticipate it, Dialogue: 0,0:03:41.72,0:03:44.90,Default,,0000,0000,0000,,braking sooner and more gradually \Nthan a human driver Dialogue: 0,0:03:44.90,0:03:47.98,Default,,0000,0000,0000,,and reducing the strength of the wave. Dialogue: 0,0:03:47.98,0:03:51.20,Default,,0000,0000,0000,,And it wouldn’t take that many \Nself-driving cars— Dialogue: 0,0:03:51.20,0:03:56.87,Default,,0000,0000,0000,,In a recent experiment, one autonomous \Nvehicle for every 20 human drivers Dialogue: 0,0:03:56.87,0:04:00.24,Default,,0000,0000,0000,,was enough to dampen \Nand prevent traffic waves. Dialogue: 0,0:04:00.24,0:04:03.25,Default,,0000,0000,0000,,Traffic jams are not only \Na daily annoyance– Dialogue: 0,0:04:03.25,0:04:05.48,Default,,0000,0000,0000,,they’re a major cause of fatalities, Dialogue: 0,0:04:05.48,0:04:09.24,Default,,0000,0000,0000,,wasted resources, \Nand planet-threatening pollution. Dialogue: 0,0:04:09.24,0:04:12.48,Default,,0000,0000,0000,,But new technology may help reduce \Nthese patterns, Dialogue: 0,0:04:12.48,0:04:14.19,Default,,0000,0000,0000,,rendering our roads safer, Dialogue: 0,0:04:14.19,0:04:18.01,Default,,0000,0000,0000,,our daily commutes more efficient, \Nand our air cleaner. Dialogue: 0,0:04:18.01,0:04:20.13,Default,,0000,0000,0000,,And the next time you’re stuck in traffic, Dialogue: 0,0:04:20.13,0:04:24.91,Default,,0000,0000,0000,,it may help to remember that other drivers\Naren’t necessarily driving spitefully, Dialogue: 0,0:04:24.91,0:04:30.21,Default,,0000,0000,0000,,but are simply unaware of road \Nconditions ahead— and drive accordingly.