Why the @#$% is there so much traffic? - Benjamin Seibold

翻译人员: Lipeng Chen 校对人员: Joyce He

You’re cruising down the highway when all of a sudden

你正在高速公路上开着车，突然间，

endless rows of brake lights appear ahead.

前方出现了无数排刹车灯。

There’s no accident, no stoplight,

没有事故，也没有红灯，

no change in speed limit or narrowing of the road.

限速没有变化，路也没有变窄。

So why the @#$%! is there so much traffic?

那么，为什么路突然变得这么堵？

When traffic comes to a near standstill for no apparent reason,

当交通没有缘由的停滞时，

it’s called a phantom traffic jam.

这种现象被称为“幽灵堵车”。

A phantom traffic jam is an emergent phenomenon

幽灵堵车是一种突发现象，

whose behavior takes on a life of its own, greater than the sum of its parts.

很难加以控制， 且整体状况比各部分之和还糟糕。

But in spite of this, we can actually model these jams,

但尽管如此，我们事实上可以 对这类拥堵建立模型，

even understand the principles that shape them—

甚至理解它们形成的原理——

and we’re closer than you might think

想要在将来避免此类交通拥堵，

to preventing this kind of traffic in the future.

事实上，我们其实已经比你 想象的还要更进一步了。

For a phantom traffic jam to form, there must be a lot of cars on the road.

幽灵拥堵的形成需要 路上有很多辆车。

That doesn’t mean there are necessarily too many cars

这不一定意味着车太多了

to pass through a stretch of roadway smoothly,

以至于无法顺利通过某一路段，

at least not if every driver maintains the same consistent speed and spacing

至少当每个司机都与其他司机保持 一致的速度和间距时，

from other drivers.

幽灵堵车就不会发生。

In this dense, but flowing, traffic,

在这密集但流动着的车流中，

it only takes a minor disturbance to set off the chain of events

只要有细微的变动 就会造成连锁反应，

that causes a traffic jam.

导致堵车。

Say one driver brakes slightly.

比如一个司机稍稍踩了刹车。

Each successive driver then brakes a little more strongly,

后面的每一个司机就会 踩刹车踩得更重，

creating a wave of brake lights that propagates backward

致使路上的车辆形成

through the cars on the road.

一条向后延伸的刹车灯浪。

These stop-and-go waves can travel along a highway for miles.

这种停停走走的情况 可以在高速公路上绵延数英里。

With a low density of cars on the road,

当路上车流密度较低时，

traffic flows smoothly because small disturbances,

交通会很顺畅，因为小的干扰，

like individual cars changing lanes or slowing down at a curve,

比如个别车辆变道或弯道减速，

are absorbed by other drivers’ adjustments.

可以被其他司机的调整所抵消。

But once the number of cars on the road exceeds a critical density,

但是一旦路上车辆的数量 超过临界密度时——

generally when cars are spaced less than 35 meters apart,

一般来说指车距小于 35 米——

the system’s behavior changes dramatically.

整个系统的行为 就会发生巨大变化。

It begins to display dynamic instability, meaning small disturbances are amplified.

首先会出现动态不稳定性， 也就是说小的干扰会被放大。

Dynamic instability isn’t unique to phantom traffic jams—

动态不稳定性并不是 幽灵堵车所特有的——

it’s also responsible for raindrops, sand dunes, cloud patterns, and more.

它也存在于雨滴、沙丘、 云朵形态等等。

The instability is a positive feedback loop.

这种不稳定性是种正反馈回路。

Above the critical density,

在临界密度之上时，

any additional vehicle reduces the number of cars per second

任何额外的车辆都会降低 每秒通过路上某一点

passing through a given point on the road.

汽车的数量。

This in turn means it takes longer for a local pileup

这反过来意味着需要更长的时间 才能让局部的一队车辆

to move out of a section of the road, increasing vehicle density even more,

通过某段道路， 更进一步增加了车流密度，

which eventually adds up to stop-and-go traffic.

最终导致了停停走走的交通。

Drivers tend not to realize they need to break far in advance of a traffic jam,

司机往往意识不到他们要 远在堵车之前就刹车，

which means they end up having to brake harder to avoid a collision.

这意味着他们最后要狠狠的刹车 来避免撞车。

This strengthens the wave of braking from vehicle to vehicle.

这加强了车与车之间刹车的传递。

What’s more, drivers tend to accelerate too rapidly out of a slowdown,

更糟糕的是，司机在减速后 往往会加速过快，

meaning they try to drive faster

也就是说他们会比

than the average flow of traffic downstream of them.

后方的平均车流开得更快。

Then, they have to brake again, eventually producing another feedback loop

然后，他们必须再次刹车， 最终形成另一个反馈回路，

that causes more stop-and-go traffic.

造成更多停停走走的拥堵。

In both cases, drivers make traffic worse

在这两种情况中，司机让 堵车变得更糟糕了

simply because they don’t have a good sense of the conditions ahead of them.

仅仅因为他们不能很好地 预知前方的车况。

Self driving cars equipped with data on traffic conditions ahead

自动驾驶汽车配有前方路况的数据，

from connected vehicles or roadway sensors

这些数据来自于 互联的车辆或路况传感器，

might be able to counteract phantom traffic in real-time.

可能可以实时避免幽灵堵车。

These vehicles would maintain a uniform speed, safety permitting,

在保证安全的情况下 这些车辆会保持一致的速度，

that matches the average speed of the overall flow,

和整体车流的平均速度匹配，

preventing traffic waves from forming.

进而避免拥堵车潮的形成。

In situations where there’s already a traffic wave,

在已经存在拥堵车潮的情况下，

the automated vehicle would be able to anticipate it,

自动驾驶汽车可以进行预测，

braking sooner and more gradually than a human driver

相比人类司机更早 并且更缓慢地刹车，

and reducing the strength of the wave.

从而降低拥堵车潮的强度。

And it wouldn’t take that many self-driving cars—

这并不需要很多辆 自动驾驶汽车就能实现——

In a recent experiment, one autonomous vehicle for every 20 human drivers

在最近的一次实验中，每 20 名人类司机 对应一辆自动驾驶汽车，

was enough to dampen and prevent traffic waves.

就足以缓解并预防拥堵车潮形成。

Traffic jams are not only a daily annoyance–

堵车不仅仅是日常的烦恼，

they’re a major cause of fatalities,

还是意外死亡、资源浪费

wasted resources, and planet-threatening pollution.

和地球污染的主要原因。

But new technology may help reduce these patterns,

但是新型技术 可以帮助减缓这些状况，

rendering our roads safer,

让我们的道路更加安全、

our daily commutes more efficient, and our air cleaner.

日常通勤更加有效、 空气更加清洁。

And the next time you’re stuck in traffic,

下次你再遇到堵车时，

it may help to remember that other drivers aren’t necessarily driving spitefully,

这样想想也许会有帮助： 其他司机并不一定是存心这样的，

but are simply unaware of road conditions ahead— and drive accordingly.

他们只是无法预测前方的路况， 并相应地调整驾驶策略。