What you need to know about shockwave traffic jams

In this post-COVID era, more of us are expected to ditch public transport in favour of driving ourselves to work. With more Australians on the roads means more traffic and the inevitable shockwave traffic jam effect.

Sometimes there’s an accident or other obvious reason for the jam that’s hard to stay frustrated at. But have you ever been trapped in slow-moving traffic for no apparent reason and then flown out the other end with miraculous open road ahead of you? If so, you’ve encountered a shockwave jam (or a ‘traffic wave’, as they’re sometimes known).

You ready to be even more infuriated? That jam may have been caused by one single tap on the brakes. Detailed explanations belong to the realm of equations and fluid dynamics, but it’s a simple thing to understand simply.

Say a car brakes on a freeway and there isn’t sufficient distance for the car behind it to continue at the same speed. This means the car behind it has to brake in turn. However, because human reactions aren’t instantaneous, the car behind has to slow a little bit more than the car in front of it to avoid a collision.

This effect cascades from car to car and, eventually, you’re sitting at a standstill, wondering if dinner’s getting cold.

Here’s the effect in action:

So what can be done? Interventions like stop-and-go freeway entrances and variable speed limits help, but you can do your part as well. Because these kinds of jams are caused by insufficient distance between two cars, it’s best to keep your distance. As tempting as it is to accelerate into new space a lane over, you’re best keeping your cool and keeping the same amount of distance between the car in front of you and the car behind.

Though it might not seem like you’re getting there faster, in the long run, you are. Of course, none of these problems would occur with self-driving cars, but that’s a story for another day...

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