Of all humanity's inventions, one of the least glorious is the traffic jam. Right now there are - who knows how many million people - sitting in cars, staring with grumpy faces at the car in front.
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The problem of traffic is partly engineering and partly psychology. Sitting in the left lane, we notice cars streaming past on the right. The temptation is to hop lanes, only to discover a moment later, the left lane is passing you.
When a gap opens up in your lane, it feels like we should speed up. However, that just puts you on the bumper of the next car, and a moment later you'll have to slow again.
The spaces between vehicles provides a cushion against perturbations in the flow. If one vehicle changes speed, the car behind can close the gap slightly and is less affected. With no gap between vehicles, every minor change ripples downstream, making a traffic jam more likely.
Some years ago, the ABC science unit ran two cars at the same time on identical routes. One driver just ''went with the flow'', while the other was a lead-foot, aggressively chasing the gaps. The net result was a tiny difference in their trip time.
Traffic is a textbook example of a system. It is the combined result of many parts and the resulting behaviour can be hard to predict.
To alleviate congestion, you might well say the government should build more roads.
Maybe. Or maybe not, because sometimes the obvious answer is wrong. It turns out, an additional road can actually make things worse!
German mathematician Dietrich Braess first observed this can apply to roads, giving rise to the phenomenon now called ''Braess' Paradox''. The logic behind this is a little obscure, but it's another example of where systems don't do what we expect.
The Boston ''Big Dig'' was plagued by problems, and ended up costing more than $8 billion, making it the most expensive highway project in US history. New bridges and tunnels rerouted the Interstate 93 through the heart of the city.
Did it work? Not according to a 2008 Boston Globe report, which said ''many motorists ... are spending more time stuck in traffic, not less.''
Partly this was the change in flows through the road network.
It's also an example of Jevons paradox where people are lured to consume more when a product becomes more efficient. Spending this much money on roads encouraged people to drive more often.
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