There’s perhaps no more frustrating human experience than sitting in traffic on a busy road. It’s one thing when there’s been an accident or construction has diverted the flow of vehicles. But sometimes, for no perceptible reason, we’re all just…sitting there.

When traffic backups occur without any obvious cause, they’re sometimes called “phantom” traffic jams. Believe it or not, scientists and engineers have been studying the phenomenon for years in an effort to design better infrastructure.

A 2008 study finally revealed the cause of phantom traffic jams

Yuki Sugiyama, a physicist at Nagoya University, and his colleagues wanted to understand why traffic slows or comes to a stop even when there’s no bottleneck.

So they decided to create the perfect driving conditions—ones in which a traffic jam couldn’t possibly form. They had 22 cars drive in a loop on a closed track. The participants were instructed to maintain a constant speed of 30 km/h, and the track provided plenty of room for........

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