Tunnel renaissance: Why cities are hiding roads down in the ground

In JG Ballard's biting satire Concrete Island, architect Robert Maitland ploughs his Jaguar off the M4 and wakes up trapped within a tangle of slip roads. The novel was published in 1973, when motorways were all the rage. But that dystopian vision of chunky flyovers and tangled roads in the sky is disappearing, as cities around the world are electing to hide roads down in the ground.

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