It’s an odd look, the one people shoot you when you tell them you’ll be spending the afternoon driving over illusory speedbumps.



Well, fake speedbumps may not be real, but that doesn’t mean they don’t work. TfL trialled them in Newham, London in 2014, cutting traffic speeds there by 3mph. They are painted humps on the road: white arcs, about a metre wide, like slightly asymmetrical Vs that, by the miracle of perspective, fool the eye into seeing them as looming out of the tarmac as drivers approach.

Now London’s transport authorities are rolling out a broader trial, centred around Southwark. The precise locations of the fake speedbumps have been kept secret, hinting at the tricksy psychology that underpins them.

Painted ‘speedbumps’ in Southwark, London. Photograph: Martin Godwin/The Guardian

The city is under pressure from multiple directions. The new paint-bumps are part of its attempt to square the circle between Vision Zero – the long-term goal of targeting zero traffic deaths in London – and Sadiq Khan’s big push for cleaner air. TfL controls only 5% of the city’s roads, but it’s a crucial 5%, carrying 30% of all London traffic. (The various London boroughs are independently trialling their own versions.)

Cars emit twice as much CO2 going over traditional traffic bumps as going over traffic “cushions”, those asphalt buttons that have become just as commonplace.



With illusory speedbumps, however, there is no maximum braking – a point at which the car then requires a converse squirt of post-bump acceleration to get going again, and at which the CO2 maxes out.

Instead, as you drive towards them, you simply get a strange, unnerving sense that something weird is happening, somewhere in the road. The illusion isn’t, “Oh that’s a speed bump” so much as, “Oh what’s that”, an unsettling open-endedness that pings your vigilance centres, peaks about 15 metres before you get to the bump, then dissolves like morning mists.

This trompe-l’oeuil painting of a pedestrian crossing in Luoyuan village, Pujiang, China, was devised to attract tourists. Photograph: Feature China/Barcroft Media

My travelling companion was bitterly disappointed. “What even was that?” She’d visualised some cunning piece of urban engineering, rather than a cheap tarmac Banksy. And observing the steady stream of taxis and transit vans that now comprise most traffic in central London, it didn’t feel as if anyone was paying the new urban crop circles much heed.



There’s also a question mark over how effective something like this could be when Southwark’s streets are already a fiesta of no-left-turn signs, bus lanes, C-Charge Zone markers, cycle strips and that other great traffic pacifier: pedestrians who look like they might be about to make a dash for it. The fake speedbumps just add to that cacophony.

The fact that TfL won’t reveal the locations (bar a set of them in Southwark Street that have become widely known) suggests the debate isn’t settled. Does knowing that some speedbumps are 3D illusions destroy their impact? Or could it actually enhance the effect – like the old folk tales of the medicine man who could induce a heart attack just by “cursing” you?

And what about sheer humdrum habit? Does your average taxi driver already have his or her internal speedometer adjusted against the new PSYOPS weapons?

Trompe-l’oeuil 3D painting of a child on a road in Canada

Moving the bumps around to switch-up expectations seems to be part of the plan, like the portable holes in Who Framed Roger Rabbit? “The beauty of these is that rather than men digging in with pickaxes, they only need a quick pressure wash to be moved on,” says Danny Keillor of TfL’s press department.



Besides, similar ideas seem to have produced results elsewhere. Chinese cities have trialled trompe-l’oeuil 3D zebra crossings. India recently began digging up its physical traffic bumps, after concluding that they cause more deaths than they prevent. The most brilliantly macabre version came in Canada, where a school in West Vancouver trialled a mirage of a young girl chasing a pink ball, painted on to the road. Would that even slow jaded Londoners down? Or would a scattering of fake £20 notes be more to our tastes? There’s one trial we’d all like to see.

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