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When conventional road signs have no effect, designers are turning to increasingly clever ways to subconsciously make drivers slow down or pay attention.

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A spooky, black human silhouette suddenly appeared out of nowhere on the roadside of a picturesque country road in southern France. It was the size of an adult, but it had no face; instead, a lightning bolt seemed to split its head in two.

Speeding down this road with no traffic, no lampposts and no speed traps – just ancient plane trees towering on both sides – I dismissed the figure as a weird prank. But then there was another. And then two more, an adult and what looked like a child. Then it dawned on me. The cut-outs represented people who died on this road in car accidents. The message came across: I slowed down.

It’s a not-too-subtle example of a strategy known as behavioural science or nudging – techniques that make people act or respond in a certain manner. Some nudging tactics are straightforward or obvious. Signs displaying speed, speed limits or reminding drivers to take regular breaks try to capture the driver’s attention directly. Others are more subtle; like the “average speed” cameras. While normal speed traps try to catch speeding drivers at one single spot, average speed cameras punish drivers who cover the distance between point A and B too fast. The nudging works: when in 2005 average speed cameras were installed on a 32-mile stretch of the A77 motorway near Glasgow in Scotland, the amount of road casualties fell 37%.

Then there are measures that tap more into the subconscious. Some road construction sites use smiley signs to influence driver behaviour: At the start of the road works the smiley is sad – but it gets progressively happier as you’re nearing the end of the construction zone. The goal is to keep drivers alert and decrease their frustration while they have to keep to a lower speed limit. In a similar vein speed boards in the UK have had a smiley added underneath. They smile at cars under the speed limit, and frown at those that go above it.

Bumping behaviour

Roads in some countries are clearly more dangerous than in others. India accounts for 10% of all road fatalities – about 137,000 people died on Indian roads in 2011 alone. Even though the country’s first access-control motorway – the six-lane Mumbai-Pune Expressway is relatively less dangerous than cramped urban streets, there have been more than 2,000 accidents, with at least 500 fatalities, in its 12 years of operation. Nudging is one way of dealing with the problem. Final Mile is a Mumbai-based behavioural science and design firm that hopes it can play mind tricks with Indian drivers to persuade them to slow down and pay more attention.

More than three-quarters of accidents happen because of a human error, says Ram Prasad, one of the company's co-founders. Specifically, five aspects of human nature are at play: overconfidence; inattention; skewed perception of risk; lack of feedback; and lack of empathy – due to poor eye contact at high speeds.

So, to get overconfident and inattentive drivers to slow down at India’s more than 13,000 open railway crossings, Final Mile has installed speed-bumps that run diagonally, rather than perpendicular, to the road. The front wheels of a car cross the bump one after the other, rather than in unison, making the car swing from side to side. “They bring in unfamiliarity,” says Prasad, “motorists tend to slow down significantly and therefore pay more attention to an oncoming train.” On the Mumbai-Pune Expressway, these speed-breakers are also painted with thicker yellow lines, making them appear higher. This tricks the drivers, forcing them to reduce speed before approaching them.

Going the extra smile

Another tactic is to humanise signage. The black silhouettes on French and Canadian roads are one example, large posters in India showing shocking pictures of a man’s face in a crash are another. “This builds empathy,” says Prasad. “And instead of just saying ‘drive slowly', we show what happens if you drive fast,” he says.

On some UK roads the familiar “Children crossing” sign with outlines of running children has been replaced by black life-size silhouettes of children instead. It works even better if “the children featuring on the poster are saying ‘I live here,’ or ‘I want my daddy to come home safely',” says Pelle Guldborg Hansen, behavioural scientist at the University of Southern Denmark, and chairman of the Danish Nudging Network.

This makes the impact of aggressive driving very obvious, and creates awareness in an automatic, effortless way – which is crucial, says Ivo Vlaev, an experimental psychologist at Imperial College London in the UK.

It falls in-between the extremes of calling attention to your speed and a perception of a possible risk.

Another nudge by illusion is a reminder of the force of the law by using fake police officers. In Bangalore, life-size khaki-clad cardboard cut-outs of policemen are used to persuade drivers to behave. Similar tricks are used in China, the United States and some European countries. In Preston, a town in the UK, motorists hit the brakes after mistaking life-sized metal replicas for real police officers. Some towns have placed life-size cardboard cut-outs of police cars on bridges crossing highways.