BBC Future

In Depth

The road design tricks that make us drive safer

(SID)

(SID)

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

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%.

(Traffic Safety Foundation Vancouver)

In Vancouver, trompe l’oeil paintings aim to make drivers slow down at high-risk intersections (Traffic Safety Foundation Vancouver)

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.

(Final Mile)

Diagonal speed breakers create an unfamilar feeling when driving over them, and this makes drivers reduce their speed (Final Mile)

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. “This is where we open the door into a universe of nudging by influencing perceptions,” adds Hansen.

(AFP/Getty Images)

Life-size cut outs of traffic policemen are used in Bangalore to dissuade motorists from committing traffic violations. (AFP/Getty Images)

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.

Towing the line

But not all nudging needs to be that elaborate or even lifelike. Painting jagged or sharp lines on the road can frighten drivers enough to slow down, says Prasad. The lines appear haphazard, and the unfamiliarity forces drivers to slow down.

Chicago’s Department of Transportation had success with another simple illusion on a notorious hot-spot for crashes, a bend at Oak Street on Lake Shore Drive. City officials tried nearly everything: making lane markings clearer, putting up bigger warning signs, flashing lights at the side of the road. All in vain; drivers just kept crashing.

In the end the department painted white lines across the road – each line closer to the next as cars got nearer the curve. This perception of shrinking distances makes drivers think that they’re going faster than they really are. According to a study there were 36% fewer crashes in the six months after the lines were painted in September 2006 compared to the same six-month period the year before. Hansen believes this is one of the best psychological tricks to reduce speeding.

Novelty effect

Such measures tend to work better than road signs because, like most visual information, they speak to our brain at a subconscious level. “When we see a sign, if we see a sign at all – for we may have trained our brains to typically ignore them – we may question its applicability to us, or its general validity,” says Tom Vanderbilt, the author of Traffic, a book that explores how “perceptual countermeasures” can improve safety on the road. “But driving down a quite narrow street, or over a series of whizzing bars, you are less likely to think about it and more likely to just reflexively slow down,” he says.  

And this works much better than visual illusions, he adds – because the danger is once you know something is fake, you may quickly start to ignore it. “As with all experimental treatments, there is the question of a novelty effect, of drivers eventually returning to their old behaviour once they've 'figured out' the trick,” says Vanderbilt.

Seven years ago in India, one inventive maker of car suspensions placed 3D stickers on the road that looked like fake potholes. The plan was to persuade drivers to buy this company’s suspension systems, suggesting that drivers would enjoy a smooth ride even on rough roads. Instead the stickers persuaded speeding drivers to slow down.

Similarly, in Philadelphia, Pennsylvania, road planners painted 3D illusions of speed bumps. But, as Hansen points out, “a widespread introduction of fake speed bumps may ultimately lead to hazardous driving behaviour even at real speed bumps".

So how far can road-safety nudging go? Hansen thinks a lot more. For one, the dividing line could be removed, because “it works as a subtle cue to speed up, as it marks one’s ‘safe territory’,” he says. And why focus only on the roads? Steering wheels could come with two red handprints, only visible when the driver’s hands are not on the wheel, to get people to drive with both hands. “We psychologically prefer things to be in their right place – and the same might work for steering wheels.”

If you would like to comment on this, or anything else you have seen on Future, head over to our Facebook or Google+ page, or message us on Twitter.