Colour me safer

In 1907 the Chicago Yellow Cab Company chose the colour of its cars based on a survey conducted at a nearby university. The survey showed that yellow was the most noticeable colour and led the company to infer that this would make it easier for potential passengers to spot their taxis in the sea of mass produced black cars prevalent at the time. Now, more than a century later, it turns out that yellow was a wise choice for a new study is revealing that taxis of that colour are much less likely to get into accidents than taxis of other colours.

The new work made use of a merger that took place between two taxi companies in Singapore during 2002. One of the companies used yellow cars and the other one used blue cars. Today, the company owns 4,175 yellow taxis and 12,525 blue ones. 

The researchers analysed 36 months of detailed taxi, driver, and accident data that the taxi company supplied to them and found that there is an unquestionable link between colour and accidents. In total, yellow taxis had 6.1 fewer accidents per 1,000 taxis per month than blue taxis. That suggested that colour alone granted a 9% reduction in accident probability. The researchers found this hard to swallow so they set off to explore whether the driver populations had any significant differences. To do this, they analysed the demography and driving behavior of a random sample of 3,341 drivers for 3 months using 15 second interval location and status data from the taxis. This amounted to more than 150 million data points and showed that the drivers were driving nearly identically. Mechanical differences were also ruled out since the taxi company uses a single car model and all cars undergo the same service schedules.

This led the team to question whether yellow taxis were protected by simply being more noticeable than blue taxis. To test this idea, the researchers delved into detailed accident reports and looked for the nature of the accident and the lighting conditions in which it occurred. They theorised that if yellow had a protective effect, a yellow taxi would be less likely than a blue taxi to be involved in an accident when the taxi was clearly in the other driver’s view. This proved true. They also theorised that yellow would grant an even greater advantage at night since yellow has a stronger contrast than blue against a dark background. You can read more in The Economist article that I wrote on this here.