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Hedge-blog: study on passing distances

2nd December 2013

Ian Walker, famous for cycling wearing a long wig, to look like a woman and see if it had an effect on driver behaviour, has produced a new study. Together with Ian Garrard (who did the cycling this time) and Felicity Jowitt, he tested passing distances on a 26km (each way) commute in Berkshire, using seven different outfits. These outfits were called commute, casual, hiviz, racer, novice, police, and polite.

Specifically, the 'police' outfit said 'POLICEwitness.com - move over - camera cyclist', and the 'polite' outfit said 'POLITE notice - please slow down' on the back. 

The journeys were made between December 2012 and May 2013, and the passing distances were measured with an electronic sensor. 

The average passing distance was 117.50cm. This compares with an average passing distance of 179cm measured in a study by Watts in 1979, suggesting that drivers are giving cyclists a lot less space than 34 years ago. 

On average, drivers passed closest with the 'polite' outfit (114.05cm), and furthest from the 'police' outfit (122.12cm). There was also a difference in drivers passing very close, according to outfit. The percentage of drivers passing within:

  • 100cm was 43% with the 'polite' outfit, and 24.5% with 'police'
  • 75cm, 9.2% 'polite' and 4.1% 'police'
  • 50cm, 2.1% 'polite' and 0.5% 'police'

The researchers observed, subjectively, overt acts of aggression when wearing the 'polite' outfits.

The study paper points out that close-passing motor vehicles can create a subjective experience of being unsafe (even though they don't hit the cyclist) which can be a disincentive to travel by bicycle.

Another interesting pattern to emerge from their data was that where a vehicle is following close behind another vehicle, the second driver leaves less space when passing (2.28cm less on average). This coincides with my own experience.

Other than the differences between the 'polite' and 'police' outfits, motorists did not change their behaviour significantly depending on the perceived level of experience of the cyclist. The 'novice' outfit resulted in very similar passing distances to the 'racer' outfit. The researchers found that riders' outfits could not prevent the closest overtakes. The solutions are infrastructure, education, and legal (strict liability, strong policing of dangerous driving).

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