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Hazardous Journey

Car colour and risk of car crash injury: population based case control study

BMJ 2003; 327 doi: (Published 18 December 2003) Cite this as: BMJ 2003;327:1455

Author's response

Thankyou for the interest in and responses to our study of the
association between car colour and car crash injury. The following
addresses some of the recurring points raised in correspondence on this
website and in direct e-mail.

We would expect that car colour is more important in conditions of high
illumination ie daylight, because cone receptors in the eye which are
responsible for colour vision, are more active in high illumination
situations. In low illumination situations the rod receptors in the eye
predominate and vision is more black and white. We would expect that the
lightness or darkness of the colour (ie how it would appear in a black and
white photocopy) would be more important than the actual hue.
Reflectivity of the colour may be important too, given there is usually
some light source eg headlights or streetlights.

We attempted to compare the effect of silver car colour in daytime
and night time. We were unable to show a difference in the odds ratios for
silver cars in daytime (adj OR 0.45, 95% CI 0.18 to 1.15) compared to
night time (adj OR 0.69, 95% CI 0.17 to 2.90) - the confidence intervals
are wide and overlapping.

The multivariable analysis is adjusted for confounding due to weather
– fine versus wet or foggy.

This study was the first of its type to look at the association between
car colour and car crash injury. As we state in the conclusion it is
uncertain to what extent our findings are generalisable to other settings.
For example, there is no snow in Auckland in winter, and snow may
influence the visibility of silver cars, which may make a difference to
the “safety”.

We took the view, in accordance with many injury researchers, that the
responsibility for a crash is seldom solely attributable to one driver.
The cars included in this study are all those in which occupant(s) were
injured or killed irrespective of whether they were responsible for the
crash or the ‘victim.

We had no data on the value of the cars. In the regression model we did
test the age of the car (since first registration) and engine size (less
than 2000cc or 2000cc and greater) as a proxy for size of the car.
Neither of these factors were associated with significant confounding.

The perception that silver cars were expensive, late-model prestige
cars with advanced safety features, was not true of our study. Silver
cars in Auckland at the time of the study (1998-9) made up 11% of the cars
and makes (in alphabetical order) were honda, holden, mazda, mitsubishi,
nissan, and toyota, with a variety of models.

We speculate that perhaps silver cars are “safer” because they are more
visible in our setting, being both light-coloured and reflective. If all
the cars were silver would the “benefit” diminish due to reduced
conspicuity of a particular silver car? We don’t know.

Competing interests:
Author of the published report

Competing interests: No competing interests

19 January 2004
Sue Furness
Research Fellow
Auckland NZ