SourceFlickr: The Commons. Author: French, J.A., Keen.

Should cyclists consider turning lights on during the day now that an increasing number of jurisdictions are requiring Daytime Running Lamps (DRLs) for automobiles and motorbikes? We think yes and particularly so if you are a small or at least slim cyclist. The reason is that persuasive evidence suggests the most important factor in bicycling accidents is the physical size of the cyclist. It may come as no surprise that small cyclists are more at risk for bicycling accidents. However, for both obvious and unintuitive reasons, physically smaller cyclists also seem to be more risk from bicycling accidents. These were key findings in one of the broadest and well documented research projects on bicycle accidents conducted in New Zealand, which found that the extent to which a cyclist is overweight* incrementally reduced the likelihood of that cyclist being involved in an accident over time.** Less intuitively, the study also found that, in the event of an accident, the degree to which a cyclist was overweight also incrementally reduced likelihood of severe injury. Remarkably, overweight cyclists are: less likely to be involved in bicycling accidents; suffer severe injury from them; and apparently  the bigger the better.

Of course being large increases conspicuity with obvious implications both for the ability of motor vehicles operators to detect bicyclists, as well as the distances at which they are detected (longer being better), thus allowing them to be avoided. Intuitively, the relative inconspicuity or visibility of smaller cyclists seems at least a partial explanation of their relative susceptibility to accidents. Less intuitively (or at least somewhat troublingly), the researchers also discussed the hypothesis that drivers in large metal vehicles were simply less concerned about smaller obstacles (i.e. bicyclists) that would cause less damage in the event of collision.
By way of disclaimer, we note here that we are not in any way advocating laxity by larger bicyclists in taking precautionary measures whether in terms of riding defensively or increasing conspicuity. Similarly, the finding suggesting that overweight cyclists are more likely to be seen and less likely to be severely injured in bicycling accidents should certainly not be seen as a green light to put on the pounds: obesity is itself a health risk. Notably, all but the very largest of bicyclists remain smaller and less conspicuous than motorcycles, which are themselves widely known to be at risk due to their relative inconspicuity, particularly vis-à-vis automobiles.
IDC staff considers it likely that bright lights on bicycles during the day would have prevented at least some if not a statistically significant number of the accidents involving smaller or at least slimmer cyclists. This would be even more so the case for all bicyclists under low light conditions (such as dawn and dusk) or reduced visibility conditions (such as in rainy or foggy weather). Moreover, the results of this study also indirectly underscores the critical importance of conspicuity for young riders (not specifically addressed as a category of rider in this study),*** who are not only less visible to drivers (on average), but also less likely to be experienced with practicing defensive riding techniques. In this respect, we consider any enhancement to conspicuity, including during the day, via having bicycle lights on during daytime or DRLs, which hub dynamo headlamps are increasingly being equipped with for instance, is an idea meriting solemn consideration.

And should you have any doubt, let's do a little mental exercise. What if ...

*            Based on the well know Body Mass Indicator (BMI) indicator.
**          S J Thornley, A Woodward, J D Langley, S N Ameratunga and A Rodgers (2008), “Conspicuity and bicycle crashes: preliminary findings of the Taupo Bicycle Study”, Injury Prevention, 4;11-18.
*** (????), “How many children die each year from bicycle accidents?”, accessed 23 January 2013.


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