SourceFlickr: The Commons. Photographer: gi-ei. Title: Menacing bike.

Germany has some of the most stringent and advanced bicycle lighting regulations in the world. And it is in Germany that bicycles are prohibited from having flashing lights for the reason that they have historically been reserved for emergency vehicles under the national traffic code (the StVZO). In support of this regulatory standard, some argue that having a steady (i.e. non-blinking) rear light at night allows motorists to better judge their distance from cyclists thus enabling motorists to more confidently and thus safely pass them. At least one bicycle helmet safety study,* however, indirectly suggest that a steady light may not in fact enhance safety in the manner suggested. This study and our own (admittedly anecdotal) experience suggest that motorists do provide less space to helmeted cyclists when passing in comparison to un-helmeted cyclists. They regularly speculate that such behavior results from motorists presuming that helmeted riders are more experienced and thus less likely to maneuver unpredictably and (more disturbingly) better protected and thus requiring less diligence when passing. The intuition and experience of IDC staff is that a steady rear light "may" have a psychological effect on motorists similar to that of helmeted cyclists. Common sense suggests that increased certainty of distance between motorist and cyclist is likely to promote higher confidence in passing - at higher speeds and with narrower gaps.

The question of flashing lights is of course not black and white, IDC staff believes that context is also an essential consideration. Flashing lights have an advantage of increasing the conspicuity of cyclists in urban areas which normally have high levels of light pollution from multiple and varied sources. Think of automobiles (with 6000 lumen xenon headlights), street lighting and distractions such as brightly lit store fonts. For city riding where street lights are often adequate for navigation and light “noise” may be high, it makes sense that blinking front and rear lights could greatly enhance cyclists’ conspicuity. This is likely to be particularly so in jurisdictions where blinking lights are already a norm for bicyclists and drivers are accustomed to associating blinking lights with their slower pace and often more erratic movements (with implications for passing distance). This analysis likely also applies in rural areas where blinking lights are already associated with cyclists and bicycle traffic shares the road with high-speed motorised traffic. Of course, this applies only in jurisdictions where it is legal for bicycles to have flashing lights.
Nevertheless, in rural conditions with lower speed traffic, fewer sources of light pollution and particularly during group rides at night, it also makes sense that a steady light might be social courtesy if not simply appropriate.

*            Ian Walker (2006), “Wearing a helmet puts cyclists at risk, suggests research“, University of Bath Press Release, accessed 29 January 2013.


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