Use of conspicuity aids by cyclists and risk of crashes involving other road users: population based case-control study

Background: Cycling can improve health and well-being by reducing inactivity. Concern about collision crashes may be a barrier to participation since collision crashes can lead to significant mortality and morbidity. The conspicuity of cyclists may be a contributory factor in some collision crashes. This study investigated whether increased conspicuity aid use (such as reflective or fluorescent clothing) is associated with a reduced risk of collision crashes for cyclists in a UK city.Methods: A matched case-control study was undertaken. Cases were adult cyclists involved in a collision crash causing injury. Controls were adult cyclists matched to cases by time of day, day of week and geographical area of travel. Exposures, potential confounders and route were reported by participants. Odds ratios (OR) and 95% confidence intervals were calculated using conditional logistic regression.Results: 76 cases and 272 controls were included. 69.7% of cases and 65.4% of controls reported using a conspicuity aid on the crash (cases) or index (controls) journey. The unadjusted OR for a collision crash when using any conspicuity aid vs none was 1.2 (95% CI 0.7 to 2.2) and 2.4 (95% CI 1.1 to 5.6) after adjustment for age, gender, index of multiple deprivation score, route risk score and previous bicycle crash.Conclusion: This study found no evidence that cyclists using conspicuity aids were at reduced risk of a collision crash compared to non-users after adjustment for confounding, but there was some evidence of an increase in risk. Bias and residual confounding from differing route selection and cycling behaviours in users of conspicuity aids are possible explanations for these findings. Conspicuity aids may not be effective in reducing collision crash risk for cyclists in highly-motorised environments when used in the absence of other bicycle crash prevention measures such as increased segregation or lower motor vehicle speeds