The effect of stricter licensing on road traffic injury events involving 15 to 17-year-old moped drivers in Sweden: A time series intervention study

• Moped crashes are the leading cause of traffic injuries among Swedish adolescents.
• The effect of stricter licensing for mopeds in Sweden was evaluated.
• The intervention was associated with a reduction in moped-related injuries.
• Uncertainties remain regarding the causal mechanisms of the reduction.

IntroductionThis study aimed to evaluate and quantify the effect of the introduction of the AM driving license on non-fatal moped-related injuries in Sweden. With the introduction of the new license category in October 2009, prospective moped drivers are now required to pass a mandatory theory test following a practical and theoretical course. In addition, obtaining a license to operate a moped is now considerably more costly.MethodsTime series intervention analysis on monthly aggregated injury data (1st Jan 2007–31st Dec 2013) was performed using generalized additive models for location, shape and scale (GAMLSS) to quantify the effect size on injury events involving teenage (15–17 years) moped drivers, while controlling for trend and seasonality. Exposure was adjusted for by using the number of registered mopeds in traffic as a proxy.ResultsThe introduction of AM license was associated with a 41% reduction in the rate of injury events involving 15-year-old moped drivers (IRR 0.59 [95% CI: 0.48–0.72]), and a 39% and 36% decrease in those involving 16-year-old (IRR 0.61 [95% CI: 0.48–0.79]) and 17-year-old drivers (IRR 0.64 [95% CI: 0.46–0.90]), respectively. The effect in the 15-year-old stratum was decreased roughly by half after adjusting for exposure, but remained significant, and the corresponding estimates in the other age groups did not change noticeably.ConclusionsThis study provides quasi-experimental evidence of an effect on non-fatal moped-related injuries as a result of stricter licensing rules. Only part of the effect could be explained by a reduction in the number of mopeds in traffic, indicating that other mechanisms must be studied to fully understand the cause of the reduction in injuries.