Crash rates of convertible cars

Teoh, Eric R.
Insurance Institute for Highway Safety
June 2020

Objective: Convertible cars have existed since among the first automobiles, and the lack of substantial roof structure creates some safety concerns. While crash tests have demonstrated that convertibles can resist excessive intrusion in front and side crashes and that strong A-pillars and roll bars can help maintain survival space in rollovers, little work has been done examining the real-world crash experience of these vehicles. The objective of this study was to compare the crash experience of recent convertibles with nonconvertible versions of the same cars using the most recent crash data.
Methods: Rates of driver deaths and police-reported crash involvements were compared for 1- to 5-year-old convertible cars and their nonconvertible versions during 2014–2018. Exposure measures included registered vehicle years and vehicle miles traveled (VMT). These rates were compared using the standardized mortality ratio to account for possible differences in exposure distribution. Crash circumstances (e.g., point of impact, rollover, ejection) and behavioral outcomes (e.g., speeding, alcohol impairment, seat belt use) were compared for drivers killed in crashes.
Results: Convertibles had lower driver death rates and police-reported crash involvement rates on the basis of both registered vehicle years and VMT. However, the differences in driver death rates were not statistically significant. Driver deaths per 10 billion VMT were 11% lower for convertibles, and driver involvements in police-reported crashes per 10 million VMT were 6% lower. On average, convertibles were driven 1,595 fewer miles per year than the nonconvertible versions of these cars. Among fatally injured drivers, convertibles had higher rates of ejection, and behavioral differences were minimal.
Conclusions: Safety concerns associated with convertibles’ lack of substantial roof structure were not supported by the results of this study. Minimal differences in behavioral outcomes suggest that the study design minimized differences in the study groups.
Practical applications: Convertibles do not pose a safety risk to consumers. Consumers interested in convertibles should consider crash test ratings, safety features, and vehicle size and weight, just as they would if shopping for a nonconvertible car.