Convertible Cars Are Actually Safer Than Hardtops, Says Study

Convertible Cars Are Actually Safer Than Hardtops, Says Study

Crash statistics show no additional risk to convertibles

Convertibles may not seem as safe as other vehicles when driving on the highway with the roof down, but accident statistics tell a different story, according to new IIHS research.

Despite the relatively fragile appearance of their roof structures, recent model convertibles are no more risky than non-convertibles, according to the analysis of accident and death rates.

In fact, driver accident and death rates were lower for convertibles than for non-convertible versions of the same cars. However, the differences in driver mortality rates were not statistically significant.

“These results do not suggest that convertibles offer better protection to their occupants than other cars, but they indicate that there is no statistical basis to fear that the absence of a permanent roof makes them more dangerous” said Eric Teoh, director of statistics at the IIHS. services, who wrote the document.

Teoh compared police-reported driver death and accident rates per kilometer traveled for convertible and non-convertible versions of 1- to 5-year-old models in 2014-2018. He also compared the driver’s circumstances and behaviors associated with fatal accidents, examining factors such as the point of impact and whether the driver was ejected from the vehicle, as well as the impairment and use of the seat belt. .

Data on drivers killed in crashes came from the National Highway Traffic Safety Administration (NHTSA) fatality analysis report system. Information on the number of accidents declared by the police came from the General Estimation System of the National Motor Vehicle Sampling System and from the Accident Report Sampling System which replaced it in 2016, also updated. day by NHTSA.

Teoh found that convertibles were involved in 6 percent fewer police-reported collisions per kilometer traveled than their conventional counterparts. Driver mortality rates were 11% lower. However, the likelihood of the driver being ejected from the vehicle in a fatal accident was higher for the convertibles than for the conventional versions.

Previous research has shown that for conventional cars, a stronger roof reduces the risk of serious or fatal injury and the likelihood of ejection in the event of a rollover. The IIHS added a roof strength assessment to its crashworthiness testing program in 2009, making a good rating a requirement for the TOP SAFETY PICK award a year later.

Convertible stretch fabric with a retractable hardtop is exempt from the NHTSA’s current roof crush resistance requirements. However, some manufacturers have voluntarily reinforced the A-pillars on each side of the windshield and installed roll bars to provide additional protection in the event of a tip-over.

When the IIHS evaluated a group of medium-sized convertibles in 2007, most of the 10 models obtained good or acceptable ratings in the front and side impact tests, although eight had poor or marginal head restraints. Since then, convertibles have remained a low priority for the test program due to their low sales volumes.

This year, the IIHS-affiliated Road Loss Data Institute also compared data on insurance claims for vehicles available in convertible and non-convertible versions, finding that convertibles had rates lower injuries and collisions.

Teoh found little difference in most fatality circumstances for convertible and non-convertible vehicles. In both cases, approximately a quarter of the fatalities occurred in rollover crashes, approximately half occurred in single vehicle crashes, approximately 60% were the result of head-on collisions and approximately 20% were the result of side collisions.

However, 21% of cabriolet drivers killed in collisions were ejected from the vehicle, compared to 17% for conventional cars. Among rollover accidents, the probability of ejection was 43% for convertibles against 35% for their non-convertible counterparts.

Cabriolet drivers were slightly more likely to wear seat belts and slightly less likely to speed, although they were slightly more likely to be impaired by alcohol. These differences were too small to suggest a large variation in driver behavior for the two types of vehicles.

Teoh has not been able to account for all of the possible differences in the way convertibles are driven, even when compared to the non-convertible version of the same car. For example, convertible owners may drive them more often in good weather or on less traveled roads, which could affect accident rates.

“Based on this study, the convertibles do not appear to pose a particular safety risk,” said Teoh. “If you are shopping for a convertible, you should consider the crash test ratings and safety features, just as you would if you were buying another car.”

Convertible car accident rate
Teoh, Eric R.
Road Safety Insurance Institute

June 2020

Objective: Convertible cars have been around since the earliest automobiles, and the lack of a substantial roof structure creates safety concerns. While crash tests have shown that convertibles can withstand excessive intrusion into frontal and side collisions and that solid A-pillars and roll bars can help maintain survival space during rollovers, little work was done to examine the actual collision experience of these vehicles. The objective of this study was to compare the collision experience of recent convertibles with non-convertible versions of the same cars using the most recent collision data.
Methods: Driver death and police-reported collision rates were compared for convertibles 1 to 5 years old and their non-convertible versions in 2014-2018. Exposure metrics included years of vehicle registration and miles traveled (VMT). These rates were compared using the standardized mortality rate to account for possible differences in the distribution of exposure. The circumstances of the accident (for example, point of impact, rollover, ejection) and behavioral outcomes (for example, speeding, alcoholism, use of seat belts) were compared for drivers killed in crashes .
Results: Convertibles had lower police-reported driver death and collision rates, based on years of vehicle and VMT registrations. However, the differences in driver mortality rates were not statistically significant. Driver deaths for 10 billion VMT were 11% lower for convertibles, and driver involvement in police-reported accidents for 10 million VMT was 6% lower. On average, convertibles traveled 1,595 miles less per year than the non-convertible versions of these cars. Among fatally injured drivers, convertibles had higher ejection rates and differences in behavior were minimal.
Conclusions: The safety concerns associated with the lack of a substantial roof structure for convertibles have not been confirmed by the results of this study. Minimal differences in behavioral results suggest that the study design minimized the differences in the study groups.
Practical applications: convertibles do not pose a risk to consumer safety. Consumers interested in convertibles should consider the crash test ratings, safety features and size and weight of the vehicle, just as they would if they purchased a non-convertible car.

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