A new report says the improving economy has a downside: more traffic deaths. The Insurance Institute for Highway Safety (IIHS) says a stronger economy fuels more driving, leading to an increase in deadly crashes.

The IIHS researchers analyzed fatal crash data collected by the federal government between 2012 and 2015. They found overall, smaller vehicles on the road don’t protect occupants the way that larger ones do, reports CBS News correspondent Anna Werner.

Mini and small cars topped the IIHS list of vehicles with the highest number of driver deaths. The Hyundai Accent sedan and the Kia Rio sedan, both mini cars, had the highest rate of deaths.
In a statement, Hyundai said safety is their “number one priority” and they “are very confident that the Accent performs safely.” CBS News reached out to Kia but did not immediately hear back.
“We’ve always seen higher death rates in smaller cars. It’s consistent,” said Chuck Farmer, the lead researcher on the study. “I don’t see any benefit from a safety standpoint to having a smaller car.”

Only two large vehicles, the Dodge Challenger and the Nissan Titan Crew Cab, made the top 10 for highest rates of driver deaths. Dodge did not respond to a request for comment. Nissan said in a statement it is “committed to the safety and security of our customers and their passengers” and will “evaluate the data in this report to identify improvement opportunities.”

For the study, the IIHS looked at 2014 model cars and earlier equivalent models. Of the models with the lowest rates of driver deaths per year, more than half were mid-size or larger. Eleven vehicles, including the Mazda CX-9 and the Jeep Cherokee, had zero driver deaths between 2012 and 2015.

Overall, the IIHS found cars are performing better in crash tests and vehicle safety technology continues to improve. But IIHS researchers say there’s a limit to what improved vehicle designs and safety technology can prevent from happening.