Motorcycle crash injuries became more serious after Michigan repealed its mandatory helmet law in 2012.
The Insurance Institute for Highway Safety teamed up with researchers at the University of Michigan Injury Center, the University of Michigan School of Medicine, and the University of Michigan Transportation Research Institute to look at the numbers.
They found that skull fractures after a motorcycle crash increased nearly 40% in the year after the state Legislature said riders over age 21 could skip wearing a helmet if they so chose.
Russ Rader of IIHS says skull fractures are more likely to require intensive care and neurosurgery. He thinks it's shortsighted to say not wearing a helmet is about personal freedom.
"It affects all of us ultimately," says Rader, "not only in terms of health care costs, but what we pay for insurance."
Many other states also repealed their helmet laws in the past decade. Only 19 states and the District of Columbia still have them.
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