A theory known as “risk compensation” holds that when additional safety measures are implemented,” individuals feel safer to take greater risks, effectively keeping their overall risk the same.
A study conducted in France suggested that could be true, at least for men. Researchers gave men and women cycling helmets and then measured how fast they were going. Women rode about 10.3 mph while wearing helmets and 10 mph without helmets. Men, on the other hand, rode 10.4 mph without helmets, but cranked it up to nearly 12 mph with helmets.
Nonetheless, the researchers determined the increase in speed was not likely to offset the significant health benefit of wearing a helmet.
— Markian Hawryluk, The Bulletin