Roller coasters are fun! Nevertheless, a study in the January 2002 issue of the Annals of Emergency Medicine reported a disturbing trend in the rate of thrill ride injuries.
Overall, the risk of injury is low. Of the 900 million rides taken in the US each year, about 1 in 124,000 result in a significant injury that is detected. Only about 1 in 15 million require hospitalization and 1 in 150 million rides taken results in a death. Most of the worst injuries are from internal bleeding or from brain damage.
As my own children learned while playing Roller Coaster Tycoon, the fastest rides often have the longest lines, creating a strong incentive to build them bigger, faster, scarier.