WASHINGTON, June 19 (UPI) -- U.S. motorcycle fatalities in 2006 increased for the ninth straight year -- more than doubling from 2,110 in 1997 to 4,810 in 2006, researchers said.

The report, the "Survey of the States: Motorcycle Safety Programs," by the Governors Highway Safety Association showed that motorcycle fatalities increased in 27 states and Puerto Rico from 2005 to 2006. In 2006, 67 percent of all motorcycle fatalities occurred in 15 states. Also noteworthy is that in 2004, 2005 and 2006 nearly one-third of all fatalities occurred in California, Texas and Florida alone.

The report also said that there is a patchwork of helmet laws, scant enforcement and a lack of helmet promotion despite clear evidence that proper helmet use saves lives. In states with partial laws or without helmet laws, most riders who died were not wearing helmets.

Motorcycle sales almost quadrupled from 1997 to 2006, from 356,000 to almost 1.1 million and as a result, 29 states and the District of Columbia indicated they have delays ranging from one day to 12 weeks for training classes.

The report also said that in 2006, 25 percent of operators in fatal motorcycle crashes did not have a valid motorcycle license, compared to 13 percent of drivers of passenger vehicles.