Fatalities increased by more than 50 percent on highways where the speed limit was increased to 65 miles per hour, according to a survey of accident statistics from 22 states.
Officials of the National Highway Traffic Safety Administration cautioned that the findings, which cover only a three-month period, may not justify drawing long-term conclusions about the effects of the higher speed limits on highway safety.
The 22 states were among the first of 38 states to increase their speed limits to 65 mph on rural interstates last spring after the change was permitted by Congress.
According to the figures made available by the NHTSA, 450 people were killed on rural interstates from May through July in the 22 states.
Separate statistics from seven states where no speed limit changes were made showed that fatalities increased 10 percent.
Rep. James J. Howard (D-N.J.), who strongly opposed the legislation to raise the speed limit, called the figures "an unacceptable increase in deaths and injuries."
Others were not as certain about what the figures showed.
"We don't know what the reason is behind these numbers," NHTSA Administrator Diane K. Steed said. She cautioned that other possible factors have yet to be examined, such as a sharp increase in the number of vehicles on the road or the effect of alcohol use by motorists.
Steed also noted that no information has been gathered on how fast motorists were traveling on the highways where the speed limit had been increased. She said that in five of the 22 states -- Montana, Oklahoma, Washington, Colorado and West Virginia -- the fatality figures declined.