ARLINGTON, Va. -- Higher speed limits are killing thousands of Americans, according to a new study out this week.
Police Capt. Thomas Didone sees the danger of speed daily in Montgomery County, Maryland.
"Speed is a determining [factor] whether a crash is an injury or a property damage," Didone told CBS News. "The faster someone's going, the more likely that someone's going to get hurt."
But for Didone, it's also personal. His 15-year-old son Ryan died in a crash where the driver was going at least 20 miles over the limit.
"If he had been going the speed limit, there's not a doubt in my mind every kid would have been home safe," Didone said.
But speed limits across the country have been going up since the federal government repealed the mandatory maximum of 55 miles per hour speed limits in 1995.
The Insurance Institute for Highway Safety found those increases have caused at least 33,000 deaths over a 20-year period.
With every five miles the speed limit rose, deaths grew by four percent. On freeways, they jumped eight percent.
"For this few minutes that you're saving by going faster, you're increasing your risk quite a bit," said Charles Farmer, who authored the study. "There are people dying out there."
But the National Motorists Association says speed limits work best when approximating the natural flow of traffic, which may be higher than the posted limit.
"The fatality rates overall have dropped dramatically to the point where, in the last couple of years, they're the lowest on record," the NMA's Gary Biller told CBS News. "So as states have continually been raising speed limits, their safety statistics have actually gotten better."
Researchers estimate 1,900 deaths in 2013 were due to the higher speed limit -- that's almost as many as lives saved from frontal airbags that year.
Seven states have speed limits of 80 or higher. In some parts of Texas, it's 85 miles per hour.