Purdue University researchers found that an increase from 65 to 70 mph on Interstate 65 was still safe, a result that adds to mix of research results nationwide since passage of the National Highway System Designation Act of 1995, which gave states freedom to set interstate speed limits. Study authors acknowledged the ongoing debate in a Purdue University news release.

"These findings are important because the influence of speed limits on roadway safety has been a subject of continuous debate in the state of Indiana and nationwide," said Fred Mannering, a professor of civil engineering.

Most research studies have concluded that lives have been saved by the 1974-mandated 55 mph interstate speed limit, a result that has been confirmed by some research looking at recent speed limit increases on interstates.