A patchwork of state laws leaves many areas where drivers can choose not to buckle up, with little likelihood of being stopped. Only 18 states have laws requiring seatbelts for both front and rear occupants and categorize not wearing them as a primary offense — meaning drivers can be pulled over for that alone. In 15 states, failure to wear a seatbelt in front seats is only a secondary offense — drivers cannot be given tickets unless they are pulled over for other violations.

“It’s still the same things that are killing drivers — belts, booze and speed,” Mr. Adkins said.

About half of all traffic fatalities involve unbelted occupants, and almost a third involve drivers who were impaired by drugs or alcohol, according to data from the National Highway Traffic Safety Administration, the federal government’s main auto-safety agency.

In Alabama, steady budget cuts have resulted in a decline in the number of troopers patrolling the state’s 103,000 miles of highways. David Brown, a research associate at the University of Alabama’s Center for Advanced Public Safety, studied the state’s 2016 traffic fatality reports and found an increase in fatalities involving high-speed crashes.

“Total crashes were up less than 5 percent, but fatalities were up 25 percent,” he said in an interview. “I think speeding is the No. 1 problem. There are times of the day when we only have one or two troopers on duty in a county, so you can speed, and there’s no one there to deter it.”

In some states, highway speed limits are rising. In recent years, Texas has increased speed limits to 85 miles per hour in some rural areas. About 1,500 miles of roads have a limit of 75 miles per hour or higher.

In the fall, the N.H.T.S.A., the National Transportation Safety Board and several nongovernmental organizations, including the National Safety Council, began the Road to Zero initiative to eliminate traffic fatalities within 30 years. The effort places heavy emphasis on the promise of autonomous vehicles.

But others say that more needs to be done now on basic road safety issues. “The way to bring down the rise in deaths is with a wide range of the nuts-and-bolts measures, not self-driving cars,” the consumer advocate Ralph Nader said in an interview in October.