SALT LAKE CITY — Utah officials want to start a test program to tax drivers based on the miles they drive, instead of collecting the revenue at the gas pump, in anticipation of more people driving fuel-efficient and electric cars that were expected to dry up the tax money in several decades.

The state already collects fees based on road use through an electronic toll system on Interstate 15. Drivers are billed by a third-party provider, and the money helps repair roads.

With more drivers taking fewer trips to the pump, Adrian Moore, board member of the Mileage-Based User Fee Alliance, said it is crucial to begin looking at ways to ensure electric and alternative-fuel car owners are contributing their fair share.

“When 50 percent of the fleet is electric, there’s just not going to be enough gas tax revenue to maintain your roads,” he said. “In the long run, something is going to have to replace the gas tax.”

The Utah Department of Transportation will be looking for about 100 volunteers to participate in the pilot program funded through federal research dollars, officials said Wednesday.

To avoid using costly electronic monitoring, the selected participants will mostly report their own travel over a year, said Carlos Braceras, the department’s executive director.

He hopes the program will reveal issues that the department would need to address before it could roll out statewide.

“It would just be purely research,” Braceras said. “It would focus in on some key questions and see if we can provide another building block to this puzzle.”

Officials in Oregon have tested three similar pilot programs, and California, Colorado, Hawaii and Washington state have either started experimenting with their own or plan to.

Utah officials expected the pilot program will be ready to launch by next year. State lawmakers welcome the experimentation but do not think a full program will be implemented in the near future.