Virginia's utility watchdog has promised an investigation into the toll rates on the Dulles Greenway.

The price for riding the privately owned, 14-mile road west of Washington Dulles International Airport is too high, said Del. David Ramadan, a Republican who represents parts of Loudoun and Prince William counties and who requested the investigation.

"This is a major issue for my constituents," Ramadan said. "They drive one mile, they pay $4.90."

The State Corporation Commission, which oversees pricing for utilities and other entities that serve the public, said it will investigate whether the Greenway tolls -- which can reach $5.90 for cars during peak periods -- are discouraging drivers from using the road, which is against Virginia code. The commission could force the Greenway to alter its toll rates if it finds they are too high.

Ramadan said he first tried to work with the Greenway to have Virginia pay for distance-based tolling, but that effort fell through.

"It was a long cat-and-mouse game that they played. They're not really interested in doing any distance pricing," he said.

The agency just approved a 10-cent increase for the toll road, pushing up rates for cars as well as for trucks -- six-axle vehicles now pay as much as $20.80 to use the highway.

"Trucks are not getting on the road anymore, and they're using the 25 mph neighborhood roads, to avoid the road," Ramadan said.

A spokesman for the SCC said he did not know how long the investigation would take. Ramadan said it will involve public hearings in both Loudoun County and Richmond.

The investigation comes as another Loudoun lawmaker is pressing the state to buy the highway -- a potentially billion-dollar endeavor. Del. Joe May, R-Leesburg, is leading informal negotiations with the Greenway owners to see if the state can take over the road, while he pushes legislation through the General Assembly that would allow the state to issue bonds for the highway.

Ramadan said he would support buying the Greenway if the state could institute distance-based pricing and keep tolls low.

"The devil is in the details," he said.

The Greenway owner, MacQuarie Group, declined to comment.