A 500-mile bus rapid transit network operating in HOT Lanes from Frederick, Md. to Prince William County, Va. could be reality within 30 years, according to a study by the Metropolitan Washington Council of Governments.

The proposed bus system would operate primarily in express toll lanes on the region's interstates, explained Transportation Planning Director Ron Kirby. The buses, which are "somewhere between a regular bus and rail," would run every 10 minutes during peak hours and every 20 minutes during offpeak hours.

Some parts of the interstate system, like where Virginia is already building HOT Lanes on the Beltway, would not require any new construction. In other areas, existing HOV lanes would be turned into express lanes and additional lanes may be added.

The costs for constructing the project -- which have been estimated to be as much as $3.5 billion a year for 20 years -- would be covered by taxpayers, along with toll revenue and fare revenue.

"You could get this whole network built by 2040, no doubt about it," Kirby said, emphasizing that the study would need the approval of area governments to leave the drawing board.

And for the system to be successful, all three jurisdictions would need to participate, he said.

The D.C., Maryland and Virginia departments of transportation could not be reached for comment.

The proposal, "as a long-term strategy, is right on the mark," said Fairfax County Supervisor Jeff McKay. "We're going to have no choice but to come up with other solutions to our long-term congestion."

But even some fans of BRT are skeptical that a highway-based system makes sense.

The system would be more effective if it connected to an off-highway network, said Montgomery County Councilman Marc Elrich, D-at large.

As proposed, the system doesn't encourage development around stations the way Metro rail does, said Stuart Schwartz, executive director of Coalition for Smarter Growth.

But AAA Mid-Atlantic spokesman Lon Anderson called the system an "outstanding" concept, as long as it doesn't take away lanes from other drivers.

"BRT is going to be the future of mass transit," he said.