RALEIGH, N.C. — Area transportation planners are looking to the middle of the road to help solve the region's traffic congestion problems.

The North Carolina Turnpike Authority and the Triangle Transit Authority have reached a preliminary agreement to reserve the median of proposed toll roads for future mass-transit projects, from carpools to buses to trains.

The Turnpike Authority will design toll roads with a 78-foot median, almost three times the 30-foot median in place along the section of Interstate 540 under construction between Interstate 40 and N.C. Highway 55. Officials said the most likely spot for the wider medians would be on I-540 between Research Triangle Park and Holly Springs.

"Getting this median, it could mean that we create lanes with reduced or no tolls for buses or van pools, even car pools. But it could also mean that they're designed in a way that you could come back later and put a fixed guide way bus system or a rail system," said Wib Gulley, the TTA's general counsel.

The two agencies still need to determine how the sprawling medians will affect the cost of building the highways and whether it would adversely impact the amount of toll revenue collected.

The TTA last month dropped its plans to pursue federal support for its proposed $800 million, 28-mile regional rail system because it couldn't meet guidelines for daily ridership. Still, officials are keeping rail as a transit option for the future.

"It's the people in Raleigh and Wake County, for the most part, that are going to be paying for these toll roads, and if we can put mass transit in the corridor, I think it's a good idea," said David Joyner, chairman of the Turnpike Authority.