The 18-mile Triangle Expressway will run from Interstate 40 at Research Triangle Park to Holly Springs. Drivers will pay tolls electronically once completed in late 2012.

Commuters and truckers, weary of rush-hour congestion on I-40, have been eager to see the state build the proposed Southern Wake Expressway from Holly Springs to I-40 near Garner.

There has been less support for the Eastern Wake Expressway from Garner to Knightdale, where it would meet the existing 540 loop.

Traffic forecasts produced by turnpike engineers Wednesday suggest that building the southern section as a toll road would ease congestion on I-40 in Raleigh, and on east-west routes such as Ten Ten Road.

And it would bring more paying customers to the Triangle Expressway.

"Making a business case for constructing a project is stronger on the southern side than on the eastern side," said Steve DeWitt, the turnpike authority's chief engineer.

Joe Bryan of Knightdale, a Wake County commissioner who chairs the Capital Area Metropolitan Planning Organization, hopes the coming study will confirm his belief that the Eastern Wake Expressway is an essential part of the loop. "From a system standpoint it would be very appropriate to have a complete circle," Bryan said.

Wake residents will be involved next year in efforts to choose the best route.

No decisions are expected before 2011 on whether to build the two roads, either separately or together. Local officials and the legislature would have to approve any decision to build the routes as toll roads.