In an agreement that echoes toll road and highway financing but is rare to the freight railroad industry, the state of Delaware will completely fund the rehabilitation of a Norfolk Southern Corp. bridge with reimbursement over a 20-year toll period. The Delaware Dept. of Transportation and the railroad last month announced the planned $13-million rehabilitation of the 725-ft-long Shellpot Bridge, which crosses the Christiana River in Wilmington and has a 242-ft moveable swing span. Conrail, now jointly owned by NS, discontinued service over the bridge in December 1994 when the concrete foundation, which replaced timber piles in 1951, could no longer support heavy freight trains. Since that time, freight trains operating in Wilmington have had to run on Amtrak's Northeast Corridor. Delaware DOT spokesperson Michele Ackles says the state is conducting foundation tests and has not hired a designer or contractor yet, though completion is expected by 2003. NS spokesman Rudy Husband says the railroad may consider similar agreements for rehab projects throughout its 22-state network.