The River Test runs along the western border of the city, separating it from the New Forest. There are bridges over the Test from Southampton, including the road and rail bridges at Redbridge in the south and the M27 motorway to the north. The River Itchen runs through the middle of the city and is bridged in several places. The northernmost bridge, and the first to be built, is at Mansbridge, where the A27 road crosses the Itchen. The original bridge is closed to road traffic, but is still standing and open to pedestrians and cyclists. The river is bridged again at Swaythling, where Woodmill Bridge separates the tidal and non tidal sections of the river. Further south is Cobden Bridge which is notable as it was opened as a free bridge (it was originally named the Cobden Free Bridge), and was never a toll bridge. Downstream of the Cobden Bridge is the Northam Railway Bridge, then the Northam Road Bridge, which was the first major pre-stressed concrete bridge to be constructed in the United Kingdom. The southernmost, and newest, bridge on the Itchen is the Itchen Bridge, which is a toll bridge.