Im on my phone at the mo, so cant see the map, but will have a good look at it.

The county border runs south from the Washington Highway/Lambton Estate as far as roughly Rainton Meadows - Tyne & Wear being to the East and Durham to the west. Road crossing points carrying 'Welcome to' Co Durham/Sunderland are on the A183 bridge just past the old Lambton Garden Centre, Fencehouses Crossing and the bridge off Blackie Boy Road at Chilton Moor.

The metro could go as far as Fencehouses in the south staying in Tyne & Wear (depending where they site a station), but there is the possibility to go on the line from South Hylton and go right over the viaduct as mentioned earlier.