 An additional arch was added to Skerton Bridge in about 1849 to allow for the passage of the " Little " North Western Railway ( since closed ) beneath it . The bridge continues to be used by heavy traffic . A survey in 1995 concluded that the bridge is still strong enough to carry vehicles ten times the weight of the heaviest vehicles of the time it was built . Grosvenor Bridge remains in use , carrying the A483 road over the River Dee , and is still the longest single @-@ span masonry bridge in Britain . 
