Nice tip! I'm up that way this weekend
Incidentally, it's also on a 'bus route:
By bus, the services 222 and 220 regularly leave Park Lane in Sunderland, or the bus station in Durham and set down at the nearby Mill Inn. There's a short walk under the A690 continuing until you reach the last roundabout of the industrial estate. The entrance to the Reserve is called Mallard Way.