PLEASE DO NOT attempt to access the cache from the West Charlestown Bypass (A37), this is dangerous and will not be successful - it isn't up there... Access the cache on foot/bike along the Great North Walk.
We have a little series around Newcastle, based under/over major roads, but not on them, which we've based on a similar series from the North Coast. We've always wanted to place a cache here, long before this series was started... The cache is about 40% of the way into the tunnel starting at the eastern side, and is magnetic. Watch the terrain and attributes for help!
The GPS was a bit sad at GZ, so coords are based on averages from either side - use the hint and attributes, watch your footing, and stay off the road!