OS Landranger map number 162.
Start in middle of bus stop layby opposite start of the splay for the opposing layby (GR ST 69594 96432). 
Proceed north on the A38 through Berkeley Road and over the railway bridges to the Slimbridge roundabout where turn (5.3 miles).
Circle and retrace south on the A38 to finish on opposite side of the road to a bus stop just south of Newport (GR ST 69836 97078) approximately ¼ mile before the start.

Organisers should check bus timetable to ensure that starts are not interrupted by buses
Route 62: 10:17 hrs, Route 207: 08:07 hrs, x6: 07:43 hrs
https://citymapper.com/bristol/bus/stops/BristolStop_SwanleyLane_SW_1