start on the old a303 (unclassified), 1.1 miles east of parkhouse corner at “s - bend” road sign 200yds before passing under a303(t). (gr su253441) proceed east to join a303(t) at thruxton airfield. leave the a303(t) at a342 slip road to turn at rbt (5.66m)(gr su340459). take 5th exit to cross over a303(t) (caution - two way traffic on bridge). after crossing bridge take 3rd exit from rbt to rejoin a303(t) westbound. leave a303(t) at thruxton circuit/quarley exit to finish 30 yds before the road sign which is 100 yds before the t-junction (gr su273446).