The A47 Acle straight between Acle and Great Yarmouth.
It was near the end of a week long cycling holiday around East Anglia with a friend and his dad (we were only 13/14 so needed an adult with us). Started the day in Kings Lynn so what nicer way to end a 70 mile day than having huge lorries roaring past you for 5 or 6 miles - I hadn't had any input on the route planning (I did the next trip we did).
Whoever planned that for kids is a bloody moron, accidents are very frequent on that stretch.
For me,
A40 Witney bypass as a foolish yoof
A10 from waterbeach to the next junction, only a mile but that was long enough
Crossing J41 of the m6 and then the A6 into Penrith
The single lane with passing place that was the main road between Tobermory and the ferry port, not frightening, but five tour buses in a line behind me just made me feel very uncomfortable.
Should I add the A142, site of my smidsy? Difficult to entirely avoid fast a roads round here, even if just to cross them. The roundabout at Cambridge airport being a great example where you have to cross the fast moving traffic to stay on the segregated cycle path because its only on one side of the road. Further back there's an excellent underpass to cross the A14.