The westbound North Circular, from Brent Bridge to Hanger Lane, was on my 5.30am summer 'fast commute' route. Would not have touched it later in the day but it was great for speed!
Oh yes, that reminds me, I think I 'did' Hanger Lane once (I think that's what it was, underpasses etc).. Once was enough.
Shepherds Bush roundabout was pretty horrible until the bedecked it with traffic lights which was a great improvement.
I used to do the A2 regularly, Canterbury to London. Eventually I worked out a quieter route.
I think the scariest is a not so busy and thus fast road with slipways eg Western Avenue extension in London, I didn't dare cross the slip roads so kept going down and up again, and then the A11 between Newmarket and Red Lodge. It was dark and I wimped out at the next exit.
On hols in Stockholm with a 5yo on the childback tandem, ended up going into this myseterious tuynnel with traffic going seemingly ever faster. I hopped off and started retracing. Some nice woman slowed down and said it was OK, the tunnel was in fact very short and I was better off keeping going. We did and it was. Terrifying from a parent pov, would have been fine with just me.