I think much of the perceived terror of any road is how fast the cyclist is moving.
Yes. Riding fast makes a road seem much better in traffic. The A49 is a pussycat.
A36, yes, quite nasty.
A303, very very nasty in daytime. I've done it in rain, I got off at the next chance which didn't need a big detour.
A66 is another nasty.
A40 west of Gloucester at 5pm, very bad also.
I've done all of those and others that are just as bad.
But my worst was the A720 Edinburgh by pass when it was legal to cycle on there.
Easily the worst of any road I've cycled on. It's been illegal to cycle on for around a decade now. I bet that the no cycling law is better enforced than the flouted speed limit and poor and dangerous (allthough very normal) driving, which are actualy what make this road so dangerous to cycle on.*
*It had very low usage by cyclists but about 5 cyclists a year died on that road, so I heard/read somewhere.