oops better correct this,, when "I" commuted, that would be from bolton.... it was long enough driving ...... though normally it was stop-start, was a few years back when they were fixing it....I commute across it now but on the path. I've seen 3 people in my 20 years of living here ride over it on the road and all I can say it you're a lot braver than me! It's so dangerous - 2/3 of people I've seen have been touring (panniers etc) so they obviously weren't local, maybe doing a LEJOG or JOGLE and you can see the fear on their faces. The other guy was doing about 30 on a roadbike (all the gear, sky kit etc) so he wasn't too bad.
I only ride 3 1/2 miles each way but that bridge is by far the worst of it.