Originally Posted by Schrauf
It's not bad at all. Maybe a little dicey if you try to punch it at 25 mph like I do on the downhill when the sidewalk is wide open, but take your time and you will have no issues.
One side is a little wider than the other, but I can't remember which (I think southbound, although people go in reverse all the time, so if you find the wider side you can use it for north or southbound).
I disagree, at least in part. If it's a wide trailer, you'll definitely have trouble heading north to Vancouver. I haven't ridden SB, so I don't know what that side is like. Going NB, on the downhill you'll need to watch out for some large electrical equipment cabinets and the gear that closes off the sidewalk during bridge lifts. On the NB side, it may be narrow enough to give a trailer problems. I agree with Schrauf that you'll definitely need to control your speed on the downhill.
I highly, highly recommend NOT going against the "normal" flow of traffic. People may go in reverse "all the time", but most riders aren't expecting that, and I can't think of much more frightening that having to squeeze by someone towing a trailer at 15+ mph the wrong way on a bridge full of metal protrusions and support beams.
The northbound side of the I-5 bridge looks like this: