I can confirm the southbound side appears to be about a foot wider than northbound. This is odd because I thought northbound was the newer of the two spans.
Bikers going against the flow should yield by stepping off to the side between the beams, where even northbound there is plenty of room, unless maybe two wide trailers pass each other. Even in that case I think there is room, but I don't know trailers well.
Of course, the biker going against the flow does not always yield - there is occasionally someone who thinks they have the right of way because they are going uphill, because they are old, or because they are wearing pink underwear.
Originally Posted by Matt P.
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: