As far as I know the easiest way to tie to a bridge is as follows.
1. Tie a rope to a smaller dock pad for throwing.
2. Throw dock pad and rope past the bridge post on the up wind side.
3. let the wind blow dock pad and rope down wind of the bridge post.
4. Use an electrician's "gopher pole" to reach out and catch rope and dock pad.
5. Pull rope and dock pad to boat and tie off as needed.
Additional dock pads may be necessary between boat and bridge post.
A gopher pole is a collapsible pole that extends out to up to 27' depending on which model you purchase.