Arched Bridge

snapper21

Have a request for an arched bridge and I've layed out a design I thought I'd throw out here for critique. Feel free to chime in with any flaws that I may have overlooked, or possible add ins that may help the process/structure. It's a basic structure that's wanted so any flowery add ons are not necessary.
12' bridge. Largest apparatus that wil cross it is a kubota rtv900 with a 60" W.. Homeowner wants 62", and yes I agree, the pickets will take a beating I'm sure, but I added into the design just for that purpose.
Post and beams- 4x4's below frost, 3 posts per beam(approx 20 5/8 oc). Beams-doubled 2/10's inset in post w/ bolts. Maybe 1 1/2" inset.
Outside arched band (this will not rest on the beam, but the scabbed 2x10 on the inside of it will. arch is from a 58' radius and will be 4" rise in the middle. Band will be 2@2x12's stacked creating an 18 1/2" band. A 2x10 will be scabbed to the inside of this band, with the arch that I cut out of the bottom of the 2x12 fastened to the top of it to recess 5/4 below the top of the band(so that treads will be flush with band. Think I confused myself with that explanation, but read it slow and it comes together. Other side will be identical of course, and the joists between them will be 2x12's cut with top arch to support the center of bridge.
Hand rail will be 5/4x6 decking board, and 1x8's will have the same rad. arch cut in them and will be used to sandwich the pickets beneath the rail ( I'm thinking I need to dado the bottom of the rail for the 1x8's to sit in). For purpose of easy reinstall of pickets when the HO knocks them out I am going to use 2x2's layed horizontal between the 1x8's to create a pocket to slide the 2x2 pickets up into. No fasteners will be used on them. They will be screwed directly into the side of the band at the bottom, and a 1x8 cut at arch(identical to piece under hand rail) will be used to pad out the band to take them, since they will be that distance out from the band at top. There will be 4 posts for the rail, with the outside posts sitting back 12" from the end of the bridge.

This is my first bridge, and I haven't seen one arched for use of heavy equipment yet. Therefore I ask,,,,,, would you feel safe driving on it?
Edit
No arches will be cut out of the joists. They will be fastened just above the arch on the band. The only part of the joists that will be cut off is the very top corner of each side.