Road surface under the bridge influences truck's maintenance

That's intentional (beceuse the surfeces intentionaly do reduce
the maintenence requirements), but what isn't is the fact that the
brige is "transparent" to this & doesn't do the same as surfaces.

See more in exisitng isse report here: Trucks consuming different Maintenance amount on roads (Bridge and crossings)

I feel like bridges should count as surfaces by default - It's clearly a paved asphalt road

I suspect that the “surfaces map” is 2d like the pathfinder, so marking the bridge as a surface on that would mean that everything below the bridge was also treated as a surface. Probably need to adjust the maintenance calculation to account for whether or not the truck is on a structure (bridge or ramp) and ignore the surfaces map if they are.