Vehicle Maintenance Discount Not Applied on Bridges

Issue description

Whilst driving on placed surfaces, vehicles receive a 20% maintenance discount; presumably the logic being an artificial surface is better than raw ground.

By the same logic, vehicles on traveling on brides should also receive this discount. At present, they do not.

An interesting note; if a bridge passes over the top of a placed surface on the ground beneath the bridge, the vehicles momentarily receive the bonus from that surface.

Reproduction steps

1. In any game with a bridge (both cable stay and truss tested) over land, build a surface partially underneath it.
2. Observe a vehicle as it transits, watching the maintenance usage rate indicator as it goes.

The images below are an example of this

A save game with the relevant structures is included.

Game version and build number

v0.8.1a (b550)

Operating system

Windows

Attachments

Save 2026-03-12, 21-36-09.save

Also note that a similar effect occurs on railway level crossings; if a surface is built under them, full bonus is applied during the transit and if not, the bonus is momentarily lost.