Why the hell is your maintenance cost so high?!?!?! A stabilised earth embankment with suitable drainage will last ages. If you are having to retain it you have done it wrong. The whole idea of an earth ramp is that it has settled to its natural angle of repose. Planting some grasses and initial covering with a geo-membrane is all you need to do.
Maintenance of the bridge is going to be tiny. You would have regular yearly inspections checking for concrete cancers and cracking but thats about it.
Maintenance of a level crossing on the other hand is continuous. The bituminous surface will spread under the loads of cars and trucks, this will push the surface closer and closer to the rail. This has to be continuously cut back otherwise bad things happen. The rail cutting also acts as a water channel causing the sealed surface to break up.
As for the lawsuits that is never something you can control for.