Engineers --> Bridges --> Armor?

[Mr Grumpy]

Yes the units would gain the movement advantage of the road in that hex, so the best possible situation is to find a hex next to a river with a woods (or other defensive terrain) hex with a road running through it, the woods will provide a defensive benefit for the bridge engineers and mechanised units could then move in T mode along the road through the wood hex and then over the bridge.

It is also worth considering the terrain on the other side of the river as you would not want to prevent your mech units being able to exploit the crossing.