What baldeagl said, set up an ambush for the train at any strat object with objects destroyed. Train will come along to fix them shortly. Watch the Ack!
Convoys do the same for towns, kill some town buildings and wait, or back track the road to find it. Both give you very nice perk points for moderate ammo/ord use.
Tip, kill engine, lead truck first, rest should be sitting ducks.