I'm guessing that HTC wouldn't allow it, but the map I'm working on only has one train going to the city/strat complex, and the radius is set to cover all the strats. I'm guessing that would keep the strats down longer, since there's only one train to supply everything.
If I have to have one train for each factory, I'll have to redo some of the terrain...that would suck because I really like how my strats fit right now and there isn't room for 5 separate trains for one or two of my strat complexes.