I've been looking for a game which does a really good job at letting someone design a transit system and then just letting it run--making adjustments from time to time to make money.  Ideas?

I tried Traffic Giant and it doesn't work on my computer.

These might not be exactly what you're looking for, but perhaps they're close?

http://www.makeuseof.com/tag/two-free-transport-simulator-games/

Yeah, I tried them, no luck

In it's day, Transport Tycoon was amazing, but it's a bit dated these days.

It's bus management is excellent, but only ends up making a small amount of the game, because you just don't make enough money from them.