It seems that ccomley is asking for an AI that could set service in depot between cities. Currently there are two AIs: StreetTraffic1 and TownCars
. The former is abandoned and buggy. The latter is developed by Zuu. In its thread he wrote that depots are destroyed after populating to the maximum to reduce the expenses to zero (depots pay maintenance). You could ask there for a new option to keep depots and build them automatically once per city.
Ah! Not quite but close! I'll take a go at TownCars. The thing about StreetTraffic is the cars all try to stay close to their original depot, I presume because they keep popping in for a lube job. So they don't spread around the map. If there ARE no depots, maybe they'll spread!
You can always solve the problem of a bankrupt AI by sending it some money of course - depends why you're playing it.