I'm really enjoying the eyecandy vehicle set! The way I use it, it does have a bit of a practical aspect, too.
Police cars are sent to various bus stops in cities, as if they are part of a company in-house transit security force. While I am aware that I can set them up to never load passengers, I do allow the police cars to transport passengers anyway. The revenue generated, I treat as if it were fines given out to vandals or those trying to avoid paying fare.
Generally I do not have the police cars follow routes that buses use, but instead make them seemingly random patrol. This is done by a long set of orders that complete a loop three or four times in different order of stops.
Example:
Is the normal bus route.
Police cars may be set up as:
Ambulances are handy, too, especially with the Total Town Replacement Set, which features hospitals. Around here, there are private-run medical transport services. Often these companies use ambulances that were phased out by city emergency services. In my town, if you get injured and city fire department EMTs come, they have to transport you to the closest hospital that is appropriate to your needs. Closest to my last home was a hospital with a reputation for being poorly run and patients that left in worse shape than they came in. One would need to arrange for private transport to be seen elsewhere.
Who says TT can't also allow for medical transport as such? Set up a bus stop by each hospital, and use the ambulances for such a system!