glad you're not the only one.

it is definitely a bug. supposedly some sort of anti-exploit controls how many ambulances/fire trucks/streetcars etc that can be in your city at a given time. it totally backfires to the point where oil trucks weren't delivering to my power plant, ambulances completely ignored injured sims, and fire trucks sat idly by while buildings burned down.

I really really hope EA/Maxis are addressing this and working hard to find a fix.