Simplex, outside, mostly line of sight, would cover quite a good distance. Plenty for running parking, I would think. If it was stretch out over a couple of miles among taller buildings, etc., then it might suffer on the farthest distances but likely those talking are within certain parking areas. Again, some of this is just assumption on how they're using the radios.
Sounds like the best way to figure it out would be take a scanner in close call mode and see what it hits on, making notes of what you hear and the frequencies/tones being used. Part of the fun of scanning.