Dispatch is easy to hear. They transmitt from tall towers with high powered radios. The cars are harder because they only have antennas on the roof of the car and transmitt with less power. But you can still hear them when you are with in a couple of miles of their location.
The Parkway channel [155.460] is used by both the dispatcher and cars, and uses the same PL tone [110.9]. As far as 173.075, isn't that the frequency for the Lo-Jack car finder system?
Anyone who would sacrifice Liberty for security, deserves neither. Ben Franklyn