All of those talkgroups are very much active except GROUP 1 which are the old TG's from svereal years ago. GROUPS 7 and 8 are the most active as you hear supervision talking amongt themselves and the command center. You cannot hear buses talking to supervisors and vice versa on these TG's. Alot of the transmissions in this system are I-CALL's.
Buses have an ICALL like 71XXXX where the x's are the bus number. Supervison handheld radios have either 740XXX or 741XXX and the base stations at the East New York Command Center are designated 7000XX. Usually there are two or three depot's worth of buses logged into a console. If you enable I-CALLs on your radio, then you should hear a wealth more information.