Double Decks Bus, Super long Bus, BRT, MTR with 4 doors.
4 doors Mode
Each units of counter only support 2PCS of binocular cameras for 2 doors, so over 2 doors, you must use 2 Units of BPC with 4 binocular cameras to monitor 4 doors. Over 4 doors, you must use more groups to communciate.
In multi-door mode, Unit A will collect Unit B datas, count all 4 doors data and send all of them to server by 3G.
Because two units has different requirements, so counter A must connect 3G network and GPS device, or connect 3G Mobile DVR or GPS Tracker, Counter B doesn't need 3G or GPS function.