Since you asked
If you're ready for it, here is the most recent Division Order, "Sequential Order of Unit Selection for Traffic Collision Calls (Priority I, II and Ill)" that I knew about. Of course it becomes more theoretical than real a lot of the time. And I don't know exactly how the traffic divisions' "beats" are configured.
"CI" - Collision Investigation unit (T-car); "TE" = Traffic Enforcement unit (motor units and a few "E" units - TE officers in cars) here and there.
1. Any CI or other deployed traffic unit (other CI, TE, etc.) listed on the defined beat in which the call is located.
Exception: A patrol unit from the Area of occurrence shall be the first unit dispatched to a traffic collision call requiring a Code Three response. A traffic unit shall be dispatched Code Two to handle the investigation and related reports.
2. Any CI or other deployed traffic unit (other CI, TE, etc.) listed on an adjacent defined beat (adjacent area) within the bureau of occurrence.
3. Any patrol unit listed on the defined beat in which the call is located. NOTE: The traffic division watch commander shall be telephonically notified prior to assigning Priority-II traffic calls to a patrol unit.
4. A patrol unit (except Basic Car) in the Area of occurrence; whose selection is based on proximity to the location of the call.
5. Any patrol unit in the Area of occurrence, whose selection is based on proximity to the location of the call.
6. A patrol unit (except Basic Car) from an adjacent Area within the bureau of occurrence, whose selection is based on proximity to the location of the call.
7. Any patrol unit from an adjacent Area within the bureau of occurrence, whose selection is based on proximity to the location of the call.
8. Any CI or TE field supervisor listed in the Daily Deployment Plan's miscellaneous field, from the bureau of occurrence.
9. Any CI or other deployed traffic unit (other CI, TE, etc.) listed in an adjacent Area, irrespective of bureau boundaries, whose selection is based on its proximity to the location of the call.
There are two similar orders of selection, one for non-traffic priority calls, and one for non-traffic, non-priority calls.