Final answer:
Local law enforcement must contact their state or regional transportation department or traffic management center to activate the dynamic messaging system for public information.
Step-by-step explanation:
When local law enforcement agencies need to activate the dynamic messaging system, which is part of an intelligent transportation system used for communicating important information to the public, they typically must contact state or regional transportation departments or the specific entity responsible for traffic management and control in the area. This might be a state Department of Transportation (DOT), a toll authority, or a traffic management center (TMC). These organizations have the authority to control digital signs and disseminate critical alerts such as AMBER alerts, severe weather warnings, traffic conditions, and other emergencies.