How do you report dangerous drivers on the freeway?

There is a big white box truck with no markings and almost fully hidden plates driving recklessly on I-45 that is driving aggressively (ignoring merge rules, driving on the shoulder of entry ramp to go around cars, following inches behind other cars, trying to intimidate other drivers.) Calling 911 doesn’t seem appropriate because it isn’t an emergency, but it will probably be an emergency sooner or later. Isn’t there a highway reporting line or something?