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Whenever I'm in my car my phone is plugged into a charger and connected to the car audio system through BT. If ever in such a situation I would simply ask Siri to call 911. I also doubt that any raised monster car would have the mobility or the gearing to keep up with a well maintained car with a reasonable acceleration capability.
I believe your brothers situation was almost completely avoidable.
How?
1. Preparedness - your brother was on a stretch of interstate with sparce traffic. Given the info we have it is reasonable to assume that he had the advantage in acceleration and maneuverability. I am a strong proponent of tatical defensive driving training. Even if your brother was at a disadvantage, even the most basic training should have allowed him to escape the situation. Always make sure that every piece of equipment that you depend upon is well maintained and functional. This includes your weapon, your automobile, and your means of communication. If your brother had connected his phone to a charger when he got into his car his phone who have been operational when it was needed most.
2. Awareness - The first sign of aggression is the time to react and take defensive action.
3. Deescalation - In a road rage situation it is imperative that you do not engage the individual. Your brothers one finger salute threw gasoline on the fire. Most of these situation defuse themselves by simply ignoring the individual wanting attention.
4. Communication - not only should your brother have been the first to call 911, the call should have been placed long before he pulled his weapon and before he even thought about texting anyone.

Hind sight is 20/20, but in most situations you will avoid the horns by simply refusing to mess with the bull. I do hope that your brother's situation is quickly resolved and he along with others learn from his mistakes.
As far "this little community sticking together"...not sure how that applies.