Thankful for you and your son that you were prepared.
Glad things didn't go differently. Road rage is a very real threat that can affect anyone. It is easy to forget that driving in traffic is a social interaction where you deal with hundreds, and even thousands of different people. We all hope that everyone is just trying to get where they are going, but you just don't know what another persons state of mind is. Unlike when you decide not to go to certain neighborhoods, or areas of the city because they are unsafe, The highway isn't an environment you can "control". Everyone drives on the highway- from regular citizens to murderous criminals.
When someone uses a multiple ton vehicle to threaten harm to others, and it comes to a confrontation I don't find it unreasonable at all to introduce a firearm into the equation as a means of protection.
my best to you,