Why are Houstonians bad and aggressive drivers but so chill otherwise?

This has been confusing me:

On the road, Houstonians are terrible drivers. Aggressive, reckless, impatient, and psychotic. But once you’re off the road, the majority of people I’ve met here are super chill and genuinely friendly.

How does that work?! How can people be so nice in person, but turn into complete menaces behind the wheel?