My daughter asked why I always honk twice in the carpool lane but never actually leave the car running

My daughter asked why I always honk twice in the carpool lane but never actually leave the car running.

Punchline

I told her the first honk is a greeting, the second honk is a reminder that we're Very Busy People, and turning the car off between honks saves gas. It's called tactical idling. She said that's not a thing. I honked again to prove my point.