Try this simple 1 minute meditation to calm the nervous system and slow down your breath. It's especially effective for sitting in traffic.
Start by bringing your attention to your breath.
Notice your breathing in, and notice that you're breathing out.
As you inhale, say to yourself, "I am calm."
As you exhale, say to yourself, "I let go."
Continue a few more times. Watch as your breath slows down and the words get softer in your mind.