Driving causes bad moods

Two weeks ago I took the bus to work. Actually, first I took it to the gym, then to work, then home. I was feeling quite relaxed walking home from the bus stop. When I got home, I had to get in the car to run an errand. I noticed immediately how uptight and exasperated I got. I was yelling at someone in front of me (who, of course, couldn't hear a word I said) because they were going only 25 in a 35 mph zone. Ridiculous. It was shocking how just getting in the car changed my mood and composure.