Why are there Traffic Jams?

(Cathy) I had to take the older one to our doctor for a check-up today. The appointment was for 3pm. It was raining so I gave us one hour and ten minutes for a 25 minute drive! I thought that would have been enough time with extra time built in. Well, we were not late, just exactly on time. We were at the doctors office for 30 minutes. The traffic was a lot worse going back home. Traffic in this city is nothing new. It's just that while you are sitting, idle you have time to contemplate the why. What causes traffic? Is it bad drivers? Is it a domino effect from one driver applying the brakes? When you think about it, if everyone drove at a consistent speed and respected turn signals and allowed people to merge we would all get to where we wanted to go a lot quicker. Do you agree?