My commute is short - rougly 2.5 miles one way on a 35mph 2-lane street. I'm driving to work this morning and there is a woman who swerves around the left lane traffic to get behind me. I'm going faster because I don't drive like an idiot: accelerating immediately to 35 when the traffic starts to move and then hitting the brake at the next stop light. Instead, I maintain a speed that lets me minimize breaking - today around 25-30. I'm in the phase where everyone in front of me is braking and hence I'm moving faster than most traffic.
I hear a honk and think nothing of it - can't be to me. Then I hear this lady behind me honk repeatedly and she is looking at me and screaming and flailing. I quickly realize that her goal is to go as fast as possible to her interstate exit (roughly a half mile away) and my lack of desire to share her goal is frustrating her. Note that if I thought it would make any difference in arrival time for myself or this woman, I would have gone 35-40, but it really wouldn't have.
So, Public Service Announcement of the day. If you are on your commute, and are late getting where you want to be - be it an airplane or a meeting, speeding and weaving aren't going to help. You are already going to be late, it is out of your control, relax. Trying to make up time won't work and will likely only increase your commute.
Imagine if I doubled my speed for this woman (25->50) and the traffic / stoplights ahead of me would have let me maintain this speed (they wouldn't). Instead of taking 0.50 miles /25mph = 72 seconds, it would have taken 0.50 miles / 50 mph = 36 seconds. She could have shaved 36 seconds off her trip. All that frustration over 36 seconds. And my assumptions were very generous - in reality, she probably would have saved no time at all because of stop lights and other traffic. Also, she risks me acting like a jerk and actually slowing down (which I didn't do), or getting in a wreck/ticket which will add far more than 36 seconds to her journey.
One last calculation. You might argue that in her case it is only a small savings because of the short distance / road condition / whatever. Lets say you have a 20 minute commute where it is dominated by a fast road (highway, expressway) which accounts for 15 minutes of your journey. Lets say that the speed limit (or traffic speed) of this road is actually 60mph. So, your travel distance is 15 miles. You are late and decide to speed. You really are crazy and can somehow keep up a consistent 75 mph (or think that you can). Now, your commute time for this 15 mile section drops from 15 minutes to 15 miles / 75 mph = 12 minutes. You've saved three minutes off of your commute - again, not appreciable, and again I've given you generous assumptions.
Don't believe me and still think speeding to work makes sense? Time yourself when speeding and time yourself when not. I bet that you will empirically find the difference to be even less significant than the theoretical differences I postulate above. Once you add in tickets and wrecks and try to imagine the time to work as a random variable where you want to minimize the mean, I would claim that driving faster on average makes you take longer to get to work.