This one is difficult to master if you're a nervous driver who is always on the brakes. What you need to understand is that your tail lights are your only real form of communication with those behind you. If you're constantly tapping the brake - or worse - driving with your foot on the brake all the time - it's like crying wolf. The driver behind you has no indication of if you're really slowing down, or just nervously tapping the brake for no reason. When you do need to stop, everyone behind you is conditioned to think you're just nervously fiddling with the brake pedal again, and that's one way to ensure being rear ended.
So what do I mean by "don't use your brakes"? Simple - take your foot off the accelerator. Your car will naturally begin to slow down. If you're not slowing down enough, then you may use the brake. But if you're in motorway traffic and the brake lights come on in front of you, just take your foot off the accelerator first. Chances are the person in front is a nervous braker. 9 times out of 10, a slight slow down on your part will be all that is needed, and because you didn't brake yourself, you've not amplified the problem for those behind you.
Why drive like this? Well - a good deal of traffic jams are known as phantom or shockwave traffic jams. The traffic is stopped for no other reason than a nervous braker. It works like this - someone gets a bit twitchy and instead of simply reducing their speed with the accelerator, they dab the brake. The person behind them does the same, only a fraction harder. Behind and to the sides, people now see two brake lights so they all begin to dab the brakes a little too. Each dab of the brakes slows down the traffic in that lane by a tiny fraction until suddenly, a kilometre behind you, everyone has come to a complete stop. There's your phantom traffic jam. If you were able to observe this from above, it looks like a shockwave travelling backwards through the traffic. In effect - particles bunching up and pulling apart. Remember the river analogy from part 1 of this series? If you want to see this in a mini simulation, this little java application can be tweaked to show the problem very clearly : A Microsimulation of road traffic. Set it to 'ring road' and watch what happens - you don't need to tweak anything but after a few seconds you'll see a shockwave traffic jam form. Think about this next time you're driving.