Tailgating, Queue Theory and the "Phantom Traffic Jam"

Yesterday it took me an hour to get to work, a trip that normally takes about 35 minutes. I say "normally" but it turns out there's probably almost never a "normal" day, as I drive a stretch of Interstate 4, a six lane highway that runs from Daytona Beach in the east, all the way to Tampa on the west coast of Florida. I grew up in New York City, but I gotta tell ya -- Florida drivers are the absolute worst on the fyookin' planet!

The reason for the delay? Tailgating accident. There is something about getting into 3,500 pounds of metal that has a decided effect on many people's personalities. Normally docile human beings become overly aggressive. The automobile becomes an extension of our "personal space" and anyone who invades this space is to be defended against. Tailgating 10 feet behind the rear bumper of the car in front of you at 80, sometimes as high as 90 miles per hour won't get you there any faster, in fact, as about six drivers found out yesterday, it often ensures that you don't get there at all! Yep, six cars and SUV's, all neatly parked on the side, almost all of them except the guys in the very front and back with both their hoods and their rear ends completely smashed to smithereens. Obviously, there was no QA Department to test their brains before deployment into production...

Over 95% of motor vehicle accidents involve some degree of driver behavior combined with one of other factors.

My brakes work the same regardless of how close the people in front of me are to each other. If somebody passes in front of me, I've learned to turn down the temperature and just drop back to a safe distance. Unfortunately, some motorists "just don't get it" and the only thing you can do is be extra alert and careful - and give yourself PLENTY OF ROOM to stop safely.

So called "phantom traffic jams" are actually caused by a vehicle braking sharply - causing a red light domino effect. The red light is the brake light that the following driver sees ahead. The driver behind then brakes suddenly and this has a domino effect until further down the line traffic can actually grind to a complete halt.

We as programmers understand the math behind this as it is a textbook case of queue theory in action.

Motorists are then perplexed as to what has caused the traffic jam. In reality they have all caused the traffic jam because of their sharp braking, most of which has been caused by following too closely.

The top five causes:

1. Tailgaters: The number one cause of phantom traffic jams is indeed motorists themselves who tailgate. If a vehicle is driving too close to the vehicle in front and the lead vehicle slows down then the following vehicle will have to brake sharply. So the easiest way to prevent phantom traffic jams is to keep a good distance from the car ahead. Emotionally, tailgating is infantile "bully" behavior to punish the driver ahead of you or make him go faster. But logically, keeping a safe distance behind will actually get you to your destination faster!

2. Slow bus: The number two cause is the slow bus. This can be any vehicle that pulls into the outside lane at a speed much slower than the general flow of traffic. It can be a bus or truck, but it is equally likely to be a car driver.

3. The cop: Yes, sometimes the police can trigger phantom jams. The lead car in the outside lane spots a police car on the hard shoulder or inside lane and brakes suddenly.

4. The "Your Speed" radar machine: The lead car spots the machine and brakes suddenly. The dominos begin to roll.

5. The rubbernecker: This problem occurs when there has been an accident on the opposite side and the rubberneckers brake hard to have a good look. This causes massive tailbacks and even when the accident is cleared away delays can still occur and hence the phantom traffic jam.

You cannot change other people's idiotic, dangerous behavior -- but you can change your own behavior. Keep two to three seconds behind the guy in front of you, if people pass and cut in front of you, take it in stride and drop back to a safe distance, and above all, stay alert. You are driving a killing machine.