BOSTON -- When you're driving, you observe the overall flow of traffic.

Traffic moves in a fluid manner, not dissimilar from the movement of a river or stream. Not everyone is moving at the same pace, but there's a general flow that is predictable and observable.

When a vehicle enters this flow by bouncing from lane to lane and changing speeds, it interrupts the flow. It creates an unpredictable commotion. It's in this commotion, this disruption, that there is a higher risk of collisions and injury.

Predictability may not be something you ascribe to in daily life. It's not considered romantic to be predictable, but it's a very important in being a good driver.

You've seen the driver who is all over the road, weaving between lanes, tailgating, and speeding up or slowing down. He's always looking for the fastest lane, impatient to get there, wherever that may be, as fast as possible.

This kind of driving behavior causes crashes. When someone is driving unpredictably at varying speeds and quickly changing lanes in an unsafe manner, it makes it much more likely that other people will make a wrong decision.

It's also much more likely that other drivers will be unaware of his presence. Often this kind of erratic behavior will result in a collision that doesn’t even involve the driver who was acting erratically.

The ironic thing is that this erratic driver likely thinks he's a good driver. That's why he’s driving like he is.

It's this unfounded confidence in his own ability that convinces him that he can drive in a far riskier manner without consequence. It disregards the needs of other drivers for predictable and consistent behavior on the part of other drivers. It's this false skill that puts the rest of us in danger.

We have no way of knowing where he is going next, if we even know he's there in the first place. This unpredictability is a major issue in collisions.

The truth is the actual amount of time saved by a driver weaving in an out of traffic is quite small. Admittedly, it is a little faster, but only a little. Let's list the downside:

Increased likelihood of crash

Rude

Wastes gas -- excessive accelerating and decelerating burns much more fuel.

Increases stress

Increases road rage

Increased wear and tear on vehicle

In the event of a crash:

Cost of repair

Lost time of due to repair

Potential injury

Lost time due to injury

Cost of injury treatment

Increased auto insurance rates for everyone

The fact is that the more chances you take on the road, the more you change lanes, weaving in and out of traffic, the greater likelihood that you will make a bad choice. Even if you have better reaction time and better reflexes than the rest of us, the fact that you are driving in such a risky manner means that you are more likely to be involved in or cause a crash.