Is speeding more dangerous than slowing?

Most of us will drive a car regularly and thus you will encounter fellow-motorists on the road. As I live about 100 km (~60 miles) from Davis, I have to commute to get to Davis. If only the train was affordable and reliable, I would use it, but it isn’t. So I drive my relatively fuel-efficient Hyundai Elantra to-and-fro Davis. This means I encounter 100s of fellow-motorists on a daily basis. As I didn’t grow up with California traffic, but with Dutch, German and Belgian traffic (ergo European road rules), I find myself both surprised and annoyed at the frequent and often pointless lane changes that my fellow-motorists make. Probably because my mind still tells me to stay right, unless I try to pass someone.
And I also did come by the CHP (California Highway Patrol) officer at one point. I was speeding, he told me. So he gave me a ticket for that.
This raises a question: is speeding really more dangerous then slowing (driver slower then the speed limit)?
The general consensus is that it is. Speeding is not only breaking the law, but also can cause serious harm. This is all true, but this does not mean that everyone who speeds is dangerous. In most cases it is the relative speed between you can your fellow-motorists that can make speeding dangerous. But rather then using logical reasoning alone, let’s use some simple math.

Let say the speed limit is 100 kmh (~62 mph). To travel 100 km, it would take you 60m00s.
If you would ‘speed’ by 10%, you would be going at 110 kmh (~68 mph) and you would need about 54m32s to travel the same distance, a gain of 5m28s.
If you would ‘slow‘ by 10%, you would be going at 90 kmh (~56 mph) and you would need about 66m40s to travel the same 100 km, a loss of 6m40s.
So time-wise, slowing has a more profound effect on time, then speeding. Often, the argument is made that because the time gain while speeding is limited, it is not worth it. Sporadically, if ever, the opposite argument is made.
But there is more to it then just time gain or loss, compared to the posted speed limit.

What effect does speeding have on time to respond vs slowing? How quick can someone who speeds respond to a situation, compared to someone who slows? In other words, can a car that slows speed up as quick as a car that speeds can slow down to the posted speed limit? Accelerating from 0 kmh to 100 kmh takes easily up to 10 seconds, whereas breaking from 100 kmh to 0 kmh requires about 120 meters or so. 10 seconds in a car covers more then 120 meters, so it would be fair to assume that slowing down takes less time then speeding up for the average driver.

Of course there is a lot more involved in driving a car, then just simply speeding or slowing or obeying the law (but who really does that on the road?). You rarely drive alone on the road, which means that you will encounter other vehicles who have to respond to what you are doing. Now let’s take the consequences of speeding and slowing on the odds of having to deal with a fellow motorist. For this let’s assume that everyone else is driving at the speed limit of 100 kmh. Slowing cars will encounter more fellow motorists then speeding cars. Now comes the crux. The slowing car has to either speed up to the average speed of 100 kmh or the fellow motorists have to pass the slowing car. The speeding car will encounter fewer fellow motorist, and has to either pass the fellow motorists or slow down to the average speed. If both the speeding car and the slowing car don’t change their driving style, the slowing car will force fellow motorists to change behaviour to more people than the speeding car .

Here in California, CalTrans has made multilane highways and it is not uncommon to find 3 or 4 lane highways per driving direction. As in the USA people drive on the right, the natural tendency is to pass another motorist on the left. This means that slowing cars are presumed to stay in the right lane, whereas speeding cars tend to stay in the left lane. Now imagine that a slowing car moves 1 lane to the left. It will encounter even more fellow motorists and thus force more motorists to change driving behaviour. Often this result in fellow motorists slowing down for slowing cars, as the left lane is often already filled with other motorists. How do we know this is a realistic prediction. Look at the highways now and see what happens when a big-rig moves one lane over to pass a fellow big-rig. Yep, traffic will slow down.

So you might say: California has a law that says that slower traffic must stay right. True. But when was the last time you saw a CHP officer pull someone over for slowing? Yep, they pull over people who are speeding. Easy money over guaranteeing flow of traffic or traffic safety.

Then comes psychology. How do people respond to slowing cars over speeding cars. Well, if you are stuck behind a guy who thinks that the left lane is his lane, while going 70 kmh, you will get frustrated. Besides being under the influence of a restricted substance or mobile device or sleep deprivation, frustration is not very helpful in light of traffic safety. You are probably more likely to make an erratic move, while focussing on the slowing car in front of you. In other words, you are paying less attention to your fellow motorist. Not particularly safe if you ask me.
Are speeding cars more or less safe? Obviously, speeding cars who frequently change lanes and tail-gate are dangerous, but these drivers are most likely speeding more then 10%. But cars who drive above the speed limit in a limited manner are per se dangerous. They can lift the throttle and let the car role out to get back to the speed level of the car they are approaching.

The one group of drivers I have not mentioned: the speeding/slowing drivers. They combine the worst of two world for one of the most fundamental dangers on the road: unpredictability. This should be enforced by the police, but clearly they prefer to sit on the side of the road and just get a single moment event of a speeding car.

Maybe it would be worth fining people who drive a certain percentage above AND below the flow of traffic over a strict and set speed limit with a limited fluctuation of speed itself, unless you change lanes? This can be done by lane-specific speeds, with slower in the right lanes and faster in the left lanes. Is this tougher to enforce? Yes, but what is more important: traffic safety or being able to use the public for gathering enforcement ‘tax’? Too bad we are currently in an economic recession, so we can only expect more speed-traps by the CHP. Of course this is all in the name of traffic safety and improving traffic flow.

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