Why Do Semi-trucks Drive Slower Than Everyone Else?

By RPRitter


Once again, I'm stuck behind a slow-moving semi-truck throwing up lots of rain, dirt, and rocks and taking his sweet time getting down the road. Like everyone else, I drive down the freeway pretty regularly and it seems like I spend a lot of my driving time avoiding semi-trucks. Why is that? Can't the drivers go any faster and stay up with traffic? I did some research and here's what I found.

David Versus Goliath

As I'm driving I see a weight placard that said the trailer weighed 4o tons. I did the math in my head and came up with 80,000 pounds of total weight. And that was just for the trailer and its contents! The truck pulling the trailer wasn't any lightweight and when I pulled alongside the tractor as I passed, I saw a sticker that said it weighed almost 16,000 pounds all by itself! Man, oh, man, that's almost 100,000 pounds of vehicle traveling down the highway at 70 miles an hour!

Feeling a little exposed in my SUV, I thought about how much it weighed compared to the behemoth rolling a few feet away. If my car weighed more than 6,000 pounds I'd eat my hat and that means I've got 3 tons of metal going up against 30 times as much vehicle. I felt extremely small and insignificant by comparison and I was right! And David thought Goliath was a substantial opponent!

Physics Are in Control

You might think the driver behind the wheel of the tractor pulling the trailer(s) has complete control of the entire package but the fact is that they don't have 100% control. Physics plays a big part in truck driving and when you've got around 50 tons traveling forward at 70 miles per hour you've got the equivalent of a diesel train engine rolling over the pavement. What that means is semi-trucks DO NOT stop on a dime or turn on a nickel, it's just not physically possible. That's part of the reason semi-trucks go slower than everyone else, I found out. Because truck drivers understand how much time, distance, and brake force is required to bring their rig to a stop and because most car drivers are clueless about this reality, truck drivers have to go slower if only to avoid accidents with all the cars buzzing around like fireflies on a summer evening.

A Little Education Goes a Long Way

Wanting to understand more, and needing a bathroom break, I pulled into a truck stop along the side of the highway and went inside, determined to get a cup of coffee and an education. I stepped up to the counter and sat down next to what I assumed was a veteran driver. His clothing, hat, demeanor, and solitude told me he was probably the best candidate to become my mentor. I sat down, he grunted, and I asked if he was driving one of the rigs parked outside. He grunted again and nodded his head so I launched into my 20 questions. Luckily for me, the driver was nice enough to answer every question I asked, as long as I kept his coffee mug filled. What I learned was amazing!

Hitting The Highlights

We talked for quite a while, given that the driver made three trips to the restroom during our discussion. Without getting into too much detail I found the answers to my question about why truck drivers always go slower than the traffic around them, and the main points were:

Machinery - Some trucks go faster than others and some trucks have devices that limit how fast they can go. The limit is set and can not be exceeded no matter how much the driver wants to go faster. In addition, it also takes more time for a semi-truck to get up to road speed. Sometimes drivers have to shift through 13 or 15 gears to get to freeway speed. That takes time and there's nothing a truck driver can do about it.

Monitoring - With all the GPS technology everywhere, trucks can be tracked by satellite and the speed of the truck can be determined quickly and accurately. That means the trucking company can tell if a driver is exceeding speed limits or company policies without the driver ever knowing.

Mistrust - Truck drivers with any experience have learned not to trust car drivers - ever. Most car drivers think trucks can stop, turn, and brake like they can and as a result, car drivers do some pretty dumb maneuvers around trucks. Veteran semi drivers know it's better to go slower because of the danger car drivers pose everywhere they go.

Mountains - Going up a long, steep hill is going to cause a semi-truck to slow down due to gravity, weight, and power. Going down the hill is the dangerous part. The truck has to start down the hill as slowly as possible because physics will eventually take over and force the truck to go faster and faster down the grade. Smart, experienced truck drivers know they may be impeding traffic but they're doing what they have to in order to stay in control of the 50 tons of destruction they're sitting in front of.

Money - Driving faster requires more fuel because the engine is running at higher RPMs. Fuel costs money and saving money means making a profit. Trucking companies are pretty keen on making a profit and staying in business so they tell the drivers to run the trucks at lower RPMs and that means slower road speeds.Multi-speed Limit Freeways - Many states require semi-trucks to maintain a slower speed than automobile traffic on their freeways and highways. Truckers are forced to be a traffic impediment by law and not by choice.

Good News and Bad News

I guess I can only sum up my investigation as a Good News/Bad News kind of situation. The good news is that I now understand why semi-trucks drive slower than the rest of the population. There are actually lots of reasons they do it and the reasons all come down to common sense and science. The bad news is that it isn't going to change much in the near future. I'm still going to be driving around semi-trucks every time I drive down the highway. At least now, I know why.