Have you ever seen a long line of trucks pulling off the interstate and wondered what was going on? Either they’re heading into a weigh station, or there’s a car load of spring break bound college girls that have a flat tire. Either way, it’s the law to stop…isn’t it?

Weigh stations are set up by the DOT (Department of Transportation) and are usually manned by state troopers and/or vehicle enforcement officials. Their main purpose is to check vehicle weights, but they also do vehicle and driver inspections when the mood strikes them, which usually just so happens to be when you’re behind schedule on a tight load.

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Weight limits in the U.S. are limited to 12,000 pounds on the steer axle, 34,000 pounds on the drive axles, and 34,000 on the trailer, or tandem axles. Add them together and you get a gross maximum weight of 80,000 pounds, or 40 tons. If the trailer has single axles instead of duals, 20,000 pounds is usually the limit for each axle. Special permits can be purchased for oversize loads.

The weight of the vehicle itself determines how much freight you can haul. The typical company-owned truck/trailer combo that you see usually weighs in the 34-35,000 pound range, which leaves enough room for 45-46,000 pounds of freight. The trick is getting all that weight distributed well enough to avoid an overweight ticket. Truckers call this “axling out.”

Bridge laws determine how you need to distribute your weight. (For a detailed explanation and a cute little visual of the bridge law, click here.) In short, bridge laws determine how far your drive axles (on the truck) must be from the trailer axles to avoid damaging bridges. These laws vary from state to state, so you need to find out which states you will be traveling through and then adjust your tandems to meet the minimum requirements for your trip. At 40 feet from kingpin (the knob on the trailer that hooks to the tractor) to the center of the rear most axle, California is the shortest distance. If you’re going to axle out a heavy load going into California you must get most of the weight between your axles.

There are three basic ways to get your load to axle out.

  1. Load the freight evenly – Most trailers nowadays are 53 feet long, but the weight of your freight determines how much of the 53 feet you can use. If you’re hauling styrofoam coolers, you can load it from floor to ceiling, all the way to the trailer doors. However, if you’re loading only nine-5,000 pound coils of metal, you’d better space those suckers out to avoid being over the 34,000 pound axle limit. Learning how to position freight comes with experience, but in general, if you can get a 45-46,000 pound load within the first 48 feet of trailer space, you can get it to axle out. Why do you need to leave 5 feet at the rear of the trailer empty? That’s where bridge laws and our next method come into play.
  2. Slide your tandems – Before you go on, why don’t you go on over to the Free Stuff page and download the free PDF describing the axling process. It will make these last two steps easier to understand. Most trailers are built on a rail system that enables you to slide the trailer box independently from the frame. This is done by pulling a lever near the trailer’s axles or operating an air-powered switch inside the cab, which in turn pulls 4 pins out of a sliding rail underneath the trailer box. You then lock your trailer brakes, release your tractor brakes, and start sliding your trailer along the rail system.When you get it where you think you want it, you release the lever under the trailer, jump back in the truck and slide the trailer a few more inches until it locks in place.
  3. Slide your fifth wheel – This is the part of your tractor that hooks onto the trailer’s kingpin. On some trucks the fifth wheel is adjustable for fine tuning an extremely heavy load. I’d rather be forced to watch reruns of General Hospital for days on end than slide a fifth wheel. They aren’t used nearly as often as the trailer sliding system and therefore are typically as cranky as the old lady down the street who smells like cat urine and mothballs. If you must do so, you slide the fifth wheel much like you would the trailer, however, you start by lowering the trailer’s landing gear to the ground. This is usually necessary to take most of the weight off the stubborn little fifth wheel. You then lock the trailer brakes, release the fifth wheel pin (either manually or air-powered), and start sliding the fifth wheel by moving the tractor forward or backward. Brace yourself before you start moving because when and if it ever unlocks itself, it will usually jar you hard enough to cause you to vomit up your spleen.

So there you have it. But how do you know if you need to adjust your weight in the first place?  Well, again, that mostly comes from experience. I feel pretty comfortable guessing where the tandems should be on loads under 40,000 pounds. However, if something looks fishy to my experienced eye or a load is heavier, I simply slide them to where I think they need to be and head for the nearest truck stop with scales, which is most of the major truck stop chains. The first weigh will run you $8 to $10 (price goes up periodically). If you’re over the 80,000 pound limit, you’re probably going to be heading back to the shipper for reloading. If you’re just overweight on one set of axles, you can pull off the scale, slide your tandems a bit, and reweigh for $1, as long as the reweigh is within 24 hours and it takes place at the same truck stop where you did your first weigh. If you can’t get legal on all three axles, you’re most likely headed back to get your load adjusted by the shipper. By the way, the majority of carriers reimburse the cost of scales. If not, save them for tax time.

Although you can get most loads to axle out with room to spare, every once in a while you’ll encounter a load where the best you can do is 100 or 200 pounds overweight, either gross weight or on a particular axle. Before I head back to the shipper, I ALWAYS call my company first. I’ve had numerous occasions where they told me to run with the load because some particular weigh station you’ll be crossing will allow a little leeway. Don’t ever try this without permission and always get permission in writing (via satellite). If they won’t give it to you in writing, refuse to haul it. Overweight tickets are notoriously expensive, and it will be yours to pay if you can’t prove you were told to run with it.

Weigh stations are a pain-in-the-wazoo, but unfortunately, they are a necessary pain-in-the-wazoo. Luckily, some companies provide a wonderful little savior that sticks to your windshield. It’s called a PrePass. Just as a toll pass allows you to roll past toll plazas, PrePass allows you to pass weigh stations. At least most of the time.  And that’s why I say, “Please, oh please, give me the bypass!”

About the Author
I'm a 22-year truck driver with an interest in tech stuff. I do the Trucker Dump podcast and blog, which is all about life as a trucker. I have also written two trucking books, "Trucking Life" and "How to Find a Great Truck Driving Job."
8 comments on “TD28: Please, Oh Please, Give Me The Bypass!
  1. Truck Drivers News says:


    Great post! This is something I have not had to deal with, and when I did have to deal with it, never really understood it. I pulled dumps, tanlers, and flat bed, never had sliding tandems to have to mess with.

    This post explains it, and makes it sound so simple! Keep it up!

    1. Todd McCann says:

      Glad I could keep it simple enough to understand. Quite frankly, I don’t have the brains to get all technical on everyone. I just call ’em as I see ’em.

  2. Tretter@yahoo.com says:

    umm… I am no

    1. Todd McCann says:

      I am no… what? Now I’m the one that is confused. 🙂

  3. Rejser til Finland says:

    OP: I could be daff (lord knows I have been told lol) but you made totally no sense…

    1. Todd McCann says:

      That happens a lot. Sorry if I confused you. It’s not that hard to understand when you can see first-hand how this works.

  4. Christy Kuppler says:

    I thought that this was very well written and very informative. The one thing that I always get confused on is which way to slide my tandems.
    Do I slide them forward, (toward the trouble) or back further if I’m heavy on the drive axles?

    1. Todd McCann says:

      Thanks for the comment and question, Christy.

      First, download the free PDF I mentioned in the article. Then follow along.

      If you’re heavy on your drive tires, you’d want to slide your trailer tires forward (towards the tractor). Think of this way.

      Forget the tractor and the drive axles for a bit. I look at the trailer like a giant seesaw, where the trailer tandems are the pivot point. If the trailer tires could be in the middle, the weight on both ends would be the same (if the load was equally balanced). Move the trailer tires all the way to one side, and all the weight shifts to the other side.

      Now for a real example. What would happen if the trailer tires were slid all the way to the rear? That’s right. All the weight would shift to the nose, putting more weight on the drive tires.

      I tried to think of a catchy phase that would help. Assuming your looking at it from the driver’s side, here’s the best I could muster:

      Trailer tandems light? Move the load right.

      Hope that helps.

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