How Overweight Loads Work

Logging trucks are likely candidates for overweight permits.
Freezing Rain | ©istock photo

We've all been there -- stuck behind a tractor trailer with what looks to be the world's largest grain silo resting heavily on the truck's 18 wheels. The driver sits staring at the suspension bridge just ahead, rifling through papers to try to determine if he can haul this heavy load across the span without collapsing it. Will he end up on the evening news or even worse -- YouTube? His reputation as a trucker is at stake and he instantly regrets his decision to veer from his pre-planned route to save a few hours. The bridge creaks and groans as the overweight load inches over the bridge -- crisis averted.

This scenario shouldn't happen. Chances are this imaginary trucker was operating outside the legal limits of where he could tow his overweight load. If he had the proper permits, he would know the regulations and restrictions for the route he'd planned. More than 500,000 overweight trucks are permitted each year in the United States [source: USA Today]. These permits range in price from $12 to $1,000, depending on the weight of your payload. If you plan on hiring a company for towing an overweight load, they'll get all the permits and details. It's what they're paid to do, so you don't have to worry about it. Unless you're moving your home though, you'll probably never be faced with an oversized load dilemma -- most of these loads come from commercial shippers.


­Each state and each city within each state has specific rules for what constitutes an overweight load and when and where you can haul one within its boundaries. For instance, in Wisconsin an overweight load is when the maximum gross weight of the vehicle and its load exceeds 80,000 pounds (36,287 kilograms). Most interstate highways have the same 40 ton regulation. However, some states allow exceptions to that limit because of influence by lobbies from local industry. Texas allows the limit to be exceeded by as much as two tons and Nevada has permitted one-time exceptions up to 170,000 pounds (77,110 kilograms) [source: USA Today].



How to Tow an Overweight Load

Six of 18
Each of these two wheels is connected to two others on the opposite side by an axle.
marekp | ©istock photo

State and local governments regulate overweight loads for one reason -- to preserve their infrastructures. Repeatedly driving overweight loads on highways, local roads and bridges wears them down over time, resulting in ruts, cracks and potholes. A government study found that a single overweight truck carrying the maximum 80,000-pound (36,287-kilogram) load does as much damage to a highway as 9,600 cars do[source: USA Today].

One of the big problems with heavy loads is that extra weight has an exponential effect on the road's surface. Let's say you have two trucks, each with an overweight load. One comes in at the legal limit of 20,000 pounds (9,071 kilograms) and the other at double that amount -- 40,000 pounds (18,143 kilograms). Instead of doing twice as much damage, the overweight load actually comes in at 16 times more damage.


If you're planning on towing an overweight load, here are some things to consider: Loads are typically broken down into two groups -- axle load and tire load. The axle is the central, rotating metal shaft that connects the wheels opposite each other. Axle load refers to the total weight spread out over the entire vehicle. Tire load references the narrow concentration of weight from the load sitting on each tire. Axle weight isn't affected by the width of a tire, so 20,000 pounds (9,071 kilograms) sitting on a 12-inch (30-centimeter) wide tire puts the same stress on a road or bridge as that same weight on narrow, 6-inch (15.24-centimeter) tires. Permitting is typically broken down into categories depending on how many axles and tires you have compared to how much weight you're hauling.

Towing overweight loads requires some experience in order to make it safe journey. Stopping distance and how your car or truck handles are the two main issues at play. Auto brakes respond differently when there's extra weight involved -- the same goes for steering. You'll want to give yourself extra space between you and the car in front of you and anticipate your stops well in advance. Sudden swerving is difficult to control with an overweight load as well, so the straighter and less congested your route, the better.

Now that you know a bit about how to tow an overweight load, head to the next page for some more tips on the process.



Overweight Load Towing Tips

Overweight load towing causes bridge damage. Bridges show signs of wear and tear in the form of fatigue cracks in the structural steel and cracks in the concrete members that hold the bridge up. If state authorities deem a bridge stressed or fatigued, they can list the bridge as "load restricted," meaning that no overweight loads can cross it. If the problem gets even worse, they may classify it as "load posted." This means lowering and posting a new weight load limit for all vehicles. If things get past that point, the bridge may be closed altogether for repairs or even permanently.

Some investigators say that stress from overweight loads may have helped contribute to the bridge collapse in Minneapolis, Minn., in August 2007. Thirteen people died in that accident. In 2000, a bridge in Wisconsin that supports frequent overweight loads collapsed. A federal study found that 18 percent of bridge weight limits are either not posted or are incorrect. The same study found 26 percent of our bridges structurally deficient [source: USA Today].


What overweight load towing considerations should you keep in mind as you traverse roads and bridges? Stress cracks and weight damage can happen on concrete and asphalt -- that's why the specific route is required for submission when permitting and overweight load. So, it's important if you get permitted for a specific route to not deviate from it.

The worst accidents you see on the roads are when an overweight load truck has turned over. Not only is it dangerous because the size of the truck, but there's also a heavy payload now scattered across the highway. A logging truck carrying two dozen full-size trees crashing on a busy highway is way more dangerous to other drivers than a contained, normal-sized load. Overweight loads also make it more difficult to regain control in case of an emergency maneuver. Having the weight evenly distributed on the truck bed is vital to the steering performance, so packing the load is something that's planned out with great caution.

If you're driving on the road in your car, give overweight loads plenty of room to operate and avoid driving in their blind spot. If you pass, do so quickly and give yourself plenty of room to avoid cutting them off after the pass is complete. You shouldn't follow too closely either -- anything within three to four car lengths behind the truck can't be seen by the truck driver.

For more information on overweight loads and other towing challenges, please visit the links on the next page.


Lots More Information

Related HowStuffWorks Articles

More Great Links


  • "Determine if a permit is required." Wisconsin Department of Transportation. 2008.
  • "Legal Load Limits, Overweight Loads and Pavements and Bridges." 2008.
  • "Oversize Loads - Routing High and Wide." 2008.
  • "Oversize Loads." 2008.
  • Castro, April. "Overweight trucks punish roads, bridges with states' permission." USA Today. Sept. 10, 2007. ­