SD 186

When it comes to how much weight you can haul on how many axles legally, each North American state and province has different bridge laws. In places like South Dakota and Michigan, trailer combinations may have upwards of 20 axles on them! They’re quite a sight to see cruising down the road. In other jurisdictions, axle numbers and weights are more restricted. A customer intending to operate exclusively in Michigan could take advantage of the higher axle and weight limits, while a customer crossing state lines won’t necessarily be able to utilize the same combinations.

Using Bridge Law Drawings

To help illustrate what can haul where, tools called bridge law drawings quickly depict specific truck and trailer combinations that can be legally used in each jurisdiction. Bridge law drawings show how much payload can be hauled and calculate the resulting axle loads from those payloads.

At SmithCo, we regularly create detailed bridge law drawings for customers’ reference. My goal is to help our customers maximize their payload hauling abilities while keeping the trailer weight and cost to a minimum--and to help ensure that any combination will be in compliance with regulations in all of the jurisdictions the trailer is going to be operating.

Finding the Best Trailer Combination

I start by asking our customers what type of truck they plan on pulling trailers with, the kind of payload they want to haul, the areas they will be hauling, as well as any other special information about their needs. Then, I research regulations for the states and provinces where the trailers will be hauled. From there, I am able to work up a combination that will meet regulations, maximize payload, and minimize cost. Sometimes this takes a few minutes, but for more complicated cases—like complex hauling through a variety of jurisdictions—it can take several days to design a bridge law drawing. In some cases, these drawings illustrate a turn radius layout to let our customers know how tight of a turn they can make with their truck and trailer combinations.

Beyond selecting the perfect trailer combination for the job, bridge law drawings are useful for our customers to verify the legality of a truck and trailer combination with their particular state officials long after they have selected their trailer. State DOT officials look for axle group dimensions and weights, overall trailer length, height and width of the trailer. The drawings make it easier to check all of the required boxes with each set of regulations.

Supporting our Customers

Some companies provide good quality drawings for potential customers and some will supply little more than a hand drawn sketch with basic information. At SmithCo, we take great pride in helping our customers select the best side dump for their needs and providing formal bridge law drawings is just one of the ways we consistently do that.

Want to know more about how SmithCo can help you get the most versatile trailer available? Get in touch, and we can start learning about your specific needs. Give us a call at 800-779-8099 or email us at

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