While the term semi trailer is used by the public to refer to the common box trailer-tractor cab combinations seen driving down the highway, the reality is that this word encompasses a vast array of trailer types. For those who work in the industry, understanding the specifics of semi trailer dimensions and what each style of trailer can haul is key.
The following guide will walk through common trailer styles, their dimensions, including length, width, and height, as well as what capacity loads they can haul. Additionally, a few key regulations around semi trailer dimensions and load weights will be outlined, helping operators understand when specialized permits are required by state.
Not all semi trailers are designed with the same use case in mind. For this reason, their dimensions and load weight vary based on what they are intended to haul. The following list curated from Paige Ltd. quickly breaks down some of the most common semi trailer dimensions.
Flatbed trailers can haul a maximum weight of 48,000 pounds. However, tri-axle trailers can haul up to 65,000 pounds, making them ideal for heavy cargo.
Common dimensions for flatbeds are as follows:
Dry vans boast a freight weight of 42,000 pounds to 45,000 pounds, depending on the specific van. A dry van with a tri-axle, however, can haul up to 63,000 pounds.
Common dry van dimensions are as follows:
Refrigerated trailers are designed to transport temperature-sensitive items, such as produce, dairy goods, and other foods. Their max freight weight is 42,000 to 45,000 pounds for a standard refrigerated trailer and 63,000 pounds for a tri-axle.
Common refrigerated trailer dimensions are as follows:
Lowboys offer a maximum cargo weight of 40,000 pounds for a standard two-axle trailer. You can add on an additional trailer and cargo combination weight of up to 95,000 pounds depending on the number of axles used.
Common lowboy trailer dimensions are as follows:
Step decks are designed with a maximum freight weight of 48,000 pounds for a standard trailer. A tri-axle offers a freight weight of 65,000 pounds.
Common step deck trailer dimensions are as follows:
When operating a semi trailer, it’s not just about how the trailer itself was designed to carry loads or how large a manufacturer can create the trailer to be. More importantly, it is also about following the legal regulations surrounding trailers. According to the U.S. Department of Transportation Federal Highway Administration, the following are the mandated maximum weights for the National System of Interstate and Defense Highways:
80,000 pounds gross vehicle weight
20,000 pounds single axle weight
34,000 pounds tandem axle weight
Interestingly, a key consideration for semi operators is the spacing of axles. The Federal Highway Administration looks to protect bridges by calculating the number and spacing of axles carrying the load weight. This is called a bridge formula and is applied to commercial vehicles to ensure compliance.
The specific formula from the Federal Highway Administration is as follows:
W=500(LN/N-1 + 12N + 36); where W=overall gross weight on any group of 2 or more consecutive axles to the nearest 500 pounds. L=distance in feet between the extreme of any group of 2 or more consecutive axles, and N=number of axles in the group under consideration
When it comes to hauling oversize loads, the federal government is not the one to issue permits to operators. Instead, this is handled on a state-by-state basis.
When hauling cargo across state lines, it is critical to understand what semi trailer dimensions are allowed and what requires additional permitting.
Different states have their own regulations for oversize load permitting, which can make the matter even more complex. The following information gathered from Coast to Coast Trucking Permits extensive state-by-state list helps to highlight the exceptions of which trailer operators should be aware.
The majority of states allow you to haul 20,000 pounds on a single axle trailer without a permit. However, this is not the case for every state. The following list breaks down states that do not adhere to this regulation, including information about what necessitates permitting. (Note: in some cases, state’s will allow for heavier loads than the standard):
When it comes to hauling heavy cargo, gross weight is an important consideration beyond just cargo weight. The majority of states follow the regulation of 80,000 pounds gross weight. However, certain states have different allowances as outlined below (Note: in some cases, states will allow for heavier gross weight allowances than the standard):
In general, states abide by the width restriction of 8 feet 6 inches. However, in some states there are exceptions based on the road or load type:
The majority of states allow for a standard height of 13 feet and 6 inches before necessitating special permitting. The following are states that operate with different regulations:
When it comes to choosing a semi trailer, the right dimensions and load capabilities are critical to getting the job at hand done. Whether you are hauling goods around town or across the country, at Transwest, we are here to help you acquire the trailers you need to get the job done. Talk to our knowledgeable staff today about purchasing additional trailers for your fleet.
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