---
title: "semi-trailer: Definition and Meaning | NPSA"
description: "A semi-trailer is a trailer built so that part of its weight rests on the truck that pulls it."
url: https://npsa.preview.multisites.ai/glossary/semi-trailer
publisher: National Portable Storage Association (NPSA)
phone: "(816) 960-6552"
email: info@npsa.org
---

Industry and products

# semi-trailer

A semi-trailer is a trailer built so that part of its weight rests on the truck that pulls it. Federal motor carrier rules define a semitrailer as a motor vehicle, other than a pole trailer, that another motor vehicle draws and that bears partly on the towing vehicle.

## Why it matters

Most storage trailers are semi-trailers. A tractor pulls the trailer, and a front landing gear holds up the front end when the trailer is parked. This matters for operators because a trailer on the road is a regulated vehicle. Federal rules in 49 CFR Part 390 and related parts may apply, and states add their own rules for registration, inspection and lights. A common mistake is to think a parked trailer on a customer site is exempt from upkeep. Brakes, tires and lights still need attention before each move. Operators should also check what the tractor and driver need to be legal. Check state and local rules, and ask a compliance professional.

[Read: Storage trailers](https://npsa.preview.multisites.ai/storage-trailers)

Definition source: [law.cornell.edu](https://www.law.cornell.edu/cfr/text/49/390.5)

## Related terms

[### storage trailer A storage trailer is a trailer used as a movable storage space instead of for hauling cargo from place to place. It has a floor, walls, a roof and doors at one end or both. NPSA members rent, lease and sell storage trailers, often in standard lengths from 28 to 53 feet.](https://npsa.preview.multisites.ai/glossary/storage-trailer)[### tag trailer A tag trailer, or tag-along, is a trailer that hitches behind a truck on a drawbar or pintle hitch instead of a fifth wheel. Many tag trailers have decks that tilt so equipment can drive on without ramps. Capacity ranges widely, from light to heavy duty.](https://npsa.preview.multisites.ai/glossary/tag-trailer)[### chassis A chassis is a skeletal semi-trailer built to carry a container. It has twistlocks at the corners that lock into the container's corner castings. Chassis are used with tractors to move containers on roads between ports, rail yards and depots.](https://npsa.preview.multisites.ai/glossary/chassis)[### FMCSA FMCSA is the Federal Motor Carrier Safety Administration, an agency within the U.S. Department of Transportation. It writes and enforces safety rules for commercial motor vehicles and carriers, and it handles registration for interstate carriers. Its rules are in the Federal Motor Carrier Safety Regulations.](https://npsa.preview.multisites.ai/glossary/fmcsa)[### DOT number A DOT number is an identifier assigned to a company that operates commercial vehicles. Most people mean the USDOT number issued by FMCSA. It tracks a carrier's safety record from audits, inspections and crash reports. Rules differ by state for in-state carriers.](https://npsa.preview.multisites.ai/glossary/dot-number)[### GVWR GVWR is gross vehicle weight rating. It is the maximum loaded weight of a single motor vehicle, as set by the manufacturer. It includes the vehicle, fuel, driver, cargo and equipment. It is printed on the vehicle's certification label and set by the maker.](https://npsa.preview.multisites.ai/glossary/gvwr)

[All 220 terms](https://npsa.preview.multisites.ai/glossary)

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