Do Trailers Need USDOT Numbers?

The short answer

The federal marking rule puts your name and USDOT number on both sides of the power unit: the truck or tractor doing the pulling (49 CFR 390.21T). That's where the requirement sits, on the truck, not the trailer. Beyond that, trailer lettering is mostly a fleet decision. One flag: the same federal section also covers intermodal equipment. If you run intermodal chassis, check the FMCSA rule for your equipment.

New York spells it out for in-state carriers: the name and USDOT number go on both sides of the power unit, never the trailer (NYSDOT, see our New York page).

The trailer still counts toward the weight

This is the part people miss. The federal test for a commercial motor vehicle is 10,001 lbs or more by weight rating or combination weight rating, or by actual weight, whichever is greater (49 CFR 390.5T). The trailer is on the truck's tab.

Say your pickup weighs 7,000 lbs loaded and you hitch a trailer and equipment that weigh another 5,000. On the scale that's a 12,000-lb combination. Cross a state line for work like that and name + USDOT go on both sides of the pickup, even though the pickup alone is under the line. Our hotshot guide walks through the same trap with bigger trailers.

States count combinations too, from our verified data:

• Pennsylvania: in-state trucks mark at 17,001 lbs, single or combination, so a pickup pulling a heavy trailer can cross it (67 Pa. Code 231.8, see Pennsylvania)
• South Carolina: 10,001 lbs, and a pickup that only crosses the line when towing may use magnetic signs while the trailer is hooked up (SCDMV intrastate DOT FAQ, see South Carolina)
• Illinois: 10,001 lbs, rating or actual, single or combination (625 ILCS 5/18b-101)
• Connecticut: 18,001 lbs, counting combination rating and weight (Conn. Gen. Stat. 14-163c)

Not sure what your combination is rated for? Our GVWR explainer covers GVWR, GVW and GCWR.

What goes on a trailer, by choice

Nothing below is a federal marking requirement. It's how working fleets keep track of equipment and get seen.

• Unit numbers. Dispatch, the yard and the shop all need to call a trailer by number. Put it on both sides near the front, plus the rear so it reads when the trailer is backed into a dock. Our unit numbers come matched in size and font across a whole range.
• A numbering plan. Give trailers their own block, such as 200s, so the number tells you what it is. See our fleet numbering system.
• Company name and phone. The front corner of a trailer side is the standard spot for name and unit number. A full side is the biggest sign you'll own.
• USDOT on the trailer. Add it if a customer or contract asks. It doesn't replace the marking on the truck.

Other trailer rules are separate

Trailers can have their own equipment, registration and hazmat requirements. Those aren't part of the marking rule and aren't in our verified data, so we don't summarize them here. Check with your state agency or the FMCSA (1-800-832-5660) for your trailer type.

Lettering a trailer that lasts

• Pick a flat panel. Keep letters off rivet rows, seams and corrugations. If a line has to cross rivets, plan it on the proof so the rivets fall between letters.
• Go bigger. Trailer lines are read from farther away. Our trailer package cuts every line at 3 inches.
• Prep the surface. Wash, then wipe with rubbing alcohol to cut road film and wax. Apply between about 50 and 90 degrees F.
• Big runs take two people. Anything wider than your arms should be hinged with masking tape and laid down from the middle.

We cut premium outdoor vinyl rated 5+ years. Every order gets a free digital proof first, free U.S. shipping, and ships 1-2 business days after you approve it (3-5 for 30+ sets with multi-color logos).

Decals for this

• Trailer Decal Package, from $54.95: name, unit number and weight lines cut to match, 3-inch lines
• Unit Truck Numbers, from $12.95: matched numbers for every truck and trailer in a range
• Box Truck & Trailer Lettering, from $89.95: your name across the full trailer side