New Mexico Semitrailer Length Limit

New Mexico is grandfathered at 57'6". Every state must allow 48 feet on the National Network; New Mexico kept the right to allow 57'6" and cannot drop below it.

Appendix B length57'6"

Federal floor48'0" (all states)

Kingpin conditionNone

Tractor + 2 units86.4K(3)

Tractor + 3 unitsNot allowed

This is a floor, not your length limit. Appendix B lists what a state was grandfathered to keep under the STAA of 1982 and must go on allowing on the National Network. It is not the state's own limit, and it is not permission to run that length on any road you like. Most states allow 53-foot semitrailers under their own law — that permission comes from state statute, not from this table — and every state can still restrict length on specific routes, in cities, and off the National Network. Use this to know the federal baseline, then check the state limit and the route.

01 The rule

What New Mexico has to allow

New Mexico kept 57'6" under the STAA grandfather, so anything up to that length is federally protected on the National Network and New Mexico cannot legislate below it. A standard 53-foot van sits comfortably inside it.

The number comes from 23 CFR Part 658 Appendix B, the STAA grandfather list. It binds New Mexico on the National Network and cannot be lowered. It says nothing about what New Mexico allows beyond it, which is where state law takes over.

02 The details

Length, kingpin and combinations

Appendix B semitrailer length: 57'6"
Kingpin-to-rear-axle condition: None in Appendix B for this state.
Tractor plus two trailing units: 86.4K(3)
Tractor plus three trailing units: not allowed
Other grandfathered combinations: not allowed
Past the legal length: a New Mexico oversize permit — see New Mexico oversize permits.

New Mexico Trailer Length FAQ

What is the legal trailer length in New Mexico without a permit?

The federally protected length on the National Network is 57'6" (23 CFR 658 Appendix B). New Mexico was grandfathered above the 48-foot floor and must keep allowing it.

Can I run a 53-foot trailer in New Mexico?

Yes. New Mexico is grandfathered at 57'6", so 53 feet is inside the federally protected length on the National Network.

Are doubles or triples allowed in New Mexico?

New Mexico holds grandfathered longer-combination-vehicle rights under Appendix C. Tractor plus two trailing units: 86.4K(3). Tractor plus three: not allowed.

Does this length apply on every road in New Mexico?

No. Appendix B binds the National Network — the Interstates plus the designated primary routes. Off the network, and inside cities, New Mexico can and does restrict length, and posted route restrictions still apply. Check the route as well as the number.

Reference information for planning, not legal advice. Traffic laws change and this can be out of date, so always confirm the current statute and obey posted signs before you rely on it. Last reviewed July 2026. Source: eCFR, 23 CFR 658 Appendix B and C (title 23 as of 2026-07-23). See our Terms & Disclaimer.

03 Related

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New Mexico Semitrailer Length Limit

What New Mexico has to allow

Length, kingpin and combinations

New Mexico Trailer Length FAQ

More for New Mexico

New Mexico Weight Limits

New Mexico Oversize Permits

New Mexico 511

All States

Check New Mexico before you roll