The 18-Month Rule Has No Rules: Where It Came From and When to Break It

Put two carriers in front of me. Carrier A: MC issued 11 months ago. Carrier B: MC issued 22 months ago. Under the standard broker rule — no carriers with less than 18 months of authority — Carrier A goes in the decline pile and Carrier B gets a callback.

Now I'll tell you that Carrier A has 28 roadside inspections in those 11 months with a 3.5% OOS rate, and Carrier B has 8 inspections over 22 months with a 37.5% OOS rate. You'd book Carrier A without thinking twice and run hard from Carrier B. But the 18-month rule — applied strictly — told you the opposite.

That's not a quirk. That's the rule working exactly as designed, and still producing a bad answer.

Where the Rule Actually Came From

The 18-month rule is not in 49 CFR anywhere. It's not in a carrier safety circular. It's not even in most brokerage compliance manuals as anything other than a number that appeared, got passed around, and became orthodoxy.

What it's based on is real: FMCSA crash data consistently shows that carriers in their first 18 to 24 months of operation have elevated crash rates compared to the carrier population as a whole. New entrants are more dangerous on average. The rule is industry shorthand for that statistical pattern.

The shorthand isn't wrong. It's just being applied as a binary switch when it should be a question — do I have enough data to assess this carrier's safety performance? — and the answer to that question has more to do with inspection count than calendar months.

Under 49 CFR § 385.5, FMCSA determines a carrier's safety fitness by evaluating its safety management controls using data from inspections, crashes, and compliance reviews. The FMCSA's own methodology acknowledges what every broker who's thought hard about this already suspects: you can't make a meaningful safety fitness assessment from a thin record. Time alone doesn't create data. Inspections do.

Eighteen months is a proxy for "probably enough inspections to tell me something." For a carrier running dedicated lanes with predictable inspection exposure, 18 months might mean 30 cleanish inspections. For a carrier running short hauls in low-enforcement corridors, 18 months might mean 5 inspections — a sample size that tells you almost nothing.

When the Rule Is Right

When a carrier's MC is 6 months old, they have a thin safety record, and you don't know why — new authority is the right call. You're not being paranoid. You're acknowledging that there isn't enough information. That's a fair position.

It's especially right with larger fleets going out under fresh authority. A 10-truck operation that formed a new entity to haul under a new MC, with limited capital, new drivers, and no compliance history, is exactly the elevated-risk profile the 18-month rule was built to catch. They may be perfectly capable carriers. They may not. You don't know. You don't have to tender them $75,000 of freight to find out.

And in a post-Montgomery world, it's a defensible policy position. Montgomery v. Caribe Transport II, decided by the Supreme Court in May, killed the FAAAA preemption defense that used to insulate brokers from state negligent-selection claims. You can now be hauled into state court for putting an unsafe carrier on a load. A bright-line policy — we require at least 18 months of authority and at least X inspections — is the kind of written standard that holds up in discovery. If you don't have something written down, "we applied good judgment" is not a great answer under oath.

When the Rule Is Wrong

Here's where most brokers stop thinking.

The veteran owner-operator who just went independent. This is the most common scenario where the rule gives a bad answer. A driver runs under MC-1056428 for nine years. They've got a clean PSP report, no crashes, no violations, real experience. They get their own authority six months ago. Their MC is brand new. Their safety record is not.

Under 49 CFR Part 376, every carrier that leases an owner-operator must have a written agreement, and the FMCSA keeps that operational history in the PSP (Pre-Employment Screening Program) report. When you pull a PSP on a veteran OP who recently went independent, you're looking at years of roadside inspection history from when they operated under someone else's authority. That record doesn't disappear when they get their own MC.

If a driver has a PSP report showing 60 inspections over 9 years with 2 violations, both minor equipment — that's not a new entrant. That's a career professional who filed some paperwork six months ago. Applying the 18-month rule to them wholesale is a mistake.

The carrier with a dense inspection record in a short window. A carrier running regional truckload freight out of a high-inspection corridor — interstate 80 through the Midwest, I-35 through Texas — can accumulate 40 inspections in 10 months if they're running hard. At 40 inspections with a 5% OOS rate, you have a statistically meaningful picture of a carrier's safety performance. It's not perfect, but it's real data. You have more information about that carrier than you'd have about a quiet 22-month carrier with 8 inspections.

The right question isn't "how old is this MC?" It's "how much inspection exposure has this carrier had, and what does that history look like?"

The carrier that bought an established operation. This one is subtle. Sometimes a carrier's MC number is old but the operation behind it changed completely. Officers changed, drivers turned over, equipment sold off and replaced. The 18-month clock never restarted. But the entity you're booking bears little resemblance to the entity that built the inspection history in SAFER. This is the flip side of the same problem — the rule doesn't flag it because the calendar says the carrier is mature.

What Actually Replaces the Rule

The 18-month rule is really asking: is there enough inspection history to make a judgment? So check that directly.

First, look at the raw inspection count in the SAFER carrier snapshot. If a carrier has fewer than 10 inspections in SAFER, you don't have much to work with regardless of how old the MC is. If they have 30+, you have a sample that starts to mean something.

Second, look at inspection dates. If a carrier has 10 inspections, are they spread across 18 months or crammed into one week because they ran a dedicated contract that required daily DOT contact? Dense clusters can indicate unusual exposure, not sustained operations.

Third, look at the OOS rates — both driver OOS and vehicle OOS — against the carrier's inspection count. A high OOS rate on a thin inspection record might mean two bad weeks. A high OOS rate on 30 inspections is a pattern.

Fourth, for any carrier under 18 months with an experienced operator, pull a PSP report and ask them directly about their history before the MC was issued. "Were you hauling under someone else's authority?" is not an unreasonable question. If they were, there's a paper trail.

Fifth, if you're going to make an exception, monitor tighter. A carrier under 18 months on your approved list should be on Continuous Monitoring — meaning you're notified the moment their insurance status, safety rating, or authority changes. You didn't have the history to fully vet them; monitoring is how you compensate.

How I Document This

When I grant an exception to the 18-month rule, I document four things in the carrier file:

First: the reason for the exception. Not "seemed fine" — specifically: veteran operator with X years of PSP history on file, inspection count of N with OOS rate of Y, placed on enhanced monitoring.

Second: the PSP or inspection record that supported the exception, attached to the carrier file. If the carrier's prior history was the reason I booked them, I want that history in the file, not just my memory of reviewing it.

Third: the monitoring flag. In DOTScreener, I note in the record that this carrier is below our standard tenure threshold and should stay on Continuous Monitoring until they cross 18 months. The system re-files a Carrier Selection Record when material changes occur, which means if something does go wrong with this carrier in their early months, my file shows I was paying attention — I wasn't just hoping for the best.

Fourth: the load value and cargo type. If I'm making an exception for a newer carrier, I generally start them on lower-value loads. That's documented too: first load was $22K, 28k flatbed, no special handling requirements. That's how you build a track record when the MC is new.

None of this is complicated. It's just thinking through what you're doing and writing it down. Most brokers applying the 18-month rule aren't doing that — they're either auto-declining every new carrier regardless of history, or they're so focused on clearing the 18-month threshold that they're not actually looking at what those 18 months produced.

The rule is a heuristic. Like all heuristics, it's useful when you know why it exists, and dangerous when you treat it as a law.

— Mason Lavallet

Founder, DOTScreener.com