The 18-Month Rule Has No Legal Basis. Here's How to Use It Anyway.

Three years ago I turned down MC-1394728 — a carrier out of Nashville, 11 months old, running dry van — because they didn't clear my 18-month threshold. Solid dispatcher on the phone. Forty-some-thousand dollars in general commodities going to a distribution center in Atlanta. Load that would have fit their equipment perfectly.

They found another broker. Over the next 14 months they completed 40 clean loads, not one cargo claim. When I ran into their dispatcher at a terminal show, he remembered me. I'd passed on a carrier that had no business being passed on.

The 18-month rule cost me a relationship for no reason I could actually articulate.

The Rule Isn't in Any CFR

Search Title 49 for "18 months" in the context of new carrier authority. You won't find it as a vetting standard. The Federal Motor Carrier Safety Regulations don't set 18 months as the threshold at which a carrier becomes safe to book. No FMCSA guidance memo refers to it. No case law holds it up as the industry standard. It's a convention that spread through broker forums and compliance trainings until it became doctrine through repetition.

That doesn't mean it's useless. But it means you should understand what it's actually tracking before you apply it.

Where 18 Months Actually Came From

When a carrier registers with FMCSA and begins interstate operations, they enter the new entrant program under 49 CFR Part 385. FMCSA must complete a safety audit of that carrier within 12 months of registration. The audit covers the carrier's hours-of-service records, driver qualification files, vehicle maintenance program, and accident register. Pass it and you stay on the road; fail it and FMCSA moves to revoke or downgrade your authority.

So the industry reasoning goes: at 12 months, a carrier has just cleared federal review. Give them another six months to establish a real inspection record beyond the audit paperwork, and at 18 months you have something substantive to evaluate. That logic isn't wrong. The problem is how it gets applied.

What a broker is really trying to assess with the 18-month rule is data volume — specifically, whether the carrier has accumulated enough roadside inspections in FMCSA's Safety Measurement System for the available BASIC scores and OOS rates to be statistically meaningful. Time is a rough proxy for inspection count. But it's a bad proxy, because inspection volume depends on how actively the carrier is running, not on how long they've held authority.

When 14 Months Is the Right Carrier

MC-2193847, DOT-4738291, operating out of Memphis. Fourteen months in. Dry van, common carrier authority, interstate. I pull their SAFER snapshot: 31 roadside inspections, zero OOS violations. Driver Fitness BASIC at the 9th percentile — well below the 80th-percentile alert threshold. Unsafe Driving BASIC shows insufficient data for a percentile calculation, which at 14 months with 31 inspections most likely means zero Unsafe Driving violations in the measurement window. No crash history. Passed their new entrant safety audit at month 11 per the SMS Investigation tab.

The load in question: $62,000 in electronics on a 53-foot dry van, two-day transit, one driver named in the dispatch confirmation. Standard $1M cargo coverage confirmed on the L&I database.

This carrier is 14 months old. I have 31 inspections to evaluate. Their record is cleaner than a significant portion of the three- and four-year carriers I look at every week. The 18-month rule says turn them down. The actual inspection record says they've been doing this job right since the day they turned a wheel.

I'm booking them. And I'm documenting exactly why.

When 22 Months Should Stop You Cold

MC-3847162, DOT-5931047, 22 months old, out of Laredo. Flatbed. They've cleared the 18-month threshold, so most brokers would add them to their approved carrier list and move on.

What I see when I pull SAFER: 7 inspections total. Two of those resulted in OOS violations — one for brake adjustment, one for lighting defects. OOS rate: 28.6%. Vehicle Maintenance BASIC shows insufficient data for percentile calculation. Driver Fitness BASIC is also blank.

Seven inspections in 22 months. That carrier is not running at a volume that generates a meaningful safety record. The two OOS violations out of seven inspections is a terrible ratio. And it's not generating a BASIC alert because the inspection count is too low for the percentile system to engage — which means it looks quiet to any broker who's only scanning for alert flags.

The 18-month rule clears them. Their actual data tells a different story.

This is the structural failure in the binary cutoff: thin but alarming records slide through any time-based filter. A carrier with seven inspections at 22 months has the exact same data quality problem as a carrier with seven inspections at nine months. The calendar isn't the variable. Inspection count is.

What the Rule Is Actually Tracking

The real question isn't "how old is this authority?" It's whether this carrier has accumulated enough inspection history that the available data means something.

For FMCSA's BASIC percentile calculations, there are minimum inspection thresholds before a score generates at all. The specific minimums vary by BASIC category — you can find them in the SMS methodology documentation — but the general principle is that a carrier with two or three inspections won't show a percentile score. They'll show "insufficient data." That's not a clean record. That's no record.

My informal working threshold: I want to see at least 10 inspections in the 24-month SMS window before I treat a BASIC score as meaningful without a heavy discount for sample size. That's not a published FMCSA standard — it's a judgment call I've calibrated over time. Below that count, I'm treating the carrier like a new entrant regardless of what the calendar says.

A carrier with two years of authority and a part-time operation might have fewer inspections than a carrier eight months in running four trucks full-time. The calendar tells you how long they've been registered. The SMS tells you how much data you actually have. Those two numbers are different numbers.

The Montgomery Question

After the Supreme Court's unanimous decision in Montgomery v. Caribe Transport II — which held that the FAAAA does not preempt state-law negligent selection claims against freight brokers — the "was your vetting process reasonable?" question has real stakes. Brokers can now be sued in state court for booking the wrong carrier. Juries will decide whether your process met the standard of ordinary care.

A jury of twelve people who have never heard of CSA percentiles will not find "I have an 18-month rule" to be a compelling answer to "why did you book a carrier with a 28% OOS rate?" They will understand this: you had access to federal inspection records. You chose to filter by calendar date instead of reading them.

A binary time cutoff is not a due-diligence process. It's a shortcut that looks like a process. The difference matters under discovery.

The Three Additional Checks for Young Authority

When a carrier is under 18 months, I don't auto-decline. I do three things I might otherwise skip or do less thoroughly.

Inspection count and OOS rate, together. I want to see a minimum of 8–10 inspections before I treat the record as substantive. If they're at month 14 with 30 clean inspections, that's more reliable data than I have on some carriers with three years of authority. If they're at month 16 with 4 inspections, I'm treating them the same way I'd treat a two-month-old carrier.

New entrant audit status. The SMS Investigation tab in FMCSA's Safety Measurement System shows investigation history, including new entrant audits, with dates and outcomes. I want to see the audit listed as passed. If the carrier is under 12 months and the audit hasn't happened yet, I note that explicitly in the file and document that it hasn't cleared the first federal review.

FMCSA L&I insurance history. Young carriers with lapses or cancellations in their first 12 months are a serious flag. A new entrant that has already had one insurance cancellation is telling you something about their operation that their inspection record can't offset. I pull the L&I database — not just a COI from the broker — to see the full filing history.

None of these checks is unique to young authority. What's different is the degree of attention I pay to each signal when the overall data volume is thin. Thin data means any red flag counts more, because you have fewer green data points to weigh against it.

The Bigger Point: The Rule Goes Both Ways

Most brokers use the 18-month rule only in the direction of exclusion — if a carrier is under 18 months, decline. But the rule says nothing about carriers over 18 months. I've watched brokers turn down a clean 14-month carrier with 30 inspections and then book a 30-month carrier with a 20% OOS rate without a second look, because the older carrier cleared the age threshold.

That's backwards. The threshold cuts both ways. Once a carrier clears 18 months, you don't get to stop thinking. Their inspection history still tells you whether they're running a safe operation. A carrier that's been on the road for two years with 8 inspections and 2 OOS violations hasn't built a track record. They've built a thin, problematic record that the age threshold is hiding.

The 18-month rule is worth keeping. It's a reasonable starting point for increasing scrutiny on carriers with less than a full inspection cycle in the SMS window. But it's a trigger for closer review, not a substitute for it — and clearing it is not a clean bill of health.

How I Document This

For a carrier under 18 months that I approve: authority registration date, new entrant audit result and date (pulled from SMS Investigation tab), total inspection count, OOS violation count, OOS rate, any BASIC percentiles if available, and one sentence explaining why the inspection record is substantive enough to warrant approval despite the authority age. If the load has any elevated exposure — high-value cargo, hazmat, temperature-sensitive, tight delivery window — I add a note on any specific signals I looked at and found clean.

For a carrier under 18 months that I decline: authority registration date, inspection count, the specific data quality issue (usually insufficient inspection count for a meaningful record), and the decision. No elaboration required. The fact pattern is the reasoning.

For a carrier over 18 months that I flag for additional scrutiny due to thin inspection history: same structure, plus an explicit note that the age threshold was met but data volume was insufficient and I treated the carrier accordingly.

None of these is a long document. A few lines per load. The value isn't the length — it's the consistency. When discovery comes, the question isn't whether you wrote a novel about your vetting process. It's whether you can show that you applied a coherent, documented standard to every load. Carriers approved below the age threshold with a documented reason hold up better than carries approved above it with no documentation at all.

— Mason Lavallet

Founder, DOTScreener.com