When people ask which violation is "most common," they usually get one list back. That list is useful, but it hides the number that decides whether a driver loses the rest of the day: what happens after the inspector writes the code. Two columns matter here. How often a code appears, and how often it puts the vehicle out of service (OOS). I'll go through both using the numbers in our dataset. The broader series of analyses is in the insights section.
The categories
Vehicle Maintenance dominates the raw count in this dataset with 15,233,046 violations. Hours-of-Service Compliance has 2,223,914, and Unsafe Driving has 1,713,588. Counts alone don't tell you much, so here is the OOS side for each BASIC:
- Vehicle Maintenance: 3,303,635 OOS, about 21.7% of its violations.
- Driver Fitness: 662,839 OOS out of 1,104,639, about 60%.
- Controlled Substances/Alcohol: 51,517 OOS out of 52,899, about 97%.
- Hazardous Materials Compliance: 46,271 OOS out of 160,441, about 29%.
- Hours-of-Service Compliance: 476,873 OOS out of 2,223,914, about 21%.
- Unsafe Driving: 336 OOS out of 1,713,588, about 0.02%.
That last line is the one to sit with. Unsafe Driving is the largest BASIC by a wide margin on the citation side, yet almost none of its violations remove a vehicle from the road at the roadside. The enforcement weight of those violations lands somewhere other than the parking brake.
The most-cited codes
These are the top five by raw count:
| Code | Description | Violations | Severity weight | |---|---|---|---| | 393.9 | Inoperable Required Lamp | 1,141,810 | 2 | | 393.47(e) | Brake Out of Adjustment (Roto, Clamp, DD-3, or Bolt) | 617,809 | 4 | | 396.17(c) | Operating a CMV without proof of a periodic inspection | 588,710 | 4 | | 396.17C-PI | Operating a CMV without documentation of a periodic inspection | 417,837 | 4 | | 393.95(a) | No/discharged/unsecured fire extinguisher | 374,204 | 2 |
Two things stand out. First, the lamp code leads the list by a wide margin, which is the kind of violation that is cheap to fix and easy to miss on a walk-around. Second, the two periodic inspection codes together account for 1,006,547 violations. They are separate codes in this dataset, one for proof and one for documentation, and I'm not going to guess at why they are split. Both are paperwork-side failures that a carrier can prevent with a tracking system.
The out-of-service line is a different list
Now sort the same dataset by OOS rate, which is the share of a code's violations that resulted in the vehicle being placed out of service:
- 396.3A1BOS (brake, defective brakes equal to or greater than 20% of service brakes): 278,496 violations, 277,706 OOS, 99.7%
- 393.43DBMA (breakaway not attached to the towing vehicle): 99.1%
- 393.9A-LSLIWR (both stop lamps inoperative when required on): 99.0%
- 383.23(a)(2) (operating a CMV without a CDL): 98.9%
- 393.41-BNPB (inoperative or missing parking brake on power unit): 98.8%
Brakes are the story on this list. Four of the top five codes involve brakes or a required-on lighting function, and the brake codes at the top are nearly always OOS when written. The rule to take from this is simple: if an inspector writes a brake code, expect the truck to stop there.
Notice that 396.3A1BOS is 10th by raw count and first by OOS rate. Notice also that the lamp code 393.9, the most-cited violation overall, does not appear in the top ten by OOS rate. Those two facts together are the reason to read both columns.
Severity weight is not the same as OOS
In this dataset, 396.3A1BOS carries a severity weight of 0, while the tire flat code 393.75(a)(3) carries a weight of 8, and the turn signal 393.9TS carries 6. If you read severity weight as "how dangerous," you would rank the brake code near the bottom, which contradicts its 99.7% OOS rate. I report the weight as stored in our data and don't have more detail on how it is assigned, so I would not use it to rank risk without checking the source behind it.
What I would take from this
- Brakes deserve more pre-trip time than their count suggests. The brake codes show up on both lists: 393.47(e) for adjustment, and 396.3A1BOS, 393.43DBMA, 393.43D-B, and 393.41-BNPB for the failures that end a trip.
- Lamps are high-volume, low-cost fixes. The 1.14 million violations on 393.9 show that a dead lamp is the most common thing an inspector writes. It is also the thing a driver can check in 60 seconds.
- Periodic inspection paperwork is a big slice of the count. Carry the proof, and check it before dispatch.
- Driver-side credential failures are almost always OOS. 383.23(a)(2) and 383.23A2-LCDLN both run above 98%.
One caveat. These numbers describe the violations in the dataset, not the odds that any particular carrier gets cited. The dataset doesn't give me inspection-level denominators for every code, so I'm careful not to turn these counts into a per-inspection risk rate.
If you want to look up a specific code, read its full description, and see how it is written before you build your pre-trip list, start with the violations lookup.
Key takeaways
- Vehicle Maintenance has the most violations, but Unsafe Driving has only 336 OOS out of 1,713,588.
- 393.9 Inoperable Required Lamp is the most-cited code at 1,141,810 violations, but it is not in the top ten by OOS rate.
- 396.3A1BOS is the top OOS code at 99.7%, even though it ranks 10th by count.
- Severity weight in this dataset does not track OOS rate. Check the code, not just the weight.