The seven categories
The Safety Measurement System sorts roadside inspection violations into seven behaviour categories, known as BASICs:
- Unsafe Driving — speeding, reckless driving, improper lane change, seat belt violations.
- Hours-of-Service Compliance — driving beyond permitted hours, logbook and ELD violations.
- Driver Fitness — licensing, medical certification and qualification file deficiencies.
- Controlled Substances and Alcohol — use or possession while operating.
- Vehicle Maintenance — brakes, lights, tyres, load securement, defect reporting.
- Hazardous Materials Compliance — placarding, packaging and handling of regulated materials.
- Crash Indicator — history of reportable crashes.
How a percentile is calculated
Violations are weighted by severity and by how recently they occurred, then normalised against exposure — roughly, how much the carrier is on the road and how often it is inspected. The result is compared against a peer group of carriers with a similar volume of inspections, and expressed as a percentile from 0 to 100.
A percentile of 75 does not mean the carrier failed three quarters of something. It means that within its peer group, three quarters of carriers had a better measure in that category.
Minimum data requirements
A category only produces a percentile once there is enough data to support one. Carriers below the threshold show no percentile in that BASIC even where violations exist. This is why a carrier with a handful of inspections often appears to have a nearly blank record — not because it is clean, but because the sample is too small to rank.
The corollary is that small carriers can swing dramatically. One inspection with several violations can move a low-volume carrier a long way up a percentile, and the same carrier may fall back just as sharply as the violation ages out of the window.
The twenty-four month window
Data rolls off after twenty-four months. Percentiles therefore change without any new event occurring, simply because older violations expire. A rising percentile means recent activity is worse than what it replaced; a falling one may mean improvement, or may mean an old cluster of violations has aged out.
Crash Indicator has a known limitation
The Crash Indicator counts reportable crashes without, in the public presentation, distinguishing who was at fault. A carrier struck from behind at a traffic light and a carrier that caused the same collision are recorded alike. A review process exists to flag not-at-fault crashes, but it is not automatic and not universally used.
This is worth stating plainly whenever crash data informs a decision.