Understanding the Safety Measurement System (SMS) Methodology

What Is the Safety Measurement System?

The Safety Measurement System (SMS) is the data-driven methodology used by the Federal Motor Carrier Safety Administration to identify motor carriers that pose the greatest safety risk. SMS analyzes on-road safety performance data collected during roadside inspections and from state-reported crash reports to quantify each carrier's safety performance across seven Behavior Analysis and Safety Improvement Categories (BASICs).

The SMS is the analytical engine behind the Compliance, Safety, Accountability (CSA) program. It runs monthly, recalculating every carrier's scores based on the most recent 24 months of safety event data.

Data Sources

SMS draws on two primary data sources:

• Inspection data -- violation records from roadside inspections conducted by state and federal law enforcement officers, reported through the FMCSA inspection system
• Crash data -- state-reported crash records meeting the DOT reportable threshold (fatality, injury with off-scene treatment, or disabling vehicle damage with tow-away)

These records are matched to individual motor carriers by their USDOT number. Carriers that have not had enough safety events (inspections or crashes) in the 24-month lookback window may not receive a percentile ranking in certain BASICs due to insufficient data.

How Scores Are Calculated

The SMS scoring methodology follows a multi-step process:

Step 1: Violation Severity Weighting

Each violation observed during an inspection is assigned a severity weight on a scale from 1 to 10 based on how strongly the violation relates to crash risk. For example, a driver operating with a suspended CDL receives a higher severity weight than a minor paperwork violation. The severity weights are published in the SMS methodology documentation and updated periodically as FMCSA refines its crash risk models.

Step 2: Time Weighting

More recent violations are weighted more heavily than older ones. The 24-month lookback window is divided into three segments:

1. Most recent 6 months: violations receive a time weight of 3
2. 6 to 12 months ago: violations receive a time weight of 2
3. 12 to 24 months ago: violations receive a time weight of 1

This time weighting ensures that the SMS prioritizes current safety performance over older history, rewarding carriers that have recently improved.

Step 3: Total BASIC Measure

For each BASIC, the total measure is calculated by summing the products of severity weight and time weight for all applicable violations, then dividing by the carrier's exposure measure (typically the number of relevant inspections or power units). This normalization allows fair comparison between carriers of different sizes.

Step 4: Safety Event Grouping

Carriers are grouped with peers that have a similar number of safety events (inspections). This safety event grouping ensures that a small carrier with 5 inspections is compared against other carriers with a similar number of inspections, rather than against large carriers with hundreds of inspections.

Step 5: Percentile Ranking

Within each safety event group, carriers are ranked from 0 to 100. A percentile of 90 means the carrier performs worse than 90% of its peers in that BASIC. FMCSA uses intervention thresholds -- typically 65% or 80% depending on the BASIC and carrier type -- to identify carriers that warrant further attention.

Monitoring Your SMS Scores

Carriers should regularly review their BASIC percentiles and the underlying violation data that drives those scores. Understanding which violations carry the highest severity weights allows carriers to prioritize corrective actions where they will have the greatest impact. Explore your carrier's safety data on TruckCodes and track trends over time using TruckCodes Research.