What Is an ISS Score and Why Does It Matter?

The ISS score is one of the most widely referenced numbers in motor carrier risk assessment, yet many professionals who use it daily do not fully understand how it works. If you are an insurance underwriter, freight broker, or compliance analyst, this article will give you a clear, practical understanding of what ISS is, how it is calculated, and why it matters for your business.

What Is the ISS Score?

ISS stands for Inspection Selection System. It is an algorithm developed by FMCSA (the Federal Motor Carrier Safety Administration) to help roadside inspection officers decide which carriers and vehicles to inspect at weigh stations and during traffic stops.

The ISS score ranges from 1 to 100. A higher score means the carrier has a higher priority for inspection. In practical terms, carriers with high ISS scores are more likely to be pulled in for a full roadside inspection when they pass through a weigh station that uses the ISS system.

How Is the ISS Score Calculated?

FMCSA does not publish the exact formula for ISS, but the score is known to be derived from a carrier's BASIC percentile scores and other safety data. Key inputs include:

• BASIC percentiles — The carrier's percentile ranks across the seven Behavior Analysis and Safety Improvement Categories (BASICs), with greater weight given to categories that correlate most strongly with crash risk.
• Out-of-service (OOS) rates — The percentage of the carrier's inspections that result in an out-of-service order for the driver or vehicle.
• Inspection history — The volume and recency of the carrier's inspection activity. Carriers with very few inspections may receive elevated scores due to uncertainty.
• Crash history — The carrier's involvement in state-reported crashes, including the number, recency, and severity of those crashes.

The ISS algorithm synthesizes these inputs into a single composite number that reflects the carrier's overall safety risk profile. It is updated regularly as new inspection and crash data flows into the FMCSA system.

ISS vs. Individual BASIC Percentiles

A common question is how ISS differs from BASIC percentiles. The key distinction is:

• BASIC percentiles are category-specific. A carrier has a separate percentile for Unsafe Driving, HOS Compliance, Vehicle Maintenance, and so on. Each percentile tells you about performance in one dimension of safety.
• ISS score is a composite. It combines information from multiple BASICs (and other data) into a single number. Think of it as a weighted summary of the carrier's overall safety posture.

Both are useful, but they serve different purposes. BASIC percentiles are better for diagnosing specific areas of concern (for example, a carrier with a 92nd percentile in Vehicle Maintenance has clear equipment issues). ISS is better for a quick overall risk assessment and for comparing carriers against each other on a single scale.

How Insurance Underwriters Use ISS

In the trucking insurance industry, ISS has become a de facto standard for initial risk triage. Here is how it is typically used in underwriting workflows:

1. Automated screening — When a new application arrives, the underwriter pulls the carrier's ISS score. Many underwriting systems apply automatic thresholds: for example, ISS below 25 may qualify for streamlined approval, while ISS above 75 may trigger an automatic decline or mandatory manual review.
2. Portfolio monitoring — Insurers monitor ISS scores across their entire book of business. A carrier whose ISS jumps from 30 to 65 mid-policy may receive a loss control review or a non-renewal notice at the next policy period.
3. Pricing adjustments — Some actuarial models incorporate ISS directly as a rating factor, using it to adjust premiums within a given risk class.
4. Regulatory defense — In litigation following a trucking accident, plaintiffs often argue that the insurer should have known the carrier was high-risk. An ISS score on file at the time of underwriting provides documented evidence of the risk assessment process.

CarrierOk provides ISS scores through both the ISS Score API and the platform UI, enabling underwriters to integrate ISS into automated workflows or access it on-demand during manual review. Read more about how CarrierOk supports insurance underwriting use cases.

What ISS Score Should Trigger a Manual Review?

There is no universal answer, as risk tolerance varies across organizations. However, common industry practices include:

• ISS 1-25 — Generally considered low risk. Many organizations auto-approve carriers in this range, subject to other checks (authority status, insurance, chameleon signals).
• ISS 25-50 — Moderate risk. Some organizations apply standard review, others auto-approve with conditions.
• ISS 50-75 — Elevated risk. Most organizations require manual review before approval. The underlying BASIC percentiles should be examined to understand which categories are driving the score.
• ISS 75-100 — High risk. Many organizations decline or require extensive review. Carriers in this range are the most likely to be selected for roadside inspection by FMCSA.

Regardless of where you set your threshold, the key is to pair ISS with the underlying BASIC percentiles. An ISS of 60 driven primarily by Vehicle Maintenance issues tells a very different story than an ISS of 60 driven by Unsafe Driving or Controlled Substances violations.

Does ISS Include the Crash Indicator?

Yes. Unlike the public-facing SMS portal, which hides Crash Indicator and Hazmat Compliance percentiles, the ISS algorithm uses data from all seven BASICs including Crash Indicator. This is one reason ISS is considered a more complete risk signal than looking at the five public BASIC percentiles alone.

However, because ISS is a composite, you cannot tell from the ISS number alone which BASICs are contributing the most. This is why CarrierOk provides both ISS scores and all 7 BASIC percentiles — so you can see the summary and the breakdown.

Accessing ISS Scores Programmatically

FMCSA does not offer a public API for ISS scores. The ISS system is primarily an internal tool used at roadside inspection points. However, CarrierOk computes ISS-equivalent scores using the same underlying data and methodology, and makes them available through our ISS Score API.

API responses include the ISS score alongside all 7 BASIC percentiles, authority status, insurance details, and 50+ proprietary risk signals — everything you need for a complete carrier risk assessment in a single API call.

Start a free trial and pull your first ISS score in minutes.