How the ISS Algorithm Works

A comprehensive guide to understanding how FMCSA calculates your Inspection Selection System score and BASIC percentiles.

What is the ISS Score?

The Inspection Selection System (ISS) is a tool used by roadside inspectors to identify which motor carriers should be prioritized for safety inspections. The ISS provides a score from 1 to 100, with higher scores indicating a higher likelihood of being selected for inspection.

Key Point: The ISS score is not the same as your BASIC percentiles. ISS is used by inspectors to prioritize inspections, while BASIC percentiles show your safety performance relative to other carriers.

The ISS considers multiple factors including:

How ISS Scores Are Calculated

FMCSA uses a proprietary algorithm that weighs multiple safety indicators. While the exact formula isn't public, we know these factors contribute:

Primary Factors

  1. BASIC Percentiles - Higher percentiles in any BASIC category increase your ISS score
  2. Time Weighted Violations - Recent violations count more than older ones
  3. Severity Weights - More severe violations have higher impact
  4. Inspection History - Carriers with poor inspection results get higher scores

ISS Score Categories

ISS Range Category Inspection Priority
75-100 Inspect High priority - likely to be inspected
50-74 Optional Moderate priority - inspector discretion
1-49 Pass Lower priority - less likely to be selected

The 7 BASICs Explained

FMCSA measures carrier safety across seven Behavior Analysis and Safety Improvement Categories (BASICs). Each BASIC has its own percentile ranking from 0-100, with higher percentiles indicating worse safety performance.

🚗 Unsafe Driving

Threshold: 65%

Speeding, reckless driving, improper lane changes, inattention, failure to use seatbelt, and other dangerous driving behaviors.

⏰ HOS Compliance

Threshold: 65%

Hours-of-Service violations including exceeding driving limits, falsifying logs, operating without a valid log, and ELD violations.

👤 Driver Fitness

Threshold: 80%

Unqualified or unfit drivers including invalid CDL, medical certificate issues, and lack of required endorsements.

🍺 Controlled Substances

Threshold: 80%

Drug and alcohol violations including positive tests, refusals to test, and impaired driving violations.

🔧 Vehicle Maintenance

Threshold: 80%

Brake defects, lighting issues, tire problems, and other mechanical failures discovered during inspections.

☢️ Hazmat Compliance

Threshold: 80%

Hazardous materials handling violations including placarding, shipping papers, packaging, and loading/unloading issues.

💥 Crash Indicator

Threshold: 65%

Based on crash history including frequency and severity. State-reported crashes are included regardless of fault determination.

HOS Compliance Deep Dive

Hours-of-Service violations are among the most common issues affecting carrier safety scores. Understanding how HOS affects your ISS score is critical.

Common HOS Violations

Important: HOS violations have high severity weights. A single egregious violation (like falsifying logs) can significantly impact your percentile more than multiple minor violations.

Time Weighting

FMCSA uses a time-weight system that gives more importance to recent violations:

This means recent violations hurt your score more, but also that cleaning up your record over 24 months will show improvement.

Intervention Thresholds

When a carrier's BASIC percentile exceeds certain thresholds, they become subject to FMCSA intervention. The thresholds vary by category and carrier type.

BASIC Category General Carriers Hazmat Carriers Passenger Carriers
Unsafe Driving 65% 60% 50%
HOS Compliance 65% 60% 50%
Driver Fitness 80% 80% 80%
Controlled Substances 80% 80% 80%
Vehicle Maintenance 80% 75% 65%
Hazmat Compliance N/A 80% N/A
Crash Indicator 65% 60% 50%
Exceeding Thresholds: If your percentile exceeds the threshold for your carrier type, you may receive warning letters, targeted inspections, or be subject to a compliance review.

What Does "Not Subject to Threshold" Mean?

You may see "Not Subject to Threshold" or "Insufficient Data" displayed for some BASIC categories. This occurs when:

Good News: "Not Subject to Threshold" is generally a neutral or positive indicator - it means you don't have enough negative data points to be ranked poorly in that category. However, it doesn't mean you're exempt from inspections.

Data Sufficiency Requirements

FMCSA requires minimum inspection data before calculating percentiles:

Hazmat Carriers: Special Considerations

Carriers with Hazardous Materials authorization are subject to different rules and lower intervention thresholds.

HM Authorization Types

When Hazmat Thresholds Apply

Lower intervention thresholds apply when:

HM Not Subject to Thresholds: Some carriers have HM authorization but don't regularly transport hazmat, or haven't had hazmat inspections. These carriers may show "Not Subject to HM Thresholds" - they still have HM authority but aren't being measured against the stricter standards due to insufficient hazmat inspection data.

How to Improve Your Scores

Improving your ISS score and BASIC percentiles takes time and consistent effort. Here are actionable steps:

Short-Term Actions

Long-Term Strategies

Remember: Violations drop off after 24 months. Consistent clean inspections over time will naturally improve your percentiles as old violations age out.

Check Your ISS Score Now

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