Direct automotive answer
What is the difference between NHTSA and IIHS ratings?
They are separate programs with different tests, scoring and applicability rules. Do not combine their labels into one rating. This safety, ratings and recalls answer depends on Test protocol, Model year, Award criteria, Headlight variation. Confirm each against the exact vehicle rather than assuming a class-average figure. The sections below break this down further: what each emphasises, using them together, two independent programmes. 5 related follow-up questions are answered separately below, each with its own conditions attached. This site reviews every answer under a configuration-first standard, verified against NHTSA datasets and APIs and linked to related safety, ratings and recalls questions for the adjacent decisions this one usually raises. It sits within a safety, ratings and recalls library of 8 related questions, held to the same configuration-first standard.
NHTSA runs the federal five-star programme. IIHS is an independent insurance-industry organisation running its own tests under different protocols with its own award structure.
They evaluate overlapping but distinct scenarios, so strong results in one do not guarantee strong results in the other. Consulting both gives a fuller picture than either alone.
What each emphasises
The programmes were designed for different purposes and evolved differently.
- NHTSA: frontal, side and rollover, combined into an overall star rating
- IIHS: includes small-overlap frontal tests, roof strength and side impacts under its own protocols
- IIHS also evaluates headlights, which vary substantially by trim
- IIHS assesses crash-avoidance technology and seat-belt reminders separately
- Neither rates every configuration of every vehicle
Using them together
Check both for the same model year and configuration, and note where one has tested a vehicle the other has not.
Remember that a rating from either programme is not a substitute for checking open recalls by VIN, which is a live condition instead of a test result.
Two independent programmes
NHTSA is the federal regulator and runs the 5-Star Safety Ratings programme, testing frontal, side and rollover resistance. IIHS is an independent organisation funded by insurers, running its own set of crash and crash-avoidance evaluations.
They use different tests, different criteria and different scales, so a strong result in one does not automatically predict the other. Reading both gives a fuller picture than either alone.
- NHTSA: federal regulator, 5-star scale
- IIHS: independent, insurer-funded, its own award structure
- Different tests, criteria and scales
- Reading both is more informative than either alone
What changes the answer
- Test protocol
- Model year
- Award criteria
- Headlight variation
Common follow-up questions
Which rating is more important?
Neither replaces the other. They test different scenarios, so reading both for the same configuration gives the fuller picture.
Why does IIHS rate headlights?
Because headlight performance affects real-world crash risk and varies substantially by trim, which makes it a meaningful safety difference within one model line.
Can a car do well in one and poorly in the other?
Yes, because the protocols differ. That divergence is itself informative and worth reading, not averaging away.
Can I compare star ratings across vehicle sizes?
No. Ratings compare vehicles within a weight and size class. Two five-star vehicles from different classes are not equivalent in a collision between them.
Which rating should I trust?
Both, for different things. They use different tests and criteria, so a strong result in one does not automatically predict the other.
Related questions
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