Key Takeaways
Option A
NHTSA (New Car Assessment Program)
The federal government's star-based vehicle safety rating system.
Best for: Consumers who want a single, government-backed numerical score covering frontal, side, and rollover performance.
Option B
IIHS (Insurance Institute for Highway Safety)
The insurance-industry-funded programme focused on real-world crash scenarios.
Best for: Consumers who want detailed, scenario-specific ratings that reflect how vehicles perform in common real-world collisions.
If you want a quick, government-standardised benchmark across all vehicle categories
NHTSA (New Car Assessment Program)
NHTSA's star ratings are federally mandated, consistently applied, and prominently displayed on window stickers, making them an efficient first-pass screen.
If you want granular insight into how a vehicle handles real-world crash types
IIHS (Insurance Institute for Highway Safety)
IIHS tests a broader range of scenarios — including small overlap frontal and side pole impacts — and rates headlights and ADAS, providing finer-grained safety detail.
If you are evaluating a vehicle for family use and want the fullest safety picture
IIHS (Insurance Institute for Highway Safety)
The IIHS Top Safety Pick+ award criteria incorporate multiple crash tests plus active safety technology, which is particularly relevant for protecting all occupants.
If you want to compare vehicles across model years using a consistent historical record
NHTSA (New Car Assessment Program)
NHTSA's programme has tested vehicles since 1978, offering a longer longitudinal dataset useful for comparing older and newer model performance trends.
Two Programmes, Two Different Missions
When a vehicle earns five NHTSA stars but only an "Acceptable" rating from the IIHS on a comparable test, drivers understandably wonder which result to trust. The answer is that both results are valid — they are simply measuring different things, using different methods, for different purposes.
NHTSA's New Car Assessment Program (NCAP) is a federal programme administered by the National Highway Traffic Safety Administration. Its tests are defined by regulation, its results appear on the Monroney window sticker, and its primary objective is to give consumers a standardised government benchmark. IIHS, by contrast, is an independent, non-profit organisation funded by auto insurers. Because its budget comes from the insurance industry — which has a financial stake in reducing crash severity and frequency — IIHS can continually update its tests to reflect emerging real-world crash patterns without waiting for a rulemaking cycle.
For a broader look at how the two organisations are structured and why both exist, see NHTSA and IIHS: The Two Systems That Define Vehicle Safety in America.
| Criterion | NHTSA NCAP | IIHS |
|---|---|---|
| Funding & governance | Federal government agency | Non-profit, insurance-industry funded |
| Rating scale | 1–5 stars per category | Good / Acceptable / Marginal / Poor |
| Primary frontal test | Full-width barrier, 35 mph | 40% offset barrier + small overlap (25%) |
| Side impact barrier | Moving deformable barrier (MDB) | Updated MDB replicating SUV/truck front |
| Rollover evaluation | Yes — dynamic handling test | Not part of core test battery |
| Headlight rating | Not included in star rating | Rated Good to Poor; affects TSP awards |
| ADAS / active safety | Separate optional evaluation | Rated; required for TSP+ award |
| Programme history | Testing since 1978 | Testing since 1995 |
Where the Test Methods Diverge
The core reason scores diverge is that the two programmes use fundamentally different crash configurations.
NHTSA conducts a full-width frontal barrier test at 35 mph, a side moving-barrier test, a side pole test, and a rollover resistance evaluation. Results from these tests combine into an overall star rating, with sub-scores available for each test category. The full-width frontal test distributes impact force evenly across the entire front of the vehicle — a configuration that tends to be relatively forgiving for structural performance.
IIHS tests vehicles against a 40% offset deformable barrier in its moderate overlap test, which concentrates impact force on one corner of the vehicle. More significantly, it introduced the small overlap frontal test in 2012, targeting the outermost 25% of the vehicle's front end. This scenario replicates what happens when a vehicle clips a telephone pole or the corner of another vehicle — a crash type that was exposing structural weaknesses not visible in full-width testing. The result: several vehicles that performed well on NHTSA's full-width test earned "Marginal" or "Poor" ratings on IIHS's small overlap test.
IIHS has also added a passenger-side small overlap test and updated its side test to use a taller, heavier barrier representing the growing prevalence of SUVs and pickups as striking vehicles. For a detailed breakdown of every IIHS scenario, see Small Overlap, Moderate Overlap, Side Pole: A Field Guide to IIHS Test Scenarios.
25%
Front-corner overlap in IIHS small overlap test
IIHS designed the small overlap test to replicate crashes involving only the outermost quarter of the vehicle's front end — a scenario full-width federal tests do not capture.
2012
Year IIHS introduced small overlap frontal test
When IIHS introduced the small overlap test, a significant share of vehicles that previously earned top marks in federal tests initially received "Marginal" or "Poor" ratings.
4
IIHS descriptive rating tiers
IIHS rates each test individually across four tiers — Good, Acceptable, Marginal, and Poor — allowing consumers to identify specific structural weaknesses by crash scenario.
Rating Scales: Stars vs. Descriptive Tiers
The two programmes also communicate results differently. NHTSA assigns one to five stars for each test category and an overall vehicle score. A five-star rating indicates the lowest probability of injury in that specific test; a one-star rating indicates the highest. The scale is intuitive but can compress meaningful performance differences — the gap between a "borderline" four-star vehicle and a strong four-star vehicle is not visible to the consumer.
IIHS uses a four-tier descriptive scale: Good, Acceptable, Marginal, and Poor. These ratings are applied individually to each test, so a vehicle can be rated "Good" on moderate overlap but "Poor" on small overlap. This granularity helps consumers identify specific structural vulnerabilities. IIHS also awards Top Safety Pick and Top Safety Pick+ designations based on meeting thresholds across multiple tests plus headlight performance — a factor absent from NHTSA star ratings entirely. For quick definitions of each IIHS tier, see IIHS Rating Categories at a Glance.
TSP+ Awards Change Annually
IIHS revises its Top Safety Pick and Top Safety Pick+ award criteria each model year, often raising the bar for headlights or adding new test requirements. A vehicle that earned TSP+ in one model year may not qualify in the next without structural or lighting updates. Always check the IIHS website for the criteria applicable to the specific model year you are evaluating.
How to Read Both Sets of Results Together
Neither programme is a complete picture on its own. A practical approach is to use NHTSA stars as an initial filter — vehicles with fewer than four stars in a specific category warrant closer examination — and then consult the full IIHS scorecard for scenario-by-scenario detail.
Pay particular attention to any IIHS test where a vehicle scores "Marginal" or "Poor" even if its NHTSA star rating appears strong. These divergences often point to specific structural or design vulnerabilities that the full-width federal test does not expose. Conversely, a vehicle with a lower NHTSA score in rollover resistance may still perform well across all IIHS crash tests — rollover resistance is not part of IIHS's core evaluation.
Also consider headlights. IIHS rates headlight performance on a "Good" to "Poor" scale because poor nighttime visibility is a meaningful crash risk factor. NHTSA's current star rating does not include a headlight evaluation, so a five-star NHTSA vehicle may still have headlights rated "Poor" by IIHS. For context on how these scores translate across vehicle categories, see Reading a Sedan's Safety Rating and What Crash Test Ratings Actually Measure.