Two Agencies, Two Missions
When you see a safety rating attached to an SUV or truck, it almost certainly comes from one of two organizations: the National Highway Traffic Safety Administration (NHTSA) or the Insurance Institute for Highway Safety (IIHS). They are not the same entity, and their results don't always agree.
NHTSA is a federal agency within the U.S. Department of Transportation. Its New Car Assessment Program (NCAP) sets minimum safety standards and issues star ratings that manufacturers are legally required to disclose. IIHS, by contrast, is an independent nonprofit funded by auto insurers. It develops its own tests independently of federal requirements — often more demanding ones — with the goal of reducing crash deaths and injuries. Understanding who runs each programme shapes how you interpret the numbers they produce. For a broader look at how ratings compare across global programmes, see how Euro NCAP and ANCAP ratings work.
NHTSA
The National Highway Traffic Safety Administration — a U.S. federal agency that sets minimum vehicle safety standards and publishes star-based crash ratings through its New Car Assessment Program.
IIHS
The Insurance Institute for Highway Safety — an independent nonprofit funded by auto insurers that conducts its own crash tests and issues Good-to-Poor ratings, often using more demanding scenarios than federal standards require.
Crashworthiness
How well a vehicle protects its occupants once a crash has already occurred — the primary focus of both NHTSA and IIHS crash tests.
Small Overlap Test
An IIHS crash scenario where only 25% of the vehicle's front corner strikes a rigid barrier, replicating a common real-world collision that can bypass a vehicle's main structural frame.
Static Stability Factor
A mathematical measure NHTSA uses to estimate rollover risk, calculated from a vehicle's track width and center-of-gravity height — taller, narrower vehicles score lower.
Top Safety Pick+
The IIHS's highest vehicle safety designation, awarded only to vehicles that meet Good or Acceptable thresholds across multiple crash tests and also earn high marks for headlight performance.
Compatibility
How well a vehicle's structure aligns with other vehicles it may collide with. Poor compatibility — common with tall trucks — can increase injury risk to occupants of smaller vehicles in the same crash.
How NHTSA Tests Vehicles
NHTSA evaluates vehicles across three broad categories, each contributing to an overall star score from one to five:
- Frontal crash: A full-width barrier test at 35 mph simulating a head-on collision. NHTSA measures injury risk to the driver and front passenger.
- Side crash: A moving deformable barrier strikes the vehicle at the driver's door at 38.5 mph, simulating an intersection T-bone scenario.
- Rollover resistance: Rather than a physical tip test, NHTSA uses a dynamic handling maneuver and a static stability factor based on track width and center of gravity height. The result is a star rating from one to five, where five stars indicates the lowest rollover risk.
NHTSA also conducts a pole-side impact test and evaluates ease of child safety seat installation. Its ratings are publicly searchable at safercar.gov. Keep in mind that NHTSA's tests are designed to set a safety floor — vehicles that score five stars have exceeded the minimum standard, but five stars does not mean the vehicle performed well in every conceivable crash scenario.
How IIHS Tests Vehicles
IIHS uses a Good / Acceptable / Marginal / Poor rating scale across a wider range of test scenarios. Its programme has historically pushed the industry on structural performance in ways federal standards initially did not require.
- Moderate overlap frontal: 40% of the vehicle's front-left corner strikes a deformable barrier at 40 mph — a common real-world crash pattern.
- Small overlap frontal (driver and passenger side): Only 25% of the front corner hits a rigid barrier at 40 mph. This test, introduced in 2012, exposed structural weaknesses in many vehicles that had earned top NHTSA scores.
- Side barrier and side pole: A moving barrier simulates an intersection crash; a pole test addresses narrow-object intrusion like a tree or utility pole.
- Roof strength: A plate presses down on the roof at a standardized rate; IIHS measures how much load the structure sustains before significant crush.
- Head restraints and seats: Whiplash protection in rear-end collisions.
- Headlights: Rated separately on a Good to Poor scale based on visibility range at night — a category that significantly affects real-world safety but is absent from NHTSA ratings.
IIHS also evaluates vehicle-to-vehicle crash prevention systems and pedestrian detection. Its Top Safety Pick and Top Safety Pick+ designations require meeting thresholds across multiple categories simultaneously. Note that crash ratings and driver-assistance features are evaluated separately — as explained in our article on how safety ratings and safety features differ.
Why SUVs and Trucks Present Unique Challenges
Body style matters in crash testing. SUVs and trucks introduce variables that sedans and hatchbacks don't face to the same degree.
Rollover risk is the most significant. Taller vehicles with a higher center of gravity are inherently more prone to rolling over in emergency maneuvers or tripped scenarios (where a tire catches a curb or soft shoulder). NHTSA's rollover star ratings reflect this directly — trucks and body-on-frame SUVs often score lower than crossovers built on car platforms. Vehicle construction also plays a role; see our overview of body-on-frame vs. unibody construction for context on how architecture affects crash behavior.
Compatibility is a second concern. When a large truck or SUV collides with a smaller passenger car, the geometric mismatch — different bumper heights, different structural rails — can cause the larger vehicle to override the smaller one's crumple zone, dramatically increasing injury risk to occupants of the smaller vehicle. IIHS has worked with manufacturers on bumper height standards specifically because of this issue.
Cab and bed configurations for trucks add further complexity. Extended-cab and crew-cab variants often have different structural characteristics than regular cabs, and ratings from one configuration don't automatically transfer to another.
Check Each Configuration Separately
Ratings for a crew-cab truck may not apply to a regular-cab version of the same model, and vice versa. When using NHTSA or IIHS databases, filter by the exact body style and model year you're considering — don't assume one rating covers every variant in a manufacturer's lineup.
Reading Ratings Side by Side
The most practical approach when researching any SUV or truck is to look up both NHTSA and IIHS results for the specific model year you're evaluating. A vehicle can earn five NHTSA stars while receiving a Poor IIHS small-overlap rating — this has happened with real production vehicles. The inverse is also possible.
When comparing results, pay attention to:
- Which model year was tested. A 2021 rating does not apply to a 2019 vehicle, even if the exterior looks identical.
- Whether the trim level affects the rating. Some safety equipment — like side curtain airbags or electronic stability control — may be standard on one trim and optional on another, potentially affecting how the vehicle performs.
- Headlight ratings from IIHS. This is one of the most practically meaningful ratings for everyday driving and is easy to overlook.
For a structured approach to comparing vehicles across multiple dimensions before you buy, the Research & Compare hub covers frameworks that go beyond safety alone. And if you're evaluating a used vehicle, check our new vs. used car tradeoffs guide — safety ratings on older models may reflect outdated test protocols that have since been revised.
This article provides general educational information about vehicle safety rating programmes. It does not constitute a safety guarantee for any specific vehicle. Always consult official NHTSA and IIHS databases for the most current ratings.
