| NHTSA Rating Scale | 1 to 5 stars (5 is highest) (NHTSA New Car Assessment Program) |
| IIHS Rating Scale | Good, Acceptable, Marginal, Poor (Insurance Institute for Highway Safety) |
| IIHS Organization Type | Independent nonprofit, funded by auto insurers (IIHS) |
| NHTSA Frontal Crash Test Speed | 35 mph into a rigid barrier (NHTSA NCAP protocol) |
| IIHS Small Overlap Test Speed | 40 mph, 25% vehicle overlap (IIHS test protocols) |
| Top Safety Pick+ Headlight Requirement | Acceptable or Good rating required (IIHS award criteria) |
Two Rating Systems, Two Different Approaches
When you research a vehicle's safety, you'll typically encounter two sets of scores: stars from the National Highway Traffic Safety Administration (NHTSA) and grades from the Insurance Institute for Highway Safety (IIHS). Both are credible, but they test different things using different methods — and a vehicle can score well on one while performing only adequately on the other.
NHTSA is a federal government agency. Its New Car Assessment Program (NCAP) uses a star scale from one to five to rate vehicles in frontal, side, and rollover crash scenarios. Five stars is the highest possible score, and NHTSA publishes separate ratings for driver, front passenger, and rear passengers rather than a single overall number.
IIHS is an independent, nonprofit organization funded by auto insurers. Instead of stars, it assigns ratings of Good, Acceptable, Marginal, or Poor across a range of test categories. Its most recognized designations are the Top Safety Pick and Top Safety Pick+ awards, which require high marks across multiple categories including headlight performance.
| NHTSA Rating Scale | 1 to 5 stars (5 is highest) (NHTSA New Car Assessment Program) |
| IIHS Rating Scale | Good, Acceptable, Marginal, Poor (Insurance Institute for Highway Safety) |
| IIHS Organization Type | Independent nonprofit, funded by auto insurers (IIHS) |
| NHTSA Frontal Crash Test Speed | 35 mph into a rigid barrier (NHTSA NCAP protocol) |
| IIHS Small Overlap Test Speed | 40 mph, 25% vehicle overlap (IIHS test protocols) |
| Top Safety Pick+ Headlight Requirement | Acceptable or Good rating required (IIHS award criteria) |
Understanding both systems gives you a fuller picture. For a deeper look at the technologies these tests evaluate, see our breakdown of modern car safety systems.
What Each Test Actually Measures
NHTSA's frontal crash test involves driving the vehicle into a rigid barrier at 35 mph — simulating a head-on collision. Its side crash tests include a moving deformable barrier strike and a pole test. The rollover resistance rating is calculated from a dynamic handling maneuver and a static stability factor based on the vehicle's center of gravity.
IIHS runs a different set of scenarios designed to reflect real-world crash patterns. These include:
- Small overlap front: 25% of the vehicle's front hits a rigid barrier at 40 mph — one of the most lethal real-world crash types
- Moderate overlap front: 40% overlap at 40 mph
- Side (updated barrier): Simulates a larger SUV or truck striking the side of the test vehicle
- Roof strength: Measures resistance to crush in a rollover
- Head restraints and seats: Rates whiplash protection in rear-end collisions
- Headlights: Evaluated separately; poor headlights can prevent a vehicle from earning Top Safety Pick awards even with otherwise strong crash scores
IIHS also rates the effectiveness of a vehicle's optional and standard front crash prevention systems in vehicle-to-vehicle and vehicle-to-pedestrian scenarios. Active and passive safety features each play a role in how these scores come together.
NHTSA NCAP
The National Highway Traffic Safety Administration's New Car Assessment Program, which rates vehicles on a one-to-five star scale across frontal, side, and rollover crash tests. It is a federally run program.
IIHS Top Safety Pick+
The highest safety designation awarded by the Insurance Institute for Highway Safety. It requires Good ratings in all crash tests, an advanced or superior front crash prevention rating, and acceptable or good-rated headlights.
Small Overlap Front Test
An IIHS crash scenario where 25% of a vehicle's front corner strikes a rigid barrier at 40 mph. It targets a crash geometry that full-width frontal tests can miss, and it's closely associated with real-world fatalities.
Static Stability Factor (SSF)
A measurement NHTSA uses to estimate rollover risk. It is calculated from the vehicle's track width and center of gravity height — a wider, lower vehicle generally has a higher SSF and lower rollover tendency.
Front Crash Prevention Rating
An IIHS evaluation of how effectively a vehicle's automatic emergency braking system reduces or avoids collisions with other vehicles and pedestrians in controlled test conditions.
Roof Strength Test
An IIHS test that measures how much force a vehicle's roof can withstand before crushing. A stronger roof reduces the risk of serious head and neck injuries in rollover crashes.
How to Read the Scores Side by Side
The most important thing to understand is that a five-star NHTSA rating and an IIHS Good rating are not the same measurement expressed differently — they come from separate tests with separate methodologies. A vehicle could earn five NHTSA stars but receive a Marginal IIHS rating on the small overlap front test if its structure doesn't perform well in that specific scenario.
When evaluating a vehicle, look at both systems together:
- Check NHTSA's star ratings by occupant position — especially if you frequently carry rear-seat passengers
- Review each IIHS category individually, not just the overall award status
- Pay specific attention to the headlight rating and front crash prevention score, which are easy to overlook
- Note whether the tested trim matches what you're considering buying — NHTSA and IIHS test specific configurations, and a higher or lower trim may have different equipment
If a vehicle you're researching triggers a dashboard warning related to its safety systems, understanding your warning lights can help you respond appropriately.
Safety ratings provide useful comparative data but cannot guarantee outcomes in any individual collision. Always consult official NHTSA and IIHS databases for the most current test results on specific vehicle configurations.