In the U.S., two organizations rate vehicle crash safety: the government’s National Highway Traffic Safety Administration (NHTSA), through its five-star New Car Assessment Program, and the insurance-funded Insurance Institute for Highway Safety (IIHS), known for its Top Safety Pick awards. They use different tests, and a car can score well with one and less well with the other. Importantly for chauffeured passengers, IIHS has increasingly examined rear-seat occupant protection, an area where many vehicles have lagged behind the front seats.

Side by side

NHTSA IIHS
Who U.S. government agency Independent, funded by insurers
Ratings 1–5 stars (frontal, side, rollover, overall) Good / Acceptable / Marginal / Poor; Top Safety Pick awards
Known tests Full frontal, side barrier, rollover resistance Small and moderate overlap frontal, updated side test, headlights, pedestrian AEB
Criteria Evolving Tightened frequently

NHTSA five-star ratings

NHTSA crashes cars into barriers and measures dummy injuries, and calculates rollover risk. Stars make comparison simple.

IIHS tests

IIHS pioneered tests that manufacturers didn’t design for, such as the small overlap frontal test, which hits only a corner of the car. It also rates headlights, crash avoidance systems and seat belt reminders, and has made its awards progressively harder to win.

The rear seat

Rear seats have historically received less engineering attention. IIHS added a dummy in the rear seat in its updated moderate overlap test and found that many vehicles protected rear passengers less well than front occupants — often because rear belts lack pretensioners and load limiters. Luxury cars like the S-Class have addressed this with rear airbags and inflatable belts. Read the S-Class rear-seat guide and airbag history.

What it means for passengers

Choose a service with modern vehicles, and always wear the rear seat belt. Read verify your ride: safety tips.