IIHS tests Mercedes-Benz E-Class vs Smart FortwoEnlarge Photo
2) Star Ratings Don't Compare Across Weight Classes
This is one of the key points to keep in mind as you browse safety ratings. Even with the realignment of federal star ratings, a small hatchback with a five-star score might not provide the protection of a mid-size sedan also getting five stars. And that's even before considering issues with bumpers and crash structures that don't always meet up.
"Size and weight are important aspects of what happens in a crash," said the IIHS's Rader. "So a small car that gets top crash-test ratings isn't as safe as a large car with the same ratings."