Making Comparisons Between Car Safety Ratings

vehicle safety ratings are important to your familyWhen a subcompact 2016 Smart ForTwo and a full-size SUV 2016 Chevrolet Tahoe both get a 4-star overall safety rating, you have to know that something isn’t quite right with the existing systems for vehicle ratings. The Tahoe is nearly three times heavier, nearly twice as long, a full two feet wider, and more than a foot taller than the tiny ForTwo … can they really provide the same protection level?

When we took a look at real life crash data, the answer became clear. Two cars of very different sizes do not provide the same level of protection despite receiving the same car safety rating. While both vehicles score top ratings from other organizations, Auto Grades show a big difference between the Tahoe and ForTwo.

The Auto Professor gives the Tahoe an Auto Grade of A, and the Smart ForTwo gets a D.

So, What’s the Problem?

In a nutshell, the biggest problem with the traditional car safety ratings systems is that cars are rated using laboratory tests with results that can only be compared to other similar cars. We took a look at both of the organizations currently providing vehicle safety ratings in the US and here’s what we found:

NHTSA Star Ratings

The National Highway Traffic Safety Administration (NHTSA) is an agency under the US Department of Transportation. “Our mission is to save lives, prevent injuries, and reduce economic costs due to road traffic crashes, through education, research, safety standards, and enforcement.”

You’re probably most familiar with NHTSA’s car safety ratings – known as the 5 Star Safety Ratings Program. It ranks vehicles from 1 star (the lowest) to 5 stars (the highest). In theory, more stars equal safer cars, but read our post on star rating inflation for more about why this isn’t quite accurate.

NHTSA warns consumers that ratings should only be compared between vehicles with similar weight and class – within 250 lbs.

For example, the 2016 Smart ForTwo’s 4-star safety rating should only be compared to subcompact cars that weigh about 1,980 lbs (the approximate weight of the Smart car). So, what can the Smart car be compared to? According to our research, the list of rated subcompact cars of “similar size and weight” is short. One such car is the Mitsubishi Mirage, also 1,980 lbs. The Mirage also receives a 4-star safety rating but gets a D+ Auto Grade.

IIHS Safety Ratings

The Insurance Institute for Highway Safety (IIHS) is a non-profit organization that is wholly supported by insurance companies and associations. They operate with the mission to reduce deaths, injuries and property losses from motor vehicle crashes.

The IIHS vehicle safety rating system is also based on laboratory testing, but their tests and ratings are different from the NHTSA stars ( They assign vehicles a rating of Good, Acceptable, Marginal or Poor for each of their laboratory crash results.

Again, some of these ratings can only be compared within size and class categories. For car buyers, determining the size categories can be rather confusing because they are defined by both the weight and footprint – or shadow (length x width) – of the vehicle.

Using our previous example, while the NHTSA ratings allow you to compare the Smart ForTwo and Mitsubishi Mirage (their weights are within 250 lbs.), the IIHS classifies the 2016 Smart ForTwo as a ‘microcar’ and therefore cannot be compared to a Mitsubishi Mirage, a minicar.

As you can see, when it comes to comparing cars and their safety ratings, it can get pretty confusing!

When it comes to comparing cars and their safety ratings using the traditional rating systems—it can get pretty confusing! And unrealistic!

car safety ratings

Let’s Break This Down …

Consider a different example. Suppose you are interested in a midsize sedan, and you’re contemplating a 2016 Ford Fusion (which weighs about 3,460 lbs on average). Its federal star rating can be compared to the 2016 Toyota Camry (about 3,220 lbs) because it’s within 250 lbs of the Fusion’s weight (~240 lbs lighter).

But the Fusion cannot be compared to the 2016 Nissan Altima (about 3,110 lbs), since it weighs 350 lbs less – wider than the window prescribed by the federal tests.

All three midsize sedans receive 5-star overall safety ratings, but while the Fusion can be compared to the Camry and the Camry to the Altima, the Fusion cannot be compared to the Altima. Confusing, right? It’s also unrealistic.

The Auto Grades Advantage

Auto Grades do not require vehicles be of similar weight and class or size. All vehicles are graded in comparison to all other vehicles. You can use Auto Grades to compare subcompacts and midsize sedans and SUVs. We help you make the choices that make sense to you, without restrictions.

Plus, because Auto Grades are based on real people, not dummies, we can personalize our rankings to give you, the car buyer, distinctions in your choices. Automotive safety experts have known for decades that crash outcomes can have different results depending on occupant sex and age. Auto Grades uses this important information to help you pick the best vehicle for you, personally!

Get Your Auto Grade!

The bottom line is that not all vehicle safety ratings are created equal. We’re challenging the meaning of safety because we want you to make informed decisions based on real data. Get your free auto grade and see for yourself.

Working together to create a world where everyone walks away from a crash.