In a crash test of 11 of the smallest cars on the market, only one vehicle received an acceptable rating. The rest received marginal or poor ratings in the study, providing evidence that supports a widely held notion that smaller cars are among the least safe on the road.

No other vehicle group has performed as poorly on a new crash test than these mini cars, says the Insurance Institute for Highway Safety, the nonprofit group that conducted the testing. The latest results of which were released Wednesday. The Chevrolet Spark was the only car earning an overall "acceptable" rating on the small-front overlap test, and even that vehicle had its shortcomings, IIHS said.

"Small lightweight vehicles have an inherent safety disadvantage," said Joe Nolan, the senior vice president for vehicle research at IIHS. "That's why it's even more important to choose one with the best occupant protection. Unfortunately, as a group, minicars aren't performing as well as other vehicle categories."

The Mazda2, Kia Rio, Toyota Yaris and certain Ford Fiesta models all received "marginal" overall grades on the test, while the Mitsubishi Mirage, Nissan Versa, Toyota Prius C, Hyundai Accent, Fiat 500 and Honda Fit all earned "poor" ratings.

Results from these sub-compact cars fare much worse than vehicles sized just a little bit bigger, IIHS said. Among 17 cars evaluated in the small category, five earned "good" ratings and five more earned "acceptable."

Only introduced a year ago, the small-front overlap test has quickly become a key indicator of differences in automotive safety. IIHS introduced it as a way to replicate what happens when the front corner of a vehicle collides with a tree or utility pole at 40 miles per hour. In the real world, these sorts of accidents are more dangerous than others, in part because they bypass the front-end crush zones on most cars.

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Automakers have been rushing to make design changes to the front ends of their cars. Without a grade of acceptable or better, they cannot qualify for the IIHS' overall Top Safety Pick+ honor, given annually to the safest models on the market.

The 2014 Spark earned IIHS's second-highest honor, Top Safety Pick, last month, and its best-in-segment ranking in the small front-overlap will continue to help it stand out with safety-conscious customers.

Safety is "paramount to us, and this shows this is a vehicle you can feel safe putting your family in," said Chevy spokesperson Annalisa Bluhm. "Having IIHS rank us as a Top Safety Pick in December, and now ranking above the class, I think it just resonates how large our commitment to safety is."

Yet even the best vehicle in the class has shortcomings. It received a "marginal" grade in the structural category, though no mini car fared any better. Consumers should remember, IIHS cautioned, that the Spark still weighs less than 2,500 pounds and cannot be compared to heavier cars.

The two worst performers on the latest round of testing were the Honda Fit and Fiat 500, IIHS said. Crash-test dummies sustained injuries to both legs in those vehicles and the driver's space was "seriously compromised."

In the case of the Fit, IIHS said the dummy's head barely contacted the front airbag before sliding off and hitting the dashboard. In the Fiat 500, the driver's door opened, exposing occupants to the risk of being ejected.

"The latest results of the IIHS small overlap test confirm just how difficult it is to maintain passenger cabin integrity in a mini car," said Karl Brauer, senior analyst at Kelley Blue Book. " ... It rests with the automakers of these models to upgrade their structural integrity while maintaining the low purchase price that defines the category."

Pete Bigelow is an associate editor at AOL Autos. He can be reached via email at peter.bigelow@teamaol.com.