Why you should think twice before buying a small car

In testing by the Insurance Institute for Highway Safety, the Mini Cooper Countryman was the only one of 12 small cars tested to get the top "good " rating in the small overlap front crash test, which approximates the edge of a car hitting a tree or light pole. The Chevrolet Volt got a next-level "acceptable" rating while the Nissan Leaf scored a "poor."

In this new round of testing, the Volt outperformed the Leaf. It was the first time electric and plug-in hybrids had been subjected to a new, difficult crash test at the Insurance Institute for Highway Safety.

The Volt got an overall Top Safety Pick Plus rating from the IIHS because of strong performance in other front, side and rollover crash tests and because it offers an optional front crash prevention system. The Leaf is an all-electric car while the Volt is a plug-in hybrid, but the two often are considered by the same car shoppers.

The Institute said that 19 of the 32 small cars it has tested has earned a "good" or "acceptable" rating on the small overlap test. Its engineers said the Mazda5 was one of the worst performers in this test with the air bags failing to deploy and the driver side door unlatching.

Mazda said in a statement: "We take these results seriously, and are studying the results of these IIHS tests as we consider the design of future vehicles."

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    Jerry Edgerton, author of Car Shopping Made Easy, has been covering the car beat since Detroit companies dominated the U.S. market. The former car columnist for Money magazine and Washington correspondent for Business Week, Edgerton specializes in finding the best deals on wheels and offering advice on making your car last.