The 2008 Smart Fortwo received the highest rating for front-end and side-impact testing conducted by the U.S. Insurance Institute for Highway Safety, judged against vehicles of similar size and weight. (Insurance Institute for Highway Safety/Associated Press)

The 2008 Smart fortwo micro car, the smallest car for sale in the U.S. market, has earned top scores in crash tests conducted by the U.S. insurance industry.

The 2½-metre vehicle received the highest rating of "good" in front-end and side-impact testing by the U.S. Insurance Institute for Highway Safety, helping address some concerns that consumers may be more vulnerable in the tiny two-seater.

The tests, released Wednesday, show how well vehicles stack up against others of similar size and weight. The institute noted that the front-end test scores can't be compared across weight classes, meaning a small car that earns a good rating isn't considered safer than a large car that did not earn the highest rating.

Adrian Lund, the institute's president, said a small car may be more practical in congested urban areas where serious, high-speed crashes are less likely. The institute conducted the crash test to help guide consumers who want a small car that can give them good protection.

"All things being equal in safety, bigger and heavier is always better. But among the smallest cars, the engineers of the Smart did their homework and designed a high level of safety into a very small package," Lund said.

The institute's frontal crash test simulates a 65 km/h crash with a similar vehicle. The side crash simulates what would happen if the vehicle was struck in the side by a sport utility vehicle at 50 km/h.

In a test that assessed the vehicle's protection in rear crashes, the fortwo received the second-highest rating of "acceptable."

The vehicle, which had sold 6,159 units in the U.S. through the end of April, has a fuel consumption of 7.0 L/100 km in the city and 5.7 L/100 km on the highway. The fortwo is more than one metre shorter and about 300 kilograms lighter than a Mini Cooper.

In earlier crash tests conducted by the U.S. government, Smart received the top score of five stars in side testing but the driver door unlatched during the test and opened. While it did not affect the vehicle's test score, government regulators said the incident required them to note a safety concern for the vehicle which will appear on window stickers at dealerships.

The concern was warranted because the unlatching of the door could increase the likelihood of a driver or passenger being ejected from the vehicle, the U.S. National Highway Traffic Safety Administration said.

When the IIHS conducted its side test, the driver door also became unlatched. But the institute said the injury measurements on the test dummy were low and the opening didn't affect the dummy's movement.