The Fortwo, smaller than minicars, weighs about 1,800 pounds and is more than three feet shorter than the Mini Cooper, the Institute reported.

It weighs in at one-third the weight of a BMW X5.

But, "the big question … how safe is it?" Institute president Adrian Lund asked.

"Among the smallest cars, the engineers of the Smart did their homework," Lund said.

The diminutive two-seater earned top ratings for front and side crashes and acceptable ratings -- the second best rating -- for protection against rear impact whiplash, the report said.

The report said the Smart car makes up for its small "front-end crush zone," which typically absorbs crash impacts, with a restraint system that "does more of the work."

It also has "a stiff side structure and standard side airbags," the report said. In side-crash tests "injury forces recorded on the driver dummy's head, neck, torso, pelvis, and left leg all were low."

"However, the driver door unlatched during the crash," the Institute reported.