The "smart" was due to be released in Europe shortly after the Mercedes A-Class failed the infamous Swedish 'Elk Avoidance Test' so M-B tested the Smart to see if it would pass - it didn't.
They delayed the release and made numerous engineering changes to make it super-safe including the addition of the latest Electronic Stability Control, Anti-Lock Braking and Brake assist, from the S-Class. They also increased the track by fitting wider wheels & tires at the back. The car is designed around a "Tridon" safety cage (essentialy a built-in roll cage) and front and side air-bags are standard.
Despite its size, the Smart Car is probably as safe dynamically and passively as any other mercedes, although I still wouldn't want to be hit by an 18-wheeler in one
Mind you, I wouldn't want to be hit in my W126 by a truck either, I'm sure the SDL won't bounce off as well as a Smart.
