Don't assume that they are less safe than the average vehicle. They are well engineered.
"If all else fails, you've got seat belts with pre-tensioners and force limiters, dual air bags, and the Magna-built "Tridion" safety cell, including the basket-handle roll cage structure. There is almost no crush space up front - that's what most cars use to absorb the impact of a frontal crash. In the Smart, the energy is transmitted right into the centre structure of the car, and through the unique seats and back into the engine compartment.
I don't know how it does it, but in European crash tests, Smart actually outscores much larger cars in the sub-compact field."
http://www.mcuniverse.com/The_Smart_Car_Comes_to_Canada.1325.0.html
Smart safety is explained here.
» Design and Safety