Some experts worry that the push for fuel efficiency in cars is creating lighter, smaller vehicles that fare less well in car accidents and expose drivers and passengers to greater risks of fatalities and serious personal injury. The Insurance Institute for Highway Safety (IIHS) has released a report that states that smaller cars in head-on collisions increase the risk of injuries for occupants.

The IIHS has found that fatality rates in smaller cars are twice as high as the rates in larger cars in multi-car crashes. In 2007 alone, 11 million people died in single-car vehicle accidents in sedans. That same year, 35 million people died in single-car accidents in the so-called “minicars” – cars designed to be fuel efficient and therefore smaller.

IIHS examined and compared only mid-sized sedans and mini cars with excellent safety records — the Smart Fortwo, the Honda Fit, and the Toyota Yaris. The Fortwo, Yaris, and Fit did not perform well in collisions with the mid-sized sedans and fares considerably worse in collisions than the larger cars. The results have led many experts to conclude that even the best-designed mini cars do not fare as well in collisions as even poorly designer medium-sized vehicles.

Much of the explanation may come down to physics. In a car crash, acceleration and size affect the force of the impact. In a smaller car, some claim, the smaller distance between the front of the car and the driver can mean more injuries to the torso and legs as well. Also, the smaller size of a mini car affects how much speed needs to be absorbed during the car crash. The IIHS tests found that the forces that impact the occupants of mini cars are much greater than the forces that act on passengers in medium-sized cars. In other words, the mini vehicles crush more and the occupants in these cars are more likely to sustain injuries.

In one IIHS crash test, the Fortwo and C-Class were compared, for example. The Fortwo made impact with the larger C-Class and veered 450 degrees. By the time the 450 degrees had come to a complete stop, both the steering wheel and the instrument panel were displaced right through the cockpit. The C-Class saw less damage and its gears did not displace into the passenger section of the car.

Advocates of mini cars note hat the IIHS tests are far ore rigorous than the safety standards outlined as necessary by the government. The Smart Fortwo does meet all standards required by the government and even the IIHS offered the car high marks for side-crash and front-crash safety among mini cars. According to the IIHS, the Honda Fit is the safest minicar tested. Even with that car, however, when the IIHS tested for impact with a larger car, the dummy in the fit made contact with the steering wheel through the air bag — indicating a risk of brain injury — and the IIHS concluded there was a “high risk” of leg injury in some crashes. All makers of minicars pointed out that the IIHS tests included tests for “extreme” conditions that simply do not often happen on the road. According to Toyota, the severity of the IIHS crash happens less than 0.06% of the time in frontal crashes.