What consumers should know about passenger cars and safety

By Joe Wiesenfelder, Cars.Com  |  July 29, 2007

As a class, cars have a few advantages over light trucks, and a few disadvantages. As is the case in any body style, it's easier to judge the crashworthiness of better-selling models because they're more often crash tested. Because wagons tend to be low-volume cars, their crash performance isn't quite as clear.

As a class, cars' and wagons' main advantages over light trucks are their lower center of gravity, their size and their braking. Their lower center of gravity translates to a lower likelihood of rollover. While a car that goes off the pavement can roll, its lower center of gravity makes it less likely to do so than pickup trucks or SUVs, which are more easily "tripped" by a curb or soft shoulder. Cars' lower center of gravity also makes them more nimble and capable of avoiding a collision, as do their smaller size and typically shorter braking distances.

Unfortunately, a couple of passenger car advantages are also disadvantages: The lesser weight and lower height make them vulnerable to heavier, higher vehicles. Historically, pickups and truck-based SUVs have not been as meticulously designed to absorb crash energy, but their weight and height make up for it in crashes with lighter vehicles, whose occupants pay the price.

Aside from the weight issue, it's a matter of compatibility: A high truck can ride up over the most robust part of a car's frame structure, bypassing its crumple zone and plowing into its cabin.

There's evidence that SUVs are becoming less deadly to occupants of cars with which they collide. Many manufacturers have worked since 2003 to make SUVs more compatible in crashes with smaller vehicles by lowering their frames to engage a car's crumple zones. The Insurance Institute for Highway Safety cross-referenced a list of such SUVs with fatality data from the past few years and found that the fatality risk for a belted car driver was 18 to 21 percent lower when crashing head-on with a compatible SUV than with a conventional one. (There's practically no change for unbelted drivers.) The side-impact results are more dramatic: a 47 to 49 percent decrease in car-occupant fatality risk when hit by a compliant SUV.

Automakers haven't come as far in making cars more compliant. Honda is addressing the compatibility issue with Advanced Compatibility Engineering, which designs a car's structure to engage a higher vehicle -- not leaving this responsibility to the opposing truck's design. ACE seems to be paying off. At the start of the 2007 model year, the Honda Civic is the top-scoring small car in Insurance Institute for Highway Safety crash tests.

Buyers who are concerned about compatibility and see no high-rated cars they desire should consider a higher-riding car or crossover vehicle, which increases the chance of compatibility in a crash.

A side impact from a truck or SUV is perhaps the greatest danger. There are just inches and practically no steel between a truck bumper and a car occupant's upper body. This is why side-impact airbags are a must. Features can't compensate for weight and height differences, but they can certainly help.