As we have started telling more people about the pregnancy, I'm being told, I "need a safer car". I drive a 2012 Ford Focus Hatchback, a couple of people are trying to tell me I need something bigger and safer. I just reply back that the safest feature of any car is the person sitting behind the steering wheel.
*sigh*. Misconceptions. Bigger does not equal safer in all situations. Basically, your change in momentum is going to be proportional to the force experienced.
Yes, it's true a bigger car is better in a collision with another car.
Assuming the cars are going at equal speeds, the heavier car is going to push back the smaller car, meaning the smaller car has a much higher change in momentum (velocity went from positive to negative) than the bigger car (velocity went from positive to zero).
But a smaller car is better in a collision with another (unmoveable or approximately unmoveable) object. Both the big and small cars will experience the same change in velocity, but momentum is mass * velocity. Hence, the bigger car will experience a larger change in momentum and a larger force.
Then the question becomes, well what is more likely? A collision with another car or a collision with another object? That I don't know the answer to.
However, regardless of which type of accident is more likely, knowing that doesn't really help you that much, simply because a car accident is thankfully a rare enough event that you won't be able to apply the law of large numbers and actually realize the long term probabilities of car accident rates b/w other cars and other objects.
So I say screw the whole big vs small car for safety debate. Just buy a car according to your needs. If it happens to be a big car, that's great. If it's a small car, that's great too.