Yes, a larger
car will be better off if involved in a crash than a smaller one. But if in a crash, it is a 50% chance it won't be with another car. In a single car crash, the heavier car's weight equals higher forces involved on the car and the occupants. Going the same speed, the twice as heavy car will experience twice the force when hitting a tree than the lighter one. Any extra reinforcing and crumple zone space it may have is needed to absorb the extra force.
The ideal design for a crash will have the car crumple up like a tin can while leaving the cabin space intact. In slow mo footage of a smart car crash test, you can see the force from the front crash get channeled around the cabin and damage the car's rear.
Trucks and SUVs have historically had less stringent safety regulations on them than cars. Their higher center of gravity also means a higher chance of roll over.
"Forty-five percent of car occupant deaths in 2012 occurred in single-vehicle crashes and 55 percent occurred in multiple-vehicle crashes. In contrast, single-vehicle crashes accounted for 65 percent of SUV occupant deaths and 65 percent of pickup occupant deaths." IIHS, 2012
So regardless of the car's size, you are more likely to die in a pick up hitting a tree than a small car.
"Historically, the rates of driver deaths per million registered vehicles have been higher for the smaller and lighter vehicles. This was true again in 2012, but the differences were less extreme than they used to be."-IIHS
Improving safety regulations and technology is covering the gap in deaths between car sizes. But we are already talking about tiny numbers to begin with. The number of fatalities for mid-size cars is 33, 49 for small, and 77 for mini
per million registered vehicles. Your chance of dying in year, as an individual, is under a thousandth of a percent no matter you are driving.
While the IIHS has the graph with the about numbers, defines their vehicle sizes, and states small cars are less safe in the introductory paragraph, they do no other break out of the data by car size. Being cheaper, a small car is morelikely to be the the first new car of a younger person who doesn't make as much a more mature person. The under 30 makes up a larger percentage of fatalities than the others. We also don't know of many of the small car deaths involved just itself or multiple heavier vehicles.
http://www.iihs.org/iihs/topics/t/ge...enger-vehicles