All things being equal, this is generally a little bit true, even for collisions with rigid, fixed obstacles - but vehicle design is critical here. For instance, a cab forward truck with no real crumple space does not benefit from mass, as the deformation of the pax compartment is the primary concern. A very lightweight vehicle that is very deformable and has a long crumple zone might outperform a heavier vehicle in terms of the acceleration imparted to the passengers.
The problem is that a “fixed” solid object has effectively infinite mass. This applies when the collision displacement of the obstacle can be measured in fractions of a millimeter. In these cases, the ratio of the lightweight vehicle to the effective mass of the obstacle is effectively the same as with the heavier vehicle vs the obstacle. Here, mass pays no dividends. Only the distance / time covered during the sudden deceleration, and the integrity of the passenger compartment. Of course, the efficiency and extent of restraint systems will also play a major role. But it’s not an automatic win for heavier vehicles in this case.
Notably, most collisions are not with immovable objects, but with other vehicles. In that case, mass is going to win almost every time, since the acceleration experienced by a subcompact vs a full sized SUV is about 2x, which means the forces imparted on the passengers in terms of static loads on their bodies and bones will be 4x.
For passenger survivability in most accidents, the incentives fall heavily towards using the heaviest well constructed vehicle that you can afford.
The problem is that a “fixed” solid object has effectively infinite mass. This applies when the collision displacement of the obstacle can be measured in fractions of a millimeter. In these cases, the ratio of the lightweight vehicle to the effective mass of the obstacle is effectively the same as with the heavier vehicle vs the obstacle. Here, mass pays no dividends. Only the distance / time covered during the sudden deceleration, and the integrity of the passenger compartment. Of course, the efficiency and extent of restraint systems will also play a major role. But it’s not an automatic win for heavier vehicles in this case.
Notably, most collisions are not with immovable objects, but with other vehicles. In that case, mass is going to win almost every time, since the acceleration experienced by a subcompact vs a full sized SUV is about 2x, which means the forces imparted on the passengers in terms of static loads on their bodies and bones will be 4x.
For passenger survivability in most accidents, the incentives fall heavily towards using the heaviest well constructed vehicle that you can afford.