The reason passenger cars have gotten bigger and heavier so far can be mainly attributed to 2 reasons: (1) more room for passengers and luggage (2) safety requi

The reason passenger cars have gotten bigger and heavier so far can be mainly attributed to 2 reasons: (1) more room for passengers and luggage (2) safety requirements. I think they are both starting to hit the "diminishing returns" stage, so a little more efficiency could potentially go a long way.