The research techniques of instrumented full-scale collision experiments were applied to evaluate relative crash performances of smaller passenger vehicles colliding with larger vehicles. The larger vehicle weighed from 1.5-4 times as much as the smaller vehicle. The structure-overriding tendencies of larger vehicles in a particular collision were found to greatly influence the severity of exposure to injury for occupants of the smaller vehicle; relative strength of structures was similarly important. The crash safety of a motorist is shown to depend more on the use of adequate restraining devices than on the smallness of his car. Mismatched sizes of vehicles were crashed head-on, as well as in rear-end and intersection-type exposures. Analytical relationships of post-impact displacements as well as transducer and photographic instrumentation data are presented. Actual accident investigations were conducted which provided background preparation for this series of crash tests. Results of these investigations provide additional findings relative to the small versus larger vehicle collision injury problem.IT'S DANGEROUS TO BE ALIVE, but the alternative makes this hazard an endurable burden for most of us. Similarly, in certain respects, it's more dangerous to drive a small car than a large car, but this hazard has alternatives that have caused more than half of the population seeking new cars to decide to endure this hazard. Briefly stated, the alternative of driving oversize passenger cars for “short trip” activities represents specific compromises which this majority population appear unwilling to accept. The initial price of larger cars is higher; their greater complexity necessitates more frequent and costlier maintenance, their larger size requires more fuel, often of higher premium gasoline. Even with the advent of regular and no-lead tolerant high cubic displacement engines, the increased rate of fuel consumption to accommodate antismog gadgetry has more than offset savings on purchases of the cheaper low-octane fuel. Larger cars are hastening the termination of our dwindling oil reserves, predicted by some as a reality around the turn of the century; larger cars contribute proportionately more to a predicted air pollution disaster, should corrective measures not be accomplished in time. Parking problems increase with the size of the car; additionally, the larger car's turning radius complicates its ease of handling, and its width reduces vehicle to vehicle clearance between lanes as well as the separation from opposing traffic. And then there is the youth image and similar intangible aspects that motivate people to purchase small cars.For all the smaller car advantages, almost half of the United States population still select large cars; however, on the basis of related observations, the probability is that safety is not foremost among the factors governing a decision to buy big. Habit pattern still accounts for many such purchases, as does prestige, need to accommodate a larger family, or for carrying bulky equipment. Unquestionably, these factors compete to displace safety to a lower priority of consideration.In this paper, the safety aspects of size will be shown to depend significantly on whether or not restraining devices are used by the small car motorist impacting a larger vehicle and that for some collision exposures, vehicle size has no bearing on injury exposure. Additionally, certain safety advantages of a small car are inherent in its design, such as maneuverability, increased roof crush resistance, absence of power-assist steering, and brake failures, all tending to make an alternative to the purchase of a large car an acceptable decision.