Vehicle fleet downsizing has been discussed in Europe as an aspect to reduce fuel emissions. A recently developed mathematical model was used to study the individual effects of fleet mass distribution, impact speed reductions and inherent vehicle protection on average injury and fatality rates for downsized fleets. A baseline fleet of 700-2000 kg was downsized by a) reducing all vehicle masses by 10% or 20% and b) by removing all cars heavier than 1400 or 1200 kg.The results showed that the safety can be maintained if the vehicle masses are reduced proportionally to their original mass. A higher safety level can be achieved by removing the heavier vehicles. Traffic safety can be further enhanced by impact speed reductions or by improvements of restraint systems and vehicle compatibility. The safety level would rise more by implementation of radar-activated brakes or controlling city speed limits than by intensified highway patrols, to eliminate crashes with impact speeds over 140 mph or with an average velocity change of 70 mph. However, a maximum impact speed at 100 mph would reduce the number of fatalities more effectively than a small reduction in all impact speeds.It was concluded that a downsized fleet can result in fewer fatalities, depending on the downsizing strategy. Furthermore, the model can be used to estimate the effects of potential safety strategies.