One argument presented against buying an SUV is consideration for the safety of passengers in other lighter cars. In an impact between a heavy car and a light car, the light car loses. One must also consider the possibility of collision with a larger car. The dilemma is, does one buy the lightest car possible to lessen the threat to others or buy a heavier car to lessen potential injury to passengers? Some would suggest that we let the government solve the problem by specifying that we all drive the same vehicles, designed for mutually assured equivalent injury (MAEI). Let's take a lighthearted look at the design implications of MAEI.
In control theory, the performance function (PF) measures how well a particular design satisfies the design requirements. The ideal design optimizes the PF within constraints. One PF based solely on MAEI is the absolute value of the difference in the physical trauma (T1 & T2) suffered by the occupants of two cars in a collision, i.e. PF = "T1-T2" Consider the implications of designing to minimize this PF.
The ideal design is achieved if T1 = T2. This exposes a flaw in the philosophical basis for the PF since it does not consider the amount of trauma. The PF would be minimized either by killing everyone in both vehicles, or by having no injury. A more reasonable PF would include a factor related to the total amount of trauma. For example, PF = "T1-T2" + T1+T2. Now the optimal designisT1=T2=0.
In an attempt toachieveT1=T2=0, there could be ejection seats so that passengers do not experience the deceleration of the vehicles. There would have to be compensation for the relative speeds of the cars so that all parachutes have the same velocity (non-intersecting trajectories) and attain the same heights. Another option would be to have a universal speed limit lower than the threshold for injury, perhaps 20 mph with innovative design.
Without ejection, we must have the safest (tank like?) cars possible. These may be pollution generating gas-guzzlers, but these factors aren't in the PF. Generally as we add new factors to the PF we reduce the MAEI performance. Safe cars will be expensive, so the government will have to provide them, raising our taxes. No trucks could be allowed on the highways with cars. Trucks could have their own highways or travel at night with cars traveling in daytime.
T1=T2 requires that we all drive identical cars. The possibility of front to rear collisions implies that the rear of the car must be the same as the front, requiring big arrows painted on the side so we can tell which direction they are going. Side impacts require structures that are the same in every direction horizontally (cylindrically shaped). You see where this is going —spherically shaped homogeneous vehicles. The loaded weight of every vehicle would have to be the same. If your car were over or under weight, you would have to remove or add ballast. As you burn gasoline you would have to add ballast from a breakaway compartment. All passengers must have the same automatic restraints that assure the same level of injury regardless of angle of impact.
This could clearly be carried on endlessly of course, but aside from the humor, there are serious issues here. It is obvious that the PF of life should include numerous factors. Among those factors are personal freedom and responsibility. As we reflect on the willingness of our astronauts and military personnel to lay their lives on the line for the sake of higher causes, we realize that there are values more precious than safety. Freedom is almost always obtained at the expense of safety, and requires an assumption of personal responsibility. Responsibility for the consequences of our choices gives us dignity in spite of our imperfections.