Safety and Systems Analysis, with Applications to Traffic Safety

Abstract

Much that goes on in the world today is described in terms of systems. There seems to be increasing recognition of the fact that very little of the more important kinds of human activity takes place in isolation; so interconnected and interdependent have these activities become that it is standard practice today to look beyond the immediate inputs and outputs of these activities and to ask about their consequences for the rest of the system. We therefore speak of our educational system, our defense systems, medical care system, transportation system, and economic systems as groupings of related activities. We ask ourselves about the goals of these systems and the resources available for operating them. We design these systems to yield us a maximum of whatever objective we have set for them in exchange for the resources we have committed to them. The scale of concern of the systems analyst and designer varies over a wide range, from the trivially small to the globally large. A military systems analyst may define his area of concern as the defense of naval task forces against submarine attack and thus focus his attention on a limited system containing only submarines, surface and air forces, undersea detection devices, and weapons appropriate to the tactical encounter between offensive submarines and defensive task forces. Another analyst, concerned with the broader objective of defense of the coastal regions of the continental United States, would have a larger system to consider-one containing the complete catalog of detection devices and weapons systems needed to counter the various forms of subsurface, surface, and airborne attack that could be launched. Whatever his scale of concern, the designer has the task of producing a system possessing a high degree of effectiveness. For a transportation system, which may consist of the network of roads connecting a group of cities, the measure of effectiveness is generally considered to be the cost per ton of cargo or per passenger moved in this network. The systems designer, accordingly, lays out roads, sets traffic controls, and in general arranges facilities and services which yield as low a cost per unit of transportation as possible. Submerged in the details of design considerations and generally not given explicit recognition is the question of safety. The unstated constraint on the quest for economical and efficient transportation is a requirement that the planned movement