Security strategies must relate to the systems to be secured and defended. Transportation systems’ common characteristics include the following:
Openness and accessibility. Designed and organized for the efficient, convenient, and expeditious movement of large volumes of people and goods, transportation systems must have a high degree of user access. In some cases—highways, for example—access is almost entirely open. Many transportation facilities, such as train stations, are public places, open by necessity. In other cases, access is more limited, as in commercial aviation—but still not fully closed. Even in the case of the latter, it is notable that access to most airport lobbies, ticket lines, and baggage check-in areas remains unrestricted. Moreover, much of the transportation infrastructure, from airports to highway and rail bridges, was designed and built long before concerns over security and terrorism. Fully integrating security will take many decades, as assets are gradually modified and replaced.
Extent and ubiquity. Transportation systems require vast amounts of physical infrastructure and assets.3 The U.S. highway system consists of 4 million interconnected miles of paved roadway, including more than 45,000 miles of interstate freeway and 600,000 bridges. The freight rail networks extend for more than 300,000 miles, and commuter and urban rail systems cover some 10,000 miles. Even the more contained civil aviation system has some 500 commercial-service airports and another 14,000 smaller general aviation airports scattered across the country. These networks also contain many other fixed facilities such as terminals, navigation aids, switchyards, locks, maintenance bases, and operation control centers.
Most of this infrastructure is unguarded and sometimes unattended. Distributed over the networks are millions of vehicles and containers, which are repeatedly moved from one location to another, complicating the task of monitoring, safeguarding, and controlling them.
Emphasis on efficiency and competitiveness. Although much of the transportation infrastructure in the United States is owned by the public sector, the development of this infrastructure is driven largely by the demands of private users. Widespread use of private cars and motor carriers, for instance, spurred greater investment in the highway system relative to public transportation and railroads. Likewise, travel by motor vehicle and airliners displaced demand for intercity passenger rail service in the second half of the 20th century, prompting increased government spending on airports and freeways. The economic deregu-