identifying the unique role of the U.S. Department of Transportation (DOT) is a key challenge.

Now that the Cold War is over, security concerns in many fields are being focused increasingly on the threat of terrorism, whether by an organized state or state-sponsored group as a form of "asymmetrical warfare" or by a nonstate group or individual motivated by extremist ideology or hatred. The present study is just one of many recent and continuing efforts to address this problem, either in broad terms or with a specific focus on individual sectors of the nation's infrastructure.

The goal of this chapter is to provide an overview of these issues as background for the remainder of the report. The chapter concludes with a brief description of the general structure and approach of the report.

The U.S. surface transportation system is large, complex, and decentralized. DOT, despite its regulatory and other responsibilities for transportation, actually