er- standing the different types of access to networks. These types of access have generated a variety of public policy actions. Classifying the types of access provides insights into inconsistencies in public policies that can create economic inefficien- cies. Our classification scheme provides the basis for the development of a new Coasian theory of communications networks. The boundaries of the private net- works, and their pattern of interconnections, depend on a comparison of the costs of governing networks by firms and the transaction costs of interconnecting net- works. Markets can be expected to generate efficiencies in the structure of private networks and the pattern of interconnections between networks. A. Types of Networks There are many types of networks. The focus of our policy discussion is on commu- nication networks. However, many of our conclusions apply to regulation of some Networks in Telecommunications Table 1.1. Value added by industry as a percentage of Gross Domestic Product as of 2006 Utilities Wholesale trade Transportation and warehousing Air transportation Rail transportation Water transportation Truck transportation Transit and ground passenger transportation Pipeline transportation Other transportation and support activities Warehousing and storage Information Broadcasting and telecommunications Total 13.4% Source: U.S. Department of Commerce (2008, Table 2). types of transportation and distribution networks. For completeness, we touch briefly in this section on social and business networks, although these are beyond the scope of our later discussion. 1. Communications, Transportation, and Distribution Networks The contributions of the transportation and distribution network industries to the U.S. gross domestic product (GDP) are summarized in Table 1.1. Network indus- tries are primarily located within the Transportation and Public Utilities sector and constitute more than 13 percent of GDP. There are three parts to this sector: trans- portation, communications, and utilities other