The high-profile asset monetization lease contracts executed on the Chicago Skyway in 2005 and the Indiana Toll Road in 2006 are but one way the private sector can take a greater than usual interest in transportation infrastructure development, operations, and maintenance. There are many other varieties of PPPs, and any discussion of the merits of PPPs needs to be clear on what is being discussed. This section provides an overview of the many types of PPPs that have been implemented or considered in North America.