Transportation agencies around the world continue to face fiscal challenges caused by the growing gap between the costs of preserving and expanding highway infrastructure and available highway program funding. The lack of dedicated public funding sources for transportation (in most other countries high motor fuel taxes are generally used non-transportation social programs) and the burdens placed on current transportation infrastructure (both highway and rail) by a growing global economy has long prompted transportation policymakers overseas, especially in Western Europe, to develop and apply alternative ways to finance and deliver needed transportation infrastructure. A number of countries have turned to the private sector for relief in the form of contractual Public-Private Partnerships (PPPs), representing a wide variety of project financing and delivery approaches to access capital markets; implement new technology; and expedite project delivery, operations, and maintenance in a more cost-effective manner. The common element of a PPP is that the public sponsor of infrastructure projects engages the private sector to a greater degree in the performance of certain functions previously handled by the public sector. This can range from contracted maintenance services to full financing, development, operations, and preservation. Some countries have effectively turned over the responsibilities, risks, and rewards associated with performing these functions to private sector through long-term concessions or franchises, whose financing is supported by tolls, shadow tolls, or availability payments (a form of shadow tolls).