Although federal law prohibits the conversion of existing free interstate highway facilities to toll roads, state highways are exempt from this law. The presence of legislation enabling such conversions of state highways indicates that the government is interested in using PPPs not only to finance construction contracts (green fields projects), but standalone maintenance and operation contracts (brown fields projects) as well. While we often find discussion to mix adoption of tolls and PPPs, these two issues are fundamentally separate, as there is no strong link between financing and the organization of infrastructure provision (OECD 2008). Thus, it is not necessary to relate an application of tolls to PPP legislation.
Apart from PPPs, an application of tolls should be considered for any facility where it increases the efficiency to the use, finance, maintenance, and management of existing facilities while it does not cause significant adverse effects on equity. Five states have restrictions on converting existing roads to tollways, with six others silent on the matter. Colorado, for example, allows only for existing HOV lanes to be converted into HOT lanes. Although allowing for existing fee-free roads to be converted into toll roads can be very unpopular with users, it can increase the efficiency of the use and also provides more flexibility to public agencies when crafting PPP agreements. In June 2007, Texas restricted the ability of public agencies to convert free roads to tolled roads as part of an anti-privatization bill (Barlas 2007). In the long run, however, it is a better idea to allow for these conversions and provide the public with a way to comment on such proposals, in addition to a careful analysis of economic efficiency in these projects.