During the last few decades, federal legislation has increasingly facilitated use of PPPs through relevant guidelines for federal funds and federal-aid highways. Federal legislation passed in 1991 first allowed federal funds to be mixed with private funds for highway development and construction. It also authorized states to use federal highway funds on any toll road owned by a public entity and on approved private facilities, excluding construction of new toll roads on the Interstate system.88 In the 2005 federal transportation bill (SAFETEA-LU), Congress eliminated dollar thresholds on design-build contracting, making any federal-aid highway project potentially eligible to use this approach.89