1. Agrawal , A.W. H. Nixon A. Hooper 2016 Public Perception of Mileage-Based User Fees, NCHRP Washington DC Transportation Research Board http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_syn_487.pdf
2. American Association of State Highway and Transportation Officials (AASHTO) 2015a State Transportation Funding Proposals as of June 8 2015 Washington, DC AASHTO http://www.transportation-finance.org/pdf/featured_documents/state%20transportation%20funding%20proposals%202015-6-8.pdf