Gray, P., & Helmer, O. (1974). California futures study: Analysis of impacts of transportation planning : summary report. State of California, Business and Transportation Agency, Dept. of Transportation, Division of Transportation Planning.
توثيق أسلوب شيكاغو (الطبعة السابعة عشر)Gray, Paul, و Olaf Helmer. California Futures Study: Analysis of Impacts of Transportation Planning : Summary Report. [Sacramento]: State of California, Business and Transportation Agency, Dept. of Transportation, Division of Transportation Planning, 1974.
توثيق جمعية اللغة المعاصرة MLA (الطبعة الثامنة)Gray, Paul, و Olaf Helmer. California Futures Study: Analysis of Impacts of Transportation Planning : Summary Report. State of California, Business and Transportation Agency, Dept. of Transportation, Division of Transportation Planning, 1974.