Express highways 81 Roads 17 Economic aspects 12 Environmental aspects 7 Design 4 Highway planning 4 Interchanges and intersections 4 Planning 4 Social aspects 4 Finance 3 Public opinion 3 Regional planning 3 Traffic engineering 3 Transportation 3 Communication systems 2 Design and construction 2 Electronic traffic controls 2 Environmental impact statements 2 Highway engineering 2 Highway research 2 Local transit 2 Traffic surveys 2 Accounting 1 Airspace utilization 1 Appropriations and expenditures 1 Beltways 1 Bridges 1 Budget 1 Buildings, structures, etc 1 Business relocation 1