Transportation History 124 Transportation and state 90 Law and legislation 83 Railroads 66 Finance 63 Planning 57 more ... Environmental aspects 52 Security measures 43 Hazardous substances 41 Social aspects 40 Roads 38 Infrastructure (Economics) 37 Safety measures 37 Local transit 36 Federal aid to transportation 35 Prevention 33 Terrorism 26 Armed Forces 23 Transportation engineering 23 Economic conditions 22 Government policy 22 World War, 1939-1945 22 Research 21 Management 20 Transportation Economics 20 Economic aspects 19 Transport 19 Transportation, Automotive 19 Safety regulations 17 less ...