Cost of operation Transportation 10 Costs 8 Transportation, Automotive 8 Economic aspects 4 Hospitals 4 Motor vehicles 4 Railroads 4 Trucking 4 Trucks 4 Automobiles 3 Mathematical models 3 Roads 3 Agricultural machinery 2 Airlines 2 Data processing 2 Evaluation 2 Maintenance and repair 2 Research 2 Taxation 2 Agriculture 1 Airplanes 1 Appropriations and expenditures 1 Auditing 1 Bibliography 1 Building management 1 Buildings 1 Chemical plants 1 Congresses 1 Construction industry 1