Transportation Planning 70 Environmental aspects 56 Transportation and state 42 Data processing 39 Automation 24 Mathematical models 24 Transportation engineering 23 Social aspects 21 Management 20 Design and construction 18 Roads 18 Traffic engineering 17 Research 16 Technological innovations 16 Safety measures 15 Local transit 14 Urban transportation 14 Electronics in transportation 13 Land use 13 Hazardous substances 12 Mobile communication systems 12 Pollution 12 Sustainable development 12 Intelligent Vehicle Highway Systems 10 People with disabilities 10 System design 10 Telecommunication 10 Administrative 9 Automobiles 9