Subways 21 Local transit 8 Urban transportation 5 Commuting traffic 4 Railroads 4 Construction 3 Gay people 3 more ... History 3 Railroads, Elevated 3 Roads 3 Streets 3 Transit systems 3 Transportation 3 Bridges 2 Design and construction 2 Railroad employees 2 Street railroad stations 2 Street railroads 2 Cars 1 Crime 1 Crowds 1 Docks 1 Ferries 1 Piers 1 Piers & wharves 1 Power plants 1 Railroad engineeriung 1 Railroad passenger cars 1 Research 1 Rolling stock 1 Sewerage 1 Statistics 1 Street-railroads 1 Subway 1 Subway stations 1 Tunnels 1 Urbanization 1 Walls 1 less ...