<Tr> <Td> 5 . </Td> <Td> Bay Area Rapid Transit (BART) </Td> <Td> Bay Area Rapid Transit District </Td> <Td> San Francisco Bay Area </Td> <Td> 135,310,700 </Td> <Td> 446,200 </Td> <Td> 7005180246528000000 ♠ 112 miles (180 km) </Td> <Td> 4,290 </Td> <Td> 1972 </Td> <Td> 46 </Td> <Td> </Td> </Tr> <Tr> <Td> 6 . </Td> <Td> SEPTA (Broad Street, Market--Frankford, and Norristown High Speed Lines) </Td> <Td> Southeastern Pennsylvania Transportation Authority </Td> <Td> Philadelphia </Td> <Td> 94,209,100 </Td> <Td> 311,800 </Td> <Td> 7004590629248000000 ♠ 36.7 miles (59.1 km) </Td> <Td> 8,496 </Td> <Td> 1907 </Td> <Td> 75 </Td> <Td> </Td> </Tr> <Tr> <Td> 7 . </Td> <Td> Port Authority Trans - Hudson (PATH) </Td> <Td> Port Authority of New York and New Jersey </Td> <Td> Manhattan; Hudson County, and Newark </Td> <Td> 78,553,600 </Td> <Td> 270,900 </Td> <Td> 7004222089472000000 ♠ 13.8 miles (22.2 km) </Td> <Td> 19,630 </Td> <Td> 1908 </Td> <Td> 13 </Td> <Td> </Td> </Tr> <Tr> <Td> 8 . </Td> <Td> MARTA rail system </Td> <Td> Metropolitan Atlanta Rapid Transit Authority </Td> <Td> Atlanta </Td> <Td> 68,678,700 </Td> <Td> 213,800 </Td> <Td> 7004766047744000000 ♠ 47.6 miles (76.6 km) </Td> <Td> 4,492 </Td> <Td> 1979 </Td> <Td> 38 </Td> <Td> </Td> </Tr>

How many subway systems are there in the us