<Tr> <Td> Grayson </Td> <Td> Low Gap </Td> <Th> 215.7 </Th> <Td> 347.1 </Td> <Td_colspan="1"> SR 89--Mt . Airy, Galax </Td> <Td> One - quadrant interchange </Td> </Tr> <Tr> <Td> North Carolina </Td> <Td> Alleghany </Td> <Td> ​ </Td> <Th> 217.2 </Th> <Td> 349.5 </Td> <Td_colspan="1"> NC 18--Sparta, Mt . Airy </Td> <Td> One - quadrant interchange </Td> </Tr> <Tr> <Td> ​ </Td> <Th> 229.6 </Th> <Td> 369.5 </Td> <Td_colspan="1"> US 21--Roaring Gap, Sparta </Td> <Td> Two - quadrant interchange </Td> </Tr> <Tr> <Td> ​ </Td> <Th> 248.0 </Th> <Td> 399.1 </Td> <Td_colspan="1"> NC 18--North Wilkesboro, Laurel Springs </Td> <Td> One - quadrant interchange </Td> </Tr>

Where does the blue ridge parkway start and finish