south ‧ bound /ˈsaʊθbaʊnd/ BrE AmE adjective , adverb
[ Word Family: adjective : ↑ south , ↑ southerly , ↑ southern , ↑ southbound , ↑ southernmost ; adverb : ↑ south , southward(s), ↑ southbound ; noun : ↑ south , ↑ southerner ]
travelling or leading towards the south:
southbound traffic
The southbound lanes are closed.
The car was last seen traveling southbound on I-35.