southbound       
adjective, adverb uk/ˈsaʊθ.baʊnd/ us/ˈsaʊθ.baʊnd/
 南行(的);向南(的)
going or leading towards the south
  southbound passengers/traffic 南行乘客/车辆 
 Traffic is bad on the M6 southbound, after junction 11. M6高速公路南行段在11号出口后拥堵。 
 Traffic is bad on the 405 freeway.  405号高速公路上发生拥堵。 
 Compare: southward adjective