The phrase "southbound lanes" refers to the section of a road or highway that is specifically designated for vehicles traveling in the southern direction. Full definition
A structural inspection was performed on the damaged span before it was partially reopened around 5:15 p.m.. All but one southbound lane from Rockland to Westchester was expected to be open by Wednesday morning. (nypost.com)
It landed on top of a 2001 Ford Expedition, narrowly missed a police officer, and shut down North Atlantic's southbound lanes for three hours, police said. (articles.orlandosentinel.com)
Motorists are advised that the right southbound lane will remain closed until repairs are completed. (hudsonvalleynewsnetwork.com)