Fetching details from the dictionary...

main line; trunk line
幹線道路は朝の通勤時間帯に特に混雑する。
Main roads are especially congested during the morning commute.
新幹線は日本の鉄道幹線として重要な役割を担う。
The Shinkansen plays an important role as Japan's main railway line.
幹線から外れた地域は交通の便が悪いことが多い。
Areas away from main routes often have poor transportation access.