Northbound means travelling towards the north. The northbound carriageway, a northbound train, northbound traffic.
It is the standard word on signs and in traffic reports. In spring migration in the northern hemisphere it is the direction of travel, and radar can now watch the whole northbound movement of birds across a continent. Note the -bound ending, meaning headed for.
1adjectivenorthboundTravelling towards the north.
“The northbound lanes of the motorway were closed after the accident.”
northbound is a direction of travel.
Middle English
north
English
north
English, today
northbound
From north + -bound. north comes from Middle English north. From Middle English north, from Old English norþ, from Proto-West Germanic norþr, from Proto-Germanic nurþrą, ultimately from Proto-Indo-European nér (“below (the surface)”). The meaning developed either from "region where the sun is below (the earth)" or from "left side of someone who turns to the east when praying". 2
Etymology from Wiktionary, CC BY-SA