Westbound means travelling towards where the sun sets. The westbound carriageway, a westbound train, westbound traffic.
It is the standard word on road signs, timetables and traffic reports, where naming the direction is quicker than naming the destination. Westbound flights across the Atlantic take longer than eastbound ones, because the jet stream blows the other way. Note the -bound ending, meaning headed for, which is unrelated to tying.
1adjectivewestboundTravelling towards the west.
“Westbound traffic on the motorway was held up for hours after the accident.”
westbound is a direction of travel.
Proto-Indo-European
*wek⁽ʷ⁾speros
Middle English
west
English
west
English, today
westbound
From west + -bound. west comes from Middle English west. From Middle English west, from Old English west, from Proto-West Germanic westr (“western”), from Proto-Germanic westrą (“west”), from Proto-Germanic westraz (“west”), from Proto-Indo-European wek⁽ʷ⁾speros (“evening”). 2
Etymology from Wiktionary, CC BY-SA