They operate as a sub-route of the parent route and there can be more than one SWT per trunk route.
From the en.wikipedia.org
Akoray cooperated with the Mughals to safeguard the trunk route and was generously rewarded for his assistance.
From the en.wikipedia.org
The northern section of the Oxford Canal between Coventry, Braunston and Napton remained an important trunk route, and remained extremely busy with freight traffic until the 1960s.
From the en.wikipedia.org
The WCML was not originally conceived as a single trunk route, but was a number of separate lines built by different companies between the 1830s and the 1880s.
From the en.wikipedia.org
How about throwing a pair of sneakers in the trunk and stopping at a park en route to or from work?
From the delawareonline.com
I watch in goggle-eyed disbelief as we sail past the exit to the M1, the main trunk road north of London and head straight into the busy orbital route around town.
From the economist.com
Littlehampton is connected to the A27 south coast trunk road by the A284, which also provides the main north-south route out of the town and links to the A29 and A24.
From the en.wikipedia.org
The route forms a key artery on the eastern side of Great Britain and is broadly paralleled by the A1 trunk road.
From the en.wikipedia.org
The A617 primary route passes 2 miles to the north of the town in Hockerton, and the A1 and A46 trunk routes are both 7 miles away in Newark.