411 REFERENCE · Wikibooks
Trainz/Changing the default cars on roads
Reference material by Wikibooks contributors. This retains its source identity and is not 411 news reporting.
You may need to change the region but you can add specific cars or trucks if you know their kuid number by modifying the layout or route's config.txt.
An example is:
region <kuid:-1:7803>
carrate 20
car0 <kuid:329364:1501>
car1 <kuid:329364:1165>