These are vehicle add-on parts from the Dura-Built parts thread. 
Archived link: https://web.archive.org/web/20151114104033/http://www.rigsofrods.com/threads/86543-Dura-Built-Vehicle-Add-on-Parts

Part credits:

DODGE charger (now Charger)
DarthCain
Mitchieboy®
CarBoy
Silvermanblue
JAW-4 (now MrSteakPotato)
Excisionized
RORLover563 (now Kitty)
Logger95
Dereksh97
Bj118
GamerN3x


Converted to new addonpart format by CuriousMike.