This is a tutorial of how to do it.

https://www.youtube.com/watch?v=MCNvczYQbMs

Special thanks to The_Gaming_4

Config.json file:

{

"Trains": [
{
"VehicleID": (vehicle ID),
"RoadIndex": (index)
},
{
"VehicleID": (vehicle ID),
"RoadIndex": (index)
}
]
}