Units: vehicles, or whole trains (locomotive plus params.wagons wagons).
OptionallaneMetres to the right of a path (roads use their own lanes).
OptionalparamsType parameters (see VEHICLE_KINDS).
Route.
OptionalspeedCruise speed range, m/s. Default depends on the type.
OptionaltintPaint every unit this colour (#rrggbb) instead of picking from the model's palette.
Vehicle type.
OptionalvariantsDistinct generated models the units cycle through (more = more variety, more draw calls). Default 4.
One group of vehicles of one type sharing a route. Plain JSON.