Train Unit (Rolling Stock) : Vehicle
    weight = double
    max_speed = double
    braking_force = double
    friction_force = double
    air_resistance = double
    joint_distance = double
    connection_distance = double
    energy_per_hit_point = double
    rail_category = string ?
    drive_over_tie_trigger = TriggerEffect
    tie_distance = d(1)
    back_light = Light
    stand_by_light = Light

    
    constant (hard coded) min distance between joint and BoundingBox edge = double(0.2)
      /** Used when searching neighbour to be connected, to avoid, moving to the other side (inner) of the joint.
       *  ╔════════════╗
       *  ║  *------*  ║
       *  ╚════════════╝
       *  <------------> Bounding box
       *     <------>    Joints
       *  <->       <->  x > min distance between joint and BoundingBox edge */
