Ben

The traveler only receives the benefit of the train’s forward movement when he and the train are in physical contact. Consider sitting in a seat on a stationary vehicle when the vehicle starts its forward movement you are pressed back into the seat. Of course the greater the acceleration the more you are “pressed back” into the seat. This pressed back into the seat is the transfer of momentum between the vehicle and you. Once the acceleration has stopped the energy transfer is still taking place while you are in physical contact but is much less than during the acceleration phase.

Breaking this physical contact with the moving vehicle does not stop the transfer of momentum but the transfer is much less because now only the air (being much less dense than the seat) inside the vehicle is transferring the energy and the principal force acting on your body is now gravity. Momentum is now transferred to a downward direction and slowing down your forward momentum at approximately 32 feet per second per second.
Miles.