A method and mechanism for initiating an emergency stop for an unattended railcar is disclosed. The method may include using a trip arm placed alongside the railway tracks at a designated stop point that may contact a portable trip-cock lever arm that extends out beyond the perimeter of the railcar if the railcar reaches the stop point as it moves along the track. The trip-cock lever arm may be attached to a valve that is connected to the pneumatic brake system of the unattended railcar. As the trip-cock lever arm rotates, the valve may open to release the air pressure in the pneumatic brake system causing the brakes to engage the wheels causing the railcar to stop.