<P> Manual hand brakes serve to keep a piece of rolling stock stationary after it has been spotted in a rail yard or at a customer for unloading or loading . They are also used to secure a parked train from inadvertent movement, especially while unmanned . </P> <P> Before the development of locomotive - actuated train braking systems in the late 19th century, designated railroad employees known as brakemen would move about the tops of cars, setting hand brakes in an effort to stop the train in a timely manner . This process was imprecise and extremely dangerous . Many brakemen lost life and limb as a result of falling from a moving train, icy and wet conditions often adding to the hazards involved in negotiating the top of a swaying boxcar . In the U.S., an 1893 federal law, the Railroad Safety Appliance Act, required automatic brakes on all railroads, effective in 1900 . </P>

When can the parking brake be used to stop the vehicle