LOCOMOTIVE OPERATOR WAS PUSHING EMPTY RAIL CARS ONTO A VACANT RAIL SPUR WHILE ANOTHER EE WAS SUPPOSED TO THROW A SWITCH. THE EE FORGOT TO THROW THE SWITCH CAUSING THE PUSHED RAIL CARS TO CORNE R AND COLLIDE WITH OTHER RAIL CARS. THIS CAUSED ABOUT 2500 WORTH OF DAMAGE TO THE RAIL CARS. THE LOCOMOTIVE OPERATOR EXPERIENCE MILD CERVIAL MUSCLE STRAIN.