Your train wouldn't have derailed if You applied the automatic brake the reason why Your train didn't slow down enough and derailed on that curve is because You applied the "independent brake" not the "automatic brake" when You applied the independent brake You cause the entire train to go into a buff event which didn't allow the train to slow down even further and caused the train to derail on the curve !!! remember that the automatic brake applies brakes on the entire train and the independent brake applies brakes on only the locomotive and it's tender