This example demonstrates that better Human Factors Engineering is needed. Why and how does an engineer lose track of the signals and ask, "What was that last signal?" Perhaps additional signals are needed instead of just 2. They are especially needed as a reminder after an event distracts the engineer. One such need is when a station is after the last yellow light. The engineer can be distracted by the station and forget. The NTSB stated this was a contributing cause in the 1996 Maryland crash; a crash similar to the Chatsworth crash.