One bulb from a set of lights that display track speed signals was missing from a Conrail locomotive after it collided with an Amtrak train, but the engineer said it was working before the crash, said William Bush, spokesman for the National Transportation Safety Board. The Conrail engineer, Richard L. Gates, said he saw an "approach limited" signal 1.7 miles from the accident site, which told him to slow to 40 m.p.h. But a tower operator 10 miles away said the first signal directed Gates to slow to 30 m.p.h. and be prepared to stop. A bulb was missing from a row of four signal lights inside the locomotive's cab. The Washington Post quoted an unidentified source as saying the missing bulb was the one that should have warned Gates a stop was imminent.