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Braking Speed Simulation Tests—On February 20 and 21, 1991, the Safety Board conducted 11 computer simulated braking tests on a train dynamics analyzer at Freight Master, Inc., in Fort Worth, Texas. The track profile of the accident area and the physical characteristics of Amtrak train 66 consist were programmed into the simulator.
Additional conditions for each test were determined from the Pulse event recorder data and the reported operating procedures of the train's locomotive crew. According to the locomotive engineer and the recovered event recorder data, the apprentice engineer began braking Amtrak train 66 at the west end of the Ruggles Street platform (about 4,950 feet before the POD). Event recorder data show a maximum recorded speed of 109 mph approaching Ruggles Street.
In the simulator tests, the Safety Board used information developed from the manufacturer's braking graphs,[1] the Pulse event recorder data, and the described braking method. These simulated braking tests show that moving at 109 mph, Amtrak train 66 would not have slowed to 59 mph (approximate turnover speed) in 4,950 feet using the power braking method, unless the brakes had been applied in emergency at the Ruggles Street station platform. In addition, the train would have required at least 4,950 feet to reduce speed to 32 mph in emergency braking with the locomotive brakes fully applied. The turnover speed would have been exceeded in any full service braking sequence from 109 mph that the locomotive crew could have used from Ruggles Street. According to the manufacturer's braking graphs, in full service braking at 109 mph, the stopping distance would have been 9,010 feet.
Amtrak's Postaccident Actions
During the Safety Board's on-scene accident investigation, Amtrak installed an advance warning sign for the 30-mph speed restriction that is in effect between MP 227 and MP 228.3. The sign was positioned near the Pickle Factory (MP 225.7) Amtrak has also installed advance warning signs for speed reduction at locations on the Northeast Corridor that have similar slowing conditions.
In addition, Amtrak reports that it has altered the circuitry of the wayside automatic block signal at MP 226.2 (Ruggles), approaching Back Bay station, to display an "approach medium" signal aspect, indicating that the train is to proceed to the next signal at medium track speed (not exceeding 30 mph.) If a locomotive engineer fails to initiate automatic airbrake application after passing this signal, the automatic speed control system will cause a brake application. Amtrak reports that it has altered the wayside automatic block signals at five other locations on the Northeast Corridor that have similar speed reduction conditions.
Amtrak has also established a postaccident event recorder procedure that requires the locomotive event recorder to remain sealed until the Safety Board or the FRA arrive on scene to witness the removal of tapes.
- ↑ Data developed by the car manufacturer, in conjunction with the airbrake designer, to determine deceleration rates and stopping distances for the car series involved in this accident.
