Many factors determine how long it takes to stop a train,
Load plays role in distance a braking freight would travel.
Trains stop in their own time.
Every freight train, every situation, every load is different. The distance it takes to halt a train in an emergency is based on multiple factors: its speed when the brakes are applied, the track’s incline, the number of cars hooked behind the locomotives and the loading of those cars, the “brake delay” inherent in the train’s hydraulic system, the friction-causing metallurgy of the wheels and tracks, the weather.
Even the engineer behind the controls can’t know on any given day how long it would take to stop the train.
“There is no specific rule of thumb on that,” said Greg Udolph, general manager of the Texas State Railroad, a freight and tourist line in East Texas running from Palestine to Rusk. “If the track is wet with dew, it changes. Everything that can affect it does. A train takes as long to stop as it takes to stop. Sometimes it can be a mile. Sometimes it’s less, sometime’s it’s more.”
So even when a conductor sees someone far down the track, the train may not be able to stop in time. Federal guidelines tell commercial drivers to immediately evacuate a vehicle that gets stuck on the tracks.
The public doesn’t yet know at what point the CSX Transportation train engineer perceived Tuesday afternoon that the bus stopped up ahead on the tracks in Biloxi, Miss., was not going to move, and decided to hit the emergency brake. The train was going 26 miles per hour when the engineer applied the brakes, investigators with the National Transportation Safety Board said Thursday at a Biloxi briefing. And the freight, running on a long straightaway through the coastal town, had slowed only to 19 mph when it hit the Echo Transportation tour bus high-centered on a hump-shaped crossing.
The train and crumpled bus came to a stop 203 feet down the track, officials said. Four Texas tourists died, and 35 others were hospitalized with injuries.
The train set was of medium size as freights go, with three locomotives and 52 cars. Information on the degree to which the cars were loaded has not been released. The stopping distance would vary widely, Udolph said, depending on that loading percentage.
Train brakes are activated by air pressure, he said. Each car in the line has a pipe running along its undercarriage, and those pipes are connected by hoses where the cars meet. Then, before the train departs, that pipe system is pressured to 90 psi, said Udolph, who was a train engineer earlier in his career.
When an engineer hits the brakes in a normal situation, some of that air bleeds into the attached brake cylinders, in turn pushing brake pads against the wheels throughout the train. The pipe pressure might drop only to 80 psi, for instance, he said.
“When you put a train into emergency, it drops that pressure from 90 psi to zero,” Udolph said. “Basically, it puts the brakes on as hard as you possibly can.”
Depending on the length of the train, there might be a few second delay between when the engineer hits the emergency brake and all cylinders throughout the train have been pressured up.
“Once you put on the emergency, you just hang on and wait for it to stop,” Udolph said. “You don’t know. Some engineers don’t have to do that their entire career.”
He never had to, never had that moment where human lives were at stake in front of his eyes.
“That is the longest couple of minutes in an engineer’s life,” he said. “I know a lot of engineers who have gone through it. It’s not an easy thing to come back from.”