Positive-Train-Control

In a little less than five years, American railroads are to institute Positive-Train-Control (PTC), where off-locomotive computers override human input.
If a train exceeds its track-authority, a distant off-locomotive computer overrides the train-crew’s actions, activates the train-brakes, and brings the train to a stop.
Previously train-control was done by humans. Elaborate systems were in place to keep trains from crashing into each other.
But pile-ups occurred, occasionally with the volatile freight often carried by trains, dangerous chemicals and flammables.
Trains crash into each other causing massive fiery explosions, and/or release of toxic gases over a wide living-area, e.g. chlorine.
Sometimes such accidents were the result of human foul-ups allowing a train to exceed its track-authority.
Other times a train may just derail, or encounter a broken rail.
Two factors are at work that may not be apparent to a public used to highway transit.
—1) Trains share the same pathway, the track.
They can’t just steer around a threat to avoid it.
A second train following a first train has to be kept separate. They’re both on the same track.
If the first train stopped, the following train has to also stop. If not, it will dutifully follow the track right into the rear of the lead train.
—2) Trains can’t stop very well.
Slam the brakes of a highway vehicle into emergency, the wheels stop rotating, and the momentum of the vehicle overcomes the tires’ contact with the pavement.
The vehicle breaks into a lurid skid, which may continue on the pavement, or may go off into the boonies.
Whatever; the vehicle eventually stops, often in less than 100 yards.
Do that with a train, throw the train-brakes into emergency, stop the wheels from rotating, and the train may skid more than mile before it stops.
The contact-patch of steel wheel on steel railhead is tiny, compared to a tire on pavement.
Which is why trains can move so much more. There’s little rolling-resistance, which makes slowing difficult.
This has to be factored into train separation.
A following train has to be far enough behind to stop safely if its leader stops.
It used to be humans did this.
But humans make mistakes, with possible dreadful consequences.
So now humans are taken out of the picture, train-control by distant computers instead of human train-dispatchers — and engine men.
The locomotives are in constant radio-contact with far-away computers that can override human input.
Nice idea, but anyone familiar with computers knows they can hang.
If I am correct, I think Washington’s (DC) Metro service had Positive-Train-Control, yet it let a speeding Metro commuter-train plow into the rear of a stopped train.
With tragic results, including fatalities.
People immediately jumped on the train-engineer, but she’d been led into a trap.
She threw her train into emergency, but it just slid into the stopped train.
The accident also killed her.
Positive-Train-Control made the mistake; it switched her train over to the occupied track.
Physics were at play: -A) trains share the same track, and -B) it’s hard to stop a train.
There wasn’t much the train-operator could do.
I’ve heard it myself on my rail-scanner.
“Where we goin’? I see we’re being crossed over to Track One.”
This wasn’t the way it was driving bus.
You were dodging threats, but you could.
And if you needed to, you could stop fairly quickly.
You weren’t looking at a mile-long skid.
Another problem with Positive-Train-Control is incompatible systems, the fact that one railroad’s PTC may be different than another railroad’s.
It’s Macintosh versus PC, and never the twain shall meet.
That negates railroads sharing locomotives, or another railroad having trackage-rights.
Both BNSF and Union Pacific share Union Pacific’s Tehachapi line (“tuh-HATCH-uh-pee”). BNSF has trackage-rights.
Suppose Union Pacific and BNSF have incompatible PTC systems; can BNSF continue to use the Tehachapi line?
Probably most trains on the Tehachapi line are BNSF.
Another fear among railroaders is Positive-Train-Control may burp and stop everything.
Rendering rail transit useless.
At which point humans take over to maintain fluidity.
Expect that to happen, and foul-ups like Washington’s Metro.
Anyone who’s used a computer knows how it can become discombobulated and just stop.
Positive-Train-Control. A nice idea that might do more damage than it’s worth.
I get the feeling it’s more for computer-engineers than railroading.

• RE: “Driving bus......” —For 16&1/2 years (1977-1993) I drove transit bus for Regional Transit Service (RTS) in Rochester, NY, a public employer, the transit-bus operator in Rochester and its environs. My stroke October 26, 1993 ended that.
• Apple “Macintosh” computer versus PC (personal-computer), usually Microsoft Windows. (This computer is a Macintosh — fear and loathing among my siblings, who are all PC users. [Macintosh is of-the-Devil.]) —Both computer platforms are constantly at war with each other.
• “BNSF” = Burlington Northern Santa Fe, a major western railroad, a merger of Burlington Northern Railroad and Santa Fe Railroad a few years ago.
• The line through Tehachapi Pass in California is originally Southern Pacific, but SP was acquired by Union Pacific.