Trains have pneumatic brakes on every car that activates simultaneously since the late 1800s. More info at
http://en.wikipedia.org/wiki/Railway_air_brake
José
Well, close, but not entirely. Train brakes come on sequentially, from the front of the train to the rear. When the engineer reduces the pressure in the "train line", the air line that supplies air throughout the train, it sends a signal to each car to begin allowing air from reservoirs on each car to begin flowing into the actuator cylinder to apply mechanical force to the brake shoes/wheels. Because the pressure reduction starts at the front, it takes some time for the pressure reduction to reach the rear of the train and apply the brakes. Correspondingly it takes time for the brakes to release as well.
If a train goes into an emergency application "big holed"
and the train has a device on the rear car that reports train line pressure to the locomotive as well as receives commands, then big holing the train will also vent the train line from the rear. This applies the brakes from both ends at once. It not only speeds the process, but it also stretches the train, reduces the likelihood of a derailment due to the slack in the train "running in" suddenly. the term "big hole" comes from the fact that the venting of the air in the train line is not metered, but is "dumped" through a "big hole". As cold as it may seem, a train loaded with hazardous materials, like a few tank cars of methyl ethyl death, may not big hole the train in a futile attempt to keep from hitting a vehicle or trespasser on the tracks if the risk of a derailment is great, and the risk of greater loss of life exists.
I have been on 20,000 ton coal trains more than 8,000 feet long, running 50 mph when they went into emergency, and let me tell you it is scary slow to decelerate. Once big holed, it just keeps on going the same speed for what seems like forever before you see the slightest hint in deceleration. Add in a (slight) downgrade and it could take 2 miles to stop.
I take it that none of you live in an area full of trains and switch yards.
It doesn't take long to learn to really hate trains and the arrogant way that they are operated.
And, it doesn't take long to figure out that if you don't get across in front of the train, you could be in for a 30 - 60 minute wait. And, it's not unusual for a gate to be down all day with no trains around.
Even if it's just a single engine and no cars, you don't assume that there won't be a wait because there is a chance that the engine will stop in the in intersection to wait while someone does something somewhere else.
You get complacent.
Big surprise.
In
every state, the law states "motorists shall stop not closer than 15 feet from the near rail and not farther that 50 feet from the near rail and proceed when safe to do so".
Do you do this at every crossing? Didn't think so, but then neither do I, and I should know better. Like the guys that move near the airport and complain of the noise, your options are limited. Learn to be patient, or alter your driving patterns. Almost every city/town has ordinances that prohibit trains from blocking crossings of public through fares for more than a few minutes (5 or 15) because is can block emergency vehicles from responding to their duties. If you see a train stopped for a while longer than you think is legal, call the cops. They
will ticket the crew, usually the conductor, who does not operate the engine, but is administratively in charge of the train. A stationary train, like an airliner on the ground is not producing revenue.
Arrogance is not in the equation.
And yes, people are stupid around trains. As expert witnesses we have drawers and drawers of photos of dead men, women and children to prove that. It makes you physically sick to see the carnage caused by inattentiveness/cellphones, and just stupid bravado on the part of drivers and pedestrians alike, and don't get me started bout iPods and earphones and trains. Trains chop you up like a butcher gone mad. Many times the police report indicates that the responders were unable to locate all the pieces and returned in the daylight to complete the grisly job. The emotional effect on a train crew that just killed a family is something to behold as well. These guys carry that with them the rest of their lives.