From my understanding, the brake system is still pneumatic but works differently. Instead of the brakes applying on the first car, then the second, then third, etc as the drop in air pressure works its way back, this system triggers all cars on the train at the same time, so the whole train starts braking at once. On a train a mile or so long, that’d make a big difference.
I can imagine the cost would be huge, as every single railcar in the country would have to be retro-fitted. Some of those are owned by the railroads, others by the customer and still others by 3rd party companies. Since cars aren’t generally railroad specific (they may carry a particular road’s logo and reporting marks, but will easily travel on other roads) it would take all the companies converting to make it work. Only way I see it happening is if the FRA someday decides to mandate it.
That’s still the way the subways work, and virtually all of the time the doors won’t close fully if there is any substantial obstruction, and when there is no indication that the doors are fully closed, the train will not start. However, the conductor may get a doors closed indication when there is something thin between the doors, like the back of somebody’s overcoat. Usually if you are in the subway car, you will be able to pull the end of your coat into the car if it gets closed in the closing door.
Even if the equipment is functioning properly (and there are sometimes mechanical failures), there could be a situation when somebody is outside the car and with his or her bag or pocketbook trapped inside. If the strap is around a limb of the person, he or she could be dragged down the platform as the train starts to move. This would be an appropriate time to pull the emergency brake valve. BlakeTyner, perhaps you are thinking of regenerative or dynamic braking, by which braking force is applied by switching the electric motors so they operate like generators, slowing the train (a similar system is used in hybrid cars). Because electrical braking cannot bring a train to a complete stop or freeze a stopped train in place, among other issues, I believe that all trains using electrical braking use pneumatic braking for slow-speed brake application and as a backup for the electrical braking. The new cars in the New York City Subway fleet use dynamic braking.
Urinting on someone on a moving train is just wrong. Whatever happened to common decency? You know, the good old days of trainin’…when one would wait for a full stop at a station before urinating on another passenger.
Dynamics are a different animal. In long-haul freight, they only apply to the locomotive(s) and not the cars. The use of dynamics has the effect of bunching the slack, which is sometimes the last thing you want to do. The NYC subway cars are all mini-locomotives; they each have traction motors. In a long freight, the only traction motors are the ones on the locomotives.
When I think of electrical braking, I’m thinking of a system whereby an electrical signal (rather than the slower-moving drop in pneumatic pressure through the brake pipe) triggers the application of brake shoes to wheels. There is something vaguely similar in common use today, whereby the engineer can set his brake valve to emergency (triggering emergency braking from the front) and also push a button on his End Of Train controller device, which sends a radio signal to the little flashing unit on the coupler of the last car. It dumps air from the end of the train, making an emergency application from the rear. The two applications would meet in the middle, cutting in half the time it takes for the brake shoes to apply on the entire train.
If all the cars in the train were retrofitted with an electrical device, the brake application (not just in emergency) would be instant throughout the train. The brake shoes on the first car, the 100th car, and the last car would exert force on the wheels at the same time. With the way the system works now, the first car applies, then the second, then the third, then the fourth, etc. In some cases the last car will have absolutely no braking force a full minute after the engineer moves his valve.
The model I’m thinking of was featured in a Discovery Channel program (“Super Trains” maybe?) that came out about 4 or 5 years ago.
Since the OP has been answered and we have some railroaders in the room, I hope a hijack won’t be too offensive.
How does weather affect the operation of a train? Around here, we are having unusually cold and icy weather conditions. Highway bridges are sanded, schools are often closed, and officials are advising people to stay home. The trains, however, seem to be running as usual. Does ice on the rails not bother the train? Is there weather in which a train cannot operate safely?
All of the discussion of airbrakes on freight and Amtrak trains, plus dynamic/regenerative is true. However, the OP related to transit equipment, which can be a totally different animal. Depending on the equipment ordered, the brakes can range from the same airbrakes, to totally electrically operated disc brakes, and several levels of hybridization in between.
The DC Metro uses a system that is a combination of regenerative and electrically controlled pneumatic braking, FWIW.
BTW, the electrically operated airbrakes are being tested on several captive unit trains working the Powder River coal fields. They systems are designed to work the old fashioned way in the absense of power and control signals, but will be useless until enough rolling stock is in place to operate as intended. That makes for a self-fulfilling prophecy of failure; why pay for it and put it on if it won’t be used for 5 years?
VBob, 40 years the foamer
VunderBob, good point. I had my mind set on non-transit transportation. You’re absolutely correct, and brought up some things I haven’t heard.
Drum God, there are some weather conditions where trains can’t run. The primary one is flooding/standing water. If the water is high enough to make contact with the traction motors on the locomotives (located on the wheelsets) then it’s absolutely forbidden to take the train into it. Shorting out the traction motors is a Very Bad Thing ™.
Ice and snow isn’t usually a problem. There are a bunch of ways to remove snow from the track (winged pushers, rotary snow plows, etc.) but if it’s not a huge drift, the plow on the locomotive is usually enough. I don’t know that I’ve ever seen rails ice over (granted, I’m in the southern US) but for rainy or icy conditions, the locomotive carries its own supply of sand. Hoses stretch to just in front of the wheels, and the engineer controls when he wants it applied to the rail.
Switch points can get frozen, so they’re either heated or unfrozen with blow torches and such. In yards where cold weather is a problem, they’d generally be heated.
If the power gets knocked out, it can lead to the railroad slowing down or stopping, depending on the backup resources. I’ve never seen it happen personally, as outages are usually fairly brief and the battery system keeps the signals lit and the radio repeaters functioning.
The worst meltdown I’ve ever seen had nothing to do with weather, and everything to do with poor management decisions in the wake of the Union Pacific/Southern Pacific merger back in '97. Trains were stopped where they were, fully loaded, and sat for days and weeks. Congestion in and out of yards (especially in Houston) was terrible…it was not a good time to be a railroader for UP or a railfan.
Drum God, weather can affect trains in multiple ways:
Extreme Cold
As mentioned above, it can cause switches to freeze in position. It can also cause rails to break (though this isn’t too common).
Extreme Heat
Rails expand and can buckle. Overhead electrical catenary can expand and sag, fouling the pantographs on electric trains. Modern track-laying and overhead wiring techniques are gradually overcoming these problems. Rail can be laid onto heavy concrete sleepers (ties) rather than wooden ones. Then it can be clamped onto the sleepers with clips rather than the old fashioned dogspikes. These clips can exert a pressure of two tons, and whereas in the old days the rail would pop the dogspikes like they were nothing, and move the wooden sleepers as it expanded, these days the rail is held so securely it simply can’t expand. It’s a brute force solution. Still plenty of non-upgraded track around though. Rail can also be heated before it is laid and clipped into place - usually heated to the temperature of a warm to hot day, so when a real heatwave comes, it doesn’t need to expand as much.
Flood, snow
Steam locomotives could power through water up to the footplate. Modern diesel-electrics and electrics can’t handle more than a couple of inches above the rail because there are all sorts of electrical goodies in the bogies (trucks). Water and snow can interfere with the rail circuits for signalling, resulting in phantom trains occupying sections and causing real trains to be held up at red signals.
Rain
Just like cars, trains often have to slow down a little in the wet. You’ve got steel on steel to start with - add water and things get slippery. A train driver can lose his job if he “SPADs” (Signal Passed At Danger), so they tend to slow down.
Here’s one out of left field that most people don’t realise. On a largely above-ground commuter system like Sydney’s, passengers tend to string out along the length of the platform waiting for their train. But on a wet day, they huddle under the roof of the station building in the middle, and they also wait until the train has stopped and opened its doors before even approaching it. This might only mean the train has a “dwell time” at that station of ten seconds longer than normal, but on a route with thirty stations, you’re arriving downtown five minutes late. Then the train behind is held up at the signals and has the compounding effect of its own passengers taking longer to board, and after a few hours of the morning commuter rush, you’ve got massive delays to the system.