I just returned from a trip to NE Kansas. While there I made a train watching stop at Perry and had the fortune of speaking with a UP Lineman working on a Grade Crossing. As we talked a Coal Drag passed and I asked about how fast it was going. He said 30 to 35. He went on to say that the max speed for coal trains was 39 mph explaining that a loaded 100 car coal train moving at 50mph will require 2 1/2 miles to stop. That astonished me and after thinking about I began to wonder if that might not be excessive. A friend directed me to a web site dealing with stopping distance but I’m unable to make heads or tails of it. Can anyone provide some imput?
I’m not sure on which line the maximum speed would be 39. 49 is the maximum for an unsignalled line. UP allows its coal trains 50 m.p.h. on lines on which the freight train timetable speed is 50 or better.
This doesn’t address the issue of stopping distance, because others are more qualified than I to answer that question.
Look at it this way, a loaded coal train can weigh in excess of 15,000 tons. 15,000 tons moving at 50 MPH is alot of energy to arrest. So 2 1/2 miles is not out of line.
I don’t have the answer to the stopping distance, just another related question. If the loaded coal train has a DPU on the end, how much does that reduce the braking distance?
A full service application will stop a loaded coal train going 50mph on flat ground in about 1.5 miles; an emergency application will stop it in about half of that distance.
Factors affecting the stopping distance are: temperature, grade (uphill or downhill), dynamic brakes (or the lack thereof), ice/snow accumulated in brake rigging, and to a lesser extent the condition of the rail.
A coal train (or any unit train) can usually be put directly into emergency without much risk of derailment due to all the freight cars are of equal length and weight. A manifest train with mixed loads and empties distributed at random needs much more care on how quickly the brakes are applied. A poorly blocked train (empties in front / loads on the rear) require muck more delicate applications of brakes (either dynamic or air) due to the likelyhood of undesireable slack action.
A suburban train can stop (under ideal conditions) from 70mph in about 1/2 mile.
Full service, and emergency braking are bad ways to stop a train at speed. While it probably won’t put anything on the ground, it’s a great way to snap a knuckle or pull a drawhead. According by latest Train Handling manual, air brakes are not to be used over 10 MPH (I think) except in an emergency. Speed is to be regulated with throttle modulation, and dynamic braking.
DPUs may reduce the stopping distance, depending on the company’s operating practices. There are limits to the number of axles used for dynamic braking. Improperly used dynamics will tear a train apart in seconds.
I have often read about the incredible amount of time it takes to stop high-speed passenger trains in Europe. I know this sounds silly, but I have often wondered if such trains could use “air brakes” for increased stopping power in emergency situations.
I know I will be laughed off the forum for saying this, but a parachute or other types of emergency-applied wind resistant applications–such as are found on airplanes–would give an incredible amount of resistance for a train moving well over 140 mph. If every car had such an emergency “air brake” integrated into its roof and the rear car and had an emergency parachute, I would have to think that the combined wind resistance would be formidable. Also, with the relatively light weight of passenger trains, such wind resistance might make a noticeable difference.
I know I should post such things at night so I can claim I was drunk when I wrote them, but it is something that always crossed my mind. Let the mockery begin . . . .
Well…given the fact that a parachute might snag a pole or bridge and have some extra, unintended braking power, wouldn’t an anchor be about as useful? //searches for rolling eyes smiley//[:P]
Claiming inebriation is a safe statement if you were posting at 1:00 AM but I’ll still be polite since the only dumb question is the one that you don’t ask.
When SNCF set the speed record of 205 MPH in 1955 or so, I read that the windows on the trailing coaches had to be opened after the speed run in order to create wind resistance to help stop the train, so your mind is thinking reasonably. If you’re thinking of something along the lines of speed brakes on a modern fighter, the main problem that I can see is the clearance diagram. A lot of catenary could get pulled down when the speed brakes are deployed.
My take on it though is that even though passenger trains are “relatively” light, they are still very heavy. The parachute might work to some extent, but not to any appreciable effect. And then there is the issue of overhead wires and bridges, and who / how would the chute get repacked after use?
I have often tried to think of ways to stop faster.
Years ago some passenger trains in the US (at least on the CNW) had cast-iron brakeshoes. While these offered significantly greater braking effort on dry, clean rail, the shoes also caused the wheels to slide very easily on any rail that was not in the clean, dry condition. This sliding of wheels caused many flats spots on the equipment, which is why they were discontinued from use.
Another problem to overcome would be the amount of momentum that a quickly-stopping train would transfer to the rails and subsequently to the roadbed. Mudchicken would have much more info regarding this. But I would venture to say that enough force transfered to the rails could cause a sunkink-like deformation of the roadbed or rails.
I remember learning (but I do not remember where, so don’t quote me) that it takes about 20 miles to make a station stop with the TGV, and about 5 miles for an ‘emergency’ stop. These distances sound excessive, and I wonder if anyone has any info regarding this. The 5-mile ‘emergency’ I consider possible, but the 20-mile seems a bit long. [Remember, at 180mph, it is travelling 3 miles per minute, so I can easily imagine taking a minute of more to stop from that speed.]
Gabe: Perhaps what you are describing would be along the order of a train car that had some sort of braking flaps that extend out from the outter body of car to make a much bigger wind resistance target? Think of those ugly, dancing lizards that can puff up the ruffled skin around their necks to appear bigger to predators. To work, the car would have to be designed so that the profile is no bigger than the width and height of the train itself. You wouldn’t ever know when such a braking application would be needed, and you wouldn’t want to snag a bridge or plug a tunnel.
I do not think it would take a large protruding brake to create a lot of resistance at speeds over 100 mph. Cantenery is a good point to consider–and I was thinking of something similar that to the brakes used on fighter jets. However, even if the brake would only protrude three feet from the roof of a car–so as not to interfere with the cantenery–or one foot from the side of the car, two of such brakes on every passenger car in the train would create a lot of wind resistence.
The excellent example of merely opening windows creating significant resistance, buttresses the claim that actual air brakes would creak considerable resistence.
As for the parachute, the problem of it becoming an anchor is well founded. But, it doesn’t have to be a 40-foot shute. I think a five-foot shute would create a lot of resistance. If it is jetisoned from the top of the car, I don’t think there would be too much trouble.
Finally, this would not be for regular applications–just emergency braking–so repacking would not be a major issue.
gabe, Your ideas are not so hair brain. In fact we (this forum) had this discussion a year or so ago when I posted the same type of topic. I seem to remember one of the last responses to the thread was someone posting that there is a high speed train in Japan that uses air grabbers as part of its braking system. I seem to remember there was a web link posted as well. Anyone else remember this thread?
According to that, maximum emergency stopping distance from 300km/h (186mph) is 3500m (about 2 miles), and each passenger car axle is equiped with 4 brake discs - with wheel slide protection. Of course, normal service braking would use dynamic/regenerative braking as much as possible, and normal braking rates have to take account of passenger comfort too - you don’t want the coffee sliding off the table [:)]
Cast-iron brakeshoes acting directly on the wheel treads have historically been the standard form of train braking. For higher performance braking (faster/heavier trains) brakeshoes fitted with composition friction materials (similar to that used for automotive brakes) have replaced them, or disc brakes are fitted instead - sometimes with wheel-slide protection added to cut down on wheel flats.
Consider this, friends: A Boeing 777 lands at about 140. It has rubber on concrete tires (very very good traction), computer assisted brakes (they operate at absolutely maximum efficiency), big spoilers for drag on the wings, and some 60,000 pounds of reverse thrust. It also takes a bit over a mile to stop. Seems to me that trains, with none of those advantages, do pretty doggone well!
Cast iron shoes may be standard on your side of the puddle, but I have not seen them in general use here since the early 70’s. And the cast shoes were far better at stopping a train on clean dry rail than the composition shoes (I’m only comparing direct stopping distances, not the increased maintenance costs associated with the cast shoes).
Another problem with the CI shoes is what is called ‘build-up’. As the shoe heats from the friction, a small amount of the metal is melted, and some of that fuses to the wheel. Once begun, the process is self-sustaining because the small amount of the original build-up tends to collect even more build-up (due to its slightly elevated position on the wheel). Soon you have a wheel which feels an