Magnetic track brakes have been used on electric railways for over 70 years. The allegation that they tare up the track or damage it is false if they are applied in the usual manner, four track brakes to every two-trucked piece of rolling stock. They were standard on all PCC cars and all transit companies accepted the slight additional rail wear as a price for the greater safety and schedule speed the PCC cars and use of this brake provided.
Possibly the allegation results from trial use on a locomotive without any applied to the cars. Like airbrakes and unlike dynamic brakes, the braking must be distrubuted throughout the length of the train.
They are in use on the New Jerseuy Transit River Line, on the diesel electric railcars make in Switzerland by Stadler, a line that does have some street running in both Trenton and Camden.
Normal operation is for this type of brake to be used in emergency stops only. One exception was West Penn Railways and its subsidiaries. Much of the equipment consisted of fairly big and heavy center-door steel interurban cars without any air equipment, dating from before WWI. Regenereative braking was used, part of the energy used to heat in the winter, part returned to the overhead wire, and part fed directly to the magnetic track brakes. Final stop and parking was done by the conventional handbrake. Operation in traffic in large towns like Latrob, Greensburg, Conolsville, and Uniontown saw these big cars keeping up with traffic. In the country, cinder ballast from slag from mining was used, not rock ballast, but still the ride was smooth and tracks in good condition, even to the end of operations in the mid-50’s.
I don’t think magnetic track brakes are appropriate for loose-car freight trains, But for dedicated unit trains and suburban passenger trains, yes. For emergency use like on PCC cars.
But are only active during emergency braking, the cost of heaving brakes like that on freight cars or longer trains do not jhustefy the means as these brakes use high current low voltage and the cost of trainlining or providing per car would be to high.
Basicly a big flat brakeshoe with a set of coils mounted on it of about 3 feet long mounted on springs. It grabs/drags on railhead at high force when current is applied.
If you ever watch a PCCtrolley car you will see the bar between the wheels on the truck bouncing up and down whenever it moves. The spirngs are barely able to hold it up so that it can grip the rail when current is applied. I doubt they would be effective on train applications for two factors. One is weight and the other is the inordinate amount of power it would take to apply them assuming the engine could generate it. Plus every car would have to be shopped and wired and you would have two braking systems until all cars were converted which could be 20-30 years and a cost that would be outrageous. Once the thieves figured out there was copper for the taking half the cars would be stripped while the others were being grafttied. Not prctical and won’t happen in my opinion.
DK…Remember seeing these brakes on PCC cars after WWII in Johnstown, Pa…Not too far away from Latrobe and Greensburgh, Pa…Those same PCC cars also had {that still is impressive in my mind}, a type of wheel sets that mutted the noise produced of the streetcars…as compared to the loud clanging and whining noise produced by the previous older cars…
Most modern light rail cars have improved on the PCC resilient wheel and also have resilient wheels but with less maintenance, developed by Bochum in Germany and available from several manufacturers. And the construction of magnetic track brakes has also improved. Just check out the next modern light rail car you board, and look between the wheels. I agree completely it is not applicable to loose car freight railroading but very applicable to diesel push-pull commuter and even those Amtrak trains that use cabcars (some demotored FP-40’s), where the push-pull configuration and head-end power mean no additional cables between cars. It is all there already. All the equipment is also off-the-shelf. Modern multiple-unit cars already have electric control of braking, with the air-pipe pressure reduction just a back-up safety measure. In the case of Chicago, isn’t it a lot quicker and much less expensive and much less disruptive of neighborhoods than Chinese walls with underpasses at important streets? (Deep tunneling may be the long-term answer, but very expensive and requiring double-height tunnels to accomodate stack trains!)
I think I missed something here, but I presume the question had something to do with stopping trains or LRVs faster. Electric track brakes can do that, as the maximum retarding force is not related to the weight of the vehicle but to the strength of the magnets – put more current through the coils and you get more force holding the brake to the rail, hence you stop faster. They are a little tricky to modulate smoothly…
There are two significant considerations which I haven’t seen mentioned, however, with regard to train operation (less important with LRVs, but still significant). The most important is that they cannot be substituted for conventional air brakes. Why? Because they aren’t fail safe: if anything happens to the train (a break in two, for instance), conventional air brakes apply in emergency. If you are depending on electric track brakes, and you lose the electric power, you have no brakes – and a jolly ride for all concerned.
The second has to do with maximum stopping rate. Years ago the folks who designed the PCC car came up with a figure for maximum stopping ‘g’ forces. I forget what the number is right now, and it is in fact greater than you can achieve with air brakes – but not all that much greater. The improvement is worth it for LRVs, particularly those that operate on streets, do deal with the dimwits in cars, but might cause problems in regular trains with regard to passenger safety (you really don’t want folks falling down when you slam on the brakes, if you can help it).
…With all the conversation above re: electric magnetic brakes…I wonder if the older cars…such as units pre-WWII had them. I don’t remember seeing them…I can look in a book or so here to see but if they didn’t and people didn’t pay attention how they were driving {cars}, it’s a wonder we didn’t have more accidents between cars and street cars. I really don’t remember seeing any noticable accidents with street cars and cars back in that era…{In Johnstown}.
Okay, magnetic track brakes are basically large hunks of metal that are dropped down onto the rail head and electrified to magnetically try and stick them to the rail to stop a car. They are used primarily for emergency stopping.
I’ve run our Philidelphia all-electric PCC (#2709) (at the Seashore Trolley Museum) with only track brakes before. At main line speeds (30mph +) they don’t do all that much. This large mass (the track brake) dragging down the rail head will catch uneven rail joints, and anything that is not smooth on the top of the rail. (If used often enough, these will cause many more problems to the track then you would need to worry about with flat spots on the weels.) These brakes are mainly used to hold a car in place on a grade when transfering from brake to power (there is a delay, just as in a car.)
The difference between older and newer cars (pcc’s) is the brake system. Air-electric cars, with air brakes, have air brakes to stop the car. It is possible to apply power with the brakes partially on to keep the car from rolling. In an all-electric car, there is some delay between the dynamic brakes coming off and the power actually starting to turn the wheels, and this delay is enough to let the car roll backwards (downhill.) The track brake is dropped to stop this rolling. Track brakes are still used in Boston on modern Type 7 cars, for the very same reason.
All-electric cars were better because of how they stop the car. They don’t need a compressor, or any air piping, or even any brake shoes. All-electric cars actually work to stop the motors from turning instead of pressing shoes against the wheel treads. I think air-electric PCC’s still used brake shoes, which are a maintenance headake to keep balanced so that all apply and wear evenly.
]How would dynamic brakes hold a car on a hill? My understanding and experience with diesel locomotives is that the motors have to be moving for the dynamic to provide any retarding force.
It would look like if magnetic track brakes were to be used on freight trains in North America it would be on some kind of new concept unit train.
Some new European passenger sets have hydrolic brakes and have the same acuracy and smoothness of braking as an auto. Not as short a stopping distance but all air brake trains seem handle a little different. I heard this from talking to an train engineer from Denmark were they also use alot of GM deisels with the same air brakes as here.
Dynamic brakes don’t actually fully stop a car. They only work down to about 1mph. From there, the PCC uses a shaft brake to stop the driveshaft connected to the axles. (PCC’s don’t have “standard” drive with grears between the motor and axles. They use a driveshaft instead, but i’m not totally sure how this works.) With many other early trolleys with dynamic brakes, the final stop was often with a handbrake.
The largest problem with track brakes is that the rail is not designed to be a surface that takes wear. Track brakes drag along the top of the rail. Used enough, or on long trains (with a brake for each car) this would provide incredible wear on the rail. The rail doesn’t have steel wheels sliding on it all the time-they roll. Straight rail usually doesn’t get worn out very quickly. With standard brakes, the wear occurs between the wheel and the brake shoe, and it is very easy to change a brake shoe. Also, how would you power this track brake? Magnets need electricity (I"m still not sure track brakes are magnetic to pull them down), and this adds another system to add to each car, and it adds another need for power the locomotive needs to provide. Air brakes take power off the main locomotive’s engine shaft, and might add a little resitance to the engine, but not much. (You could try and use the current generated from dynamic braking to power the track brakes, but this gets overly complicated because dynamic power isn’t even current, and then all the locomotives and cars would need to be retrofit for this setup.)
I could see hydraulic brakes as an improvement, but desiging a system like that of air brakes would take a lot more work, and imagine how much hydraulic fluid an entire train would need-imagine if it ever leaked or spilled. Air is clean, and non-toxic.
Unit train or not, track brakes are a bad idea for long and heavy main-line trains. They aren’t effective enough, dropping large amounts of weight and dragging them down the rail is bad for the
My posting is to suggest that they be applied specifically to suburban railroad lines with multiple important grade crossings where grade seperation would be difficult and distructive to neighborhoods unless accomplished by very deep tunneling. They would be applied as they are on most modern light rail cars to be used in emergency situations only and not for service braking. They would not replace in any way the conventional airbrakes, which would be improved at the same time through electric control, with air-pressure reduction in the train airpipe kept as a backup, as on all current railroad diesel and electric mu cars (and on early streamliners). If they work out well in the suburban railroad application, then possibly they should be applied to push-pull and mu Amtrak intercitiy trains, where the car train-line circuits are also already in place (in place in all push-pull trains). If successful in avoiding accidents in this second application, then the next step might be unit trains withh dedicated consists, and then a fourth step might possibly be high-speed intermodel equipment . I do not see them ever being applied to typical freight cars for loose car freight railroading.
Another issue not mentioned regarding greatly increased braking force on passenger equipment is the effect large negative-G forces would have on the passengers.
Commuters do not stay in their seats until the train stops–they usually start getting up and go to their exit as soon as the train departs the previous station, so they can be first off at their stop. If you were to apply excessive braking force, you would knock down commuters like bowling pins, resulting in many injuries and many more lawsuits. Traincrews on passenger trains are always listening for the sound of the air dumping, because they know that means it is time to either sit down or grab something securly mounted.
The Metra coaches have two brakeshoes for each wheel (4 per axle). Combine that with a 90psi brake pipe and using the 2.5/1 ration of effective brake pressure (assuming a fully charged trainline), a direct-to-emergency application results in a 225psi application. And being as a long (5+ coaches) commuter train can actually stop RELATIVELY quickly already (about 1/4 mile from 70mph), much more braking effort is not really needed. And in addition, a greater braking effort via brake shoes would also cause the wheels to pick up during applications, especially in damp weather and/or when there are leaves, oil, or grease on the rails.
But if a system could be developed that would be used only in a true emergency (avoiding a collision or stopping short of a structural defect), then of course all the additional braking you could generate would be useful.
The CNW engineers that were the generation before me used to tell me of the days of the inter-city passenger trains, when the coaches were equipped with cast-iron brake shoes (instead of composition shoes used today). They claimed you could just about stand a train on it’s nose, the braking effort was so great. What also was great was the tendency for the wheels to pick up during hard or emergency applications, resulting in numerous
Regarding track brakes, what if the system was designed to contact the outer top of the rail rather than the portion involved in the rail-wheel point of contact? Then it would be less of a concern regarding wear on the rail, because wear on the outside of the rail will have no impact on the rail-wheel contact portion.
A. Relatively short passenger trains that need to stop really quickly (talking about three-four cars max i’d think)
B. Light rail trains that use them to hold the car on a hill (engange while the car is stopped only).
Track brakes are the last emergency stopping system (much like people joke to put your head between your knees and kiss you behind goodbye-not really doing anything, just hold on for the ride). They are really last, last ditch efforts for stopping. THeir primary use is to hold cars on a hill, they drop when the car stops (because dynamic brakes doesn’t do anything while stopped). Some trains use them for actual stopping power, but there are very small and short trains mostly like light rail, or some electric commuter service, not like locomotive-hauled trains today.
The weight of one locomotive would probably overwhelm the entire track-braking force of the entire train (even with two or three cars, with more cars (= more weight) the effect would be even less.) The faster a train goes when it applies the track brake, the less it’s goning to do. It would be like throwing an anchor on a chain out the back of you car going down a highway. It would take a while to stop, and on top of that, it would tear up the road.
Track brakes need all the surface they can get to try and stop a train. The rail is also profiled, and having a track brake hang down on the outer edge would wear away one side of the rail head, and it would then get thinner. This is even worse than having it make the top a little bit shorter. Track brakes also add weight to a train. They need room for the giant mass of iron/steel to be hung on a truck (one for each side), and they need another electrical system to make them work, and their effect is probably neglible for actual stopping power. That, and this is a lot of weight hanging from a truck. A PCC weight around 20 tons (figure one track brake per 15 tons for more modern 3-truck light ra
Of course the locomotives would be equipped with the magnetic track brakes as well. Modern commuter equipment carefully balances the aircyliner pressure on the locomotives with that on the cars to give braking effort proportional to weight of the particular vehicle to avoid undue strain on couplers and to keep the train on the track in an emergency. In some cases braking effort is even coordinated with overall weight meaning passenger loading, as measured by deflection of air springs! All this consideration would be applied to the emergency magnetic track brakes so the braking effort would be applied as evenly as possible, even though only in emergencies.