The Metra trains run with 90psi brake pipe. Two shoes on each wheel. Each shoe only 1/4 inch from the wheel when released. Locomotives run with 70psi, one shoe per wheel (granted the cylinder is larger, as well as the brake shoe). Shoes about 1" from wheel when released.
In my previous post, I mentioned that a LONG train can stop in about 1/4 mile. The short trains cannot. Reason: the braking effort on the coaches is far greater than on the locomotive.
I am unsure how much the alleged “proportional” braking effort is due to concerns about coupler strain (not too much stress with a train of only 800 tons). And I do not believe the buff forces of a passenger train in maximum braking negative-G to be sufficient to make derailment a concern, either.
And if you have ever rode on a suburban train with a less-than-enthusiastic engineer at the controls, you will discover how much slack there is on a suburban train, as the unbalanced braking effort becomes apparent by the locomotive running into and away from the coaches during braking.
futuremodal,
if I understand your idea correctly, the reason your idea might not work is the rigging would have to be lower that the top of rail in order to funtion.
Magnetic track braking definately doesn’t do that. It’s either on (dropped) or off (raised for transit.) The point was that no matter how long the train, or how strong the manget, or how many cars had it, one locomotive and two cars would probably be able to easily overcome any braking power provided by the magnetic brakes if every pair was applied at full pressure, locomotive, cars and all. They just don’t provide enough friction to effectively slow down a large (relative to a trolley or LRV or self-propelled car) train.
Magnetic braking will not generate enough stopping power at full capacity at any time on any train at any usefull speed, and doesn’t really work well on LRV’s as an emergency brake above 10mph or so.
They don’t add enough to help in an emergency (especially if the train is moving at speed-often 40 or 50 mph), and not on heavy trains, even just a loco and a few cars. Their uses are very specified, for holding LRV’s on a hill (not stopping the car-keeping it stopped), and occasionally for slowing down light trnasit trains-dmu’s and such, that don’t weight that much, and only in emegencys I bet, or for stopping where the wheels are slipping.
ON another note, how can METRA lcomotives run 20psi lower than th
Zardos I think your confusing brakepipe with brake cylinder.
straight air passenger equipment in USA is run at 110 lbs brakepipe, freight is run at or about 90 lbs brakepipe.
You forget about wet rails and other impediments, leaves, etc. to normal wheel braking. Modern light rail cars have magnetic track brakes to add braking power in emergency, not to replace air brakes. And modern light rail cars use conventional parking brakes, not magnetic track brakes as parking brakes, In many cases, such as the diesel River New Jersey Transit light rail line, the light rail cars share tracks with conventional freight trains. (Time-of-day separation)
The reason for the reduced pressure on the locomotive is due to it’s weight: too much braking effort on the locomotive would cause unwanted slack action in the train.
It is a trade-off between comfort for the passengers (less braking effort) and safety (more effort).
Ah, that makes sense. The locomotive needs to stop slower to keep from running the slack in or out (depending on weather its pushing or pulling.) That would be one uncomfortable ride, especially with the legnth of some METRA trains and those heavy double deck coaches.
Do Metra suburban gallery cars have tightlock couplers? I know the Highliner MU’s do, since all modern mu’s have tightlocks or Tomlinsons or Sharfenburgs to keep the electrical contacts in good shape, but what about the push-pulls? Modern mu’s handle electrical contacts via the couplers without separate cables. I forget how METRA does it on the push-pulls and would appreciate this bit of education. Obviously, adding additional emergency braking power will be of more advantage with less slack action and with tightlocks. Again, by no means would the track brakes in any way replace current airbrake operation, just give the added power where available to reduce stopping distance in emergency conditions only.
The Metra car do have the tightlocks. However, the older coaches (the non-stainless-steel) have developed some freeplay in the draft gear over the years, so they have a bit more slack. I never ran the new equipment; I would hope they fit a little tighter.
The electric power for the coache’s heat & lights are supplied via special 3-prong 440v cables; these are in addition to the 27-point jumpers between each coach.