JaBear just posted a nice picture on the Diner string of a unit train of tankers just coming onto a bridge in the Sierras. There's a big, blue covered hopper inserted behind the locos as the idler. It made me wonder:
1) are idlers commonly empty or are they acting in a revenue capacity?
2) if in revenue service, wouldn't that necessitate special and relatively inefficient shunting (and associated cost) for a single load and therefore be generally avoided?
3) will pretty much anything do as long as the weight is sufficient?
4) if the former, do most yards have a dedicated spur/siding where they're routinely available?
5) if empties, and they're not of the home road, are they tracked in the accounting system the same way as other "pool" cars would be?
Curiosity strikes again. Thanks, folks.
John (of Attu)
"Buffer" cars (the proper term here) are not revenue loads. They are added in for regulatory requirements to separate hazmat from the locomotives by at least one non-hazmat car.
It can be any non-hazmat, cars, but railroads operate a specific pool of assigned cars for buffer service, often specifically stencilled for buffer service only. These buffer-service-only cars will often be loaded/ballasted with something like sand to give them some weight and not run empty.
BNSF for example has a decent collection of old retired Airslide hoppers in Buffer Car service.
That said in a pinch, any available empty car could service; I've even seen somewhere a TTX center-beam bulkhead flatcar being used as a buffer once.
Chris van der Heide
My Algoma Central Railway Modeling Blog
Expanding the use of idler cars a bit, they were frequently used in carfloat operations to keep the heavier locomotives on solid ground. This helped reduce the load on the short carfloat bridge which needed to rise and fall with water level. It also helped maintain balance when loading and pulling rolling stock from the float.
I use short flat cars for idlers on my layout.
It takes an iron man to play with a toy iron horse.
cv_acr"Buffer" cars (the proper term here) are not revenue loads. They are added in for regulatory requirements to separate hazmat from the locomotives by at least one non-hazmat car.
As Chris said the buffer cars are added when there is a hazmat train that would not normally have the required cars to cover the hazmat.
The rules (Federal and railroad) require a loaded tank car placarded flammable liquid to be the 6th car from the engine, train length permitting, but not less than the second if train length does not permit.
Translating that into English, a loaded hazmat tank needs to have five cars of cover, but if there aren't enough cars of cover in the train, there has to be at least one car of cover. Since a solid unit train of tank cars has no cover (train length does not permit cover) the railroad has to add cover.
The "buffer car" is usually a load for train handling purposes (having an empty car right behind the engines folled by 75-100 loads is a derailment risk).
Since these are generally unit trains, the all the cars go between the shipper and consignee and aren't switched inbetween, once the buffer is in the service, it just stays with the set and there is minimal additional switching.
Dave H. Painted side goes up. My website : wnbranch.com
My understanding was that the buffer cars in hazmat service, more specifically oil-train service in the Blast Zone years, were ballasted with sand.
Idler cars are for allowing an engine to 'reach' a car across a carfloat, or on light or poorly-maintained or excessively curving track that won't safely support the engine if it couples directly. They are, therefore, usually as 'unloaded' or light as possible.
Additionally idler cars were/are used in circumstances where a load on a car is too long for said car and needs to overhang. http://www.railgoat.railfan.net/photos/otherrail/np/np056056_ron_hawkins.jpg as an example. (Used that one myself for building a load for some Athearn drop end gondolas I lettered for the NP. Whole story to that one.) There are also times where one of the idler cars might also be carrying frieght as well as being an idler car. Don't have a handy picture of that.
Idlers are used wherever the load needs to be separated from an engine or other car due to weight or the length of the load.
For overhanging loads (longer than one car), the idler can be on one end, can be on both ends, can be in the middle or can be both in the middle and on one or both ends. As Frrykid mentioned the idler can be loaded with some some material associated with the main load (fittings, braces, accessories).
For heavy loads there will be enough idlers to separate the loads or engines to meet the bridge or track loading ratings. Dead engine moves of many engines (10-20+) sometimes require idlers between each engine. Heavy duty multiple axle flat or Schanbel cars may require idlers to separate loads or loads rom the engiens. Float docks or other trestlework might require idlers to keep the engines off the bridge or trestle work.