Distributed traction for freight

[JamesT]

For passenger operations, the general direction has been towards distributed traction with motors under many if not all carriages in a train. This does have various advantages over concentrating all the application of power to just one locomotive.
But I wondered if anyone had ever tried it in the freight world?
I don't mean having multiple locomotives, but having wagons with driven wheels. You would presumably need hefty electrical connections between wagons and your locomotive would essentially be just a transformer or a generator on wheels.
Would this be worthwhile for some types of freight? Or have I just come up with a solution in search of a problem?

 

[hexagon789]

For passenger operations, the general direction has been towards distributed traction with motors under many if not all carriages in a train. This does have various advantages over concentrating all the application of power to just one locomotive.
But I wondered if anyone had ever tried it in the freight world?
I don't mean having multiple locomotives, but having wagons with driven wheels. You would presumably need hefty electrical connections between wagons and your locomotive would essentially be just a transformer or a generator on wheels.
Would this be worthwhile for some types of freight? Or have I just come up with a solution in search of a problem?

Freight multiple units have been proposed, effectively a passenger multiple unit but with container carrying rather than passenger accomodation.

 

[MarkyT]

For passenger operations, the general direction has been towards distributed traction with motors under many if not all carriages in a train. This does have various advantages over concentrating all the application of power to just one locomotive.

I'd take issue with that statement. While for high speed trains in the Far East and Germany that is true, the latest French bi-level TGVs are using separate power cars with trailers between, and a similar approach is being taken for Alstom's new HS units for Amtrak in the USA. Talgo's latest high speed offering also retains a power car and trailer configuration and even Stadler's range of main line EMUs tend to concentrate traction motors on a select small number of vehicles within a unit. One of the main reasons for this is floor height. It is difficult to achieve level boarding at the standard European 760mm platform height with large-wheeled powered axles and traction motors beneath, while unpowered bogies are much easier to accommodate. DB has ignored this trend on its latest ICE4s and settled for a couple of steps up from platform level at every door to a higher floor, while in the Far East high platforms are generally used which match the traditional floor height of fully distributed traction units.

 

[Dr Hoo]

It is always a good idea to start with the ‘problem’. Freight already runs up to 60 or 75mph where feasible. Particularly for intermodal wagons (which are probably the ones where faster operation might be most beneficial) the low deck and small wheels make it hard to fit motors.

 

[edwin_m]

It is always a good idea to start with the ‘problem’. Freight already runs up to 60 or 75mph where feasible. Particularly for intermodal wagons (which are probably the ones where faster operation might be most beneficial) the low deck and small wheels make it hard to fit motors.

Indeed. Freight multiple units for containers were tried in Germany and elsewhere about 20 years ago but according to Wikipedia none is now in revenue use although they survive as tunnel rescue and other engineering trains. The Windhoff multi-purpose vehicles used by Network Rail are closely based on this design, but putting the engine underneath the deck makes it too high to carry standard containers in the British loading gauge - the various modules used for leaf clearing, de-icing etc are built to smaller diamensions. They were actually used in one of several abortive trials of small-volume container transport options, but in that case a standard flat wagon was inserted between the two halves of the unit to carry the containers themselves.

 

[MarkyT]

One thing that has been a trend for a while in places where very long trains operate, such as the United States or Australia, is to continue using conventional locomotives, but place them in clusters along the length of the train using remote control techniques. Some of these trains are so long today that putting all the locos on the front would result in unacceptable coupling forces, and having remote brake valves distributed throughout the train makes retardation far more controllable too.

 

[Mag_seven]

If "The Post" can be regarded as "freight" then we have the Class 325!

 

[LOL The Irony]

If "The Post" can be regarded as "freight" then we have the Class 325!

I believe the title of this thread is "Distributed traction", not shoved into 1 "locomotive" (trailer moter)

 

[JamesT]

It is always a good idea to start with the ‘problem’. Freight already runs up to 60 or 75mph where feasible. Particularly for intermodal wagons (which are probably the ones where faster operation might be most beneficial) the low deck and small wheels make it hard to fit motors.

I wasn’t particularly thinking of faster top speeds for freight, but more the opportunities for acceleration and keeping the speed up.
Would a heavily laden freight going up Shap find it easier with more powered axles (more “grip” if you will), than a single locomotive trying to drag wagons?
Or a freight held in a loop, would distributed traction allow it to get up to speed faster and allow it to use smaller gaps between passenger trains and minimise delays?

 

[furnessvale]

I wasn’t particularly thinking of faster top speeds for freight, but more the opportunities for acceleration and keeping the speed up.
Would a heavily laden freight going up Shap find it easier with more powered axles (more “grip” if you will), than a single locomotive trying to drag wagons?
Or a freight held in a loop, would distributed traction allow it to get up to speed faster and allow it to use smaller gaps between passenger trains and minimise delays?

Both can be achieved by more horses and/or axles at the front, or if necessary distributed along the train, in a dedicated locomotive(s).

There is no money to be made having expensive traction packages sitting in sidings while the wagons are unloaded and reloaded. In the time that occurs, the locos have been attached to a ready loaded set of comparatively cheap wagons and are well on their way back.

 

[DerekC]

Both can be achieved by more horses and/or axles at the front, or if necessary distributed along the train, in a dedicated locomotive(s).

Whilst this is obviously true, it would need a lot of horses (MW) to get a heavy freight to perform as well as a modern passenger train.

There is no money to be made having expensive traction packages sitting in sidings while the wagons are unloaded and reloaded. In the time that occurs, the locos have been attached to a ready loaded set of comparatively cheap wagons and are well on their way back.

I think this hits the nail on the head.

A point not mentioned yet is that a good reason for using distributed under-floor power rather than locomotives for passenger trains is that you get more carrying capacity per unit length of train. This is a significant advantage when you are coping with high demand into a terminal with (more or less) fixed length platforms. Freight doesn't suffer from quite the same problem. Although loop and sometimes block section length can be an issue the locomotive is a relatively small part of the length of the train, so the advantage is much smaller and is vastly outweighed by the disadvantages as above.

 

[43096]

I wasn’t particularly thinking of faster top speeds for freight, but more the opportunities for acceleration and keeping the speed up.
Would a heavily laden freight going up Shap find it easier with more powered axles (more “grip” if you will), than a single locomotive trying to drag wagons?
Or a freight held in a loop, would distributed traction allow it to get up to speed faster and allow it to use smaller gaps between passenger trains and minimise delays?

So for, say, the Mendip aggregates operation, how would you get around the need for bottom discharge doors? Not much space under there, and you still need cabs at the front and rear. And if you do find room for engines under the wagons, how does that affect weight and top speed as a result. You are also going to need multiple wagons with engines per train. Once you get over around 5 or 6 engines (and associated items such as motors, cooler groups etc), the maintenance costs make using one single large engine (a locomotive) cheaper.