When do you use two locomotives in the front of the train and when one in the front and one in the back?

Question

I'm interested in cargo trains

Answer 1

The general procedure for me with NS is we are limited to the amount of powered axles (HP) we can have pulling on a train (headend) but that is generally 3 big 6 axle motors. Coming off the mountains with a coal train we are given two motors, which for the most part is all we need to get it to the next destination. When the trains tonnage is too great for the two motors, we stop and pick up a "pusher" (term used on the railroad) naturally he hooks on to the rear for an extra 8000 horsepower :) (he uses two motors where we are. If the coal train is under around 16,000 Tons, two motors will usually pull the few mile grade in this discussion, we also have other ways to tell such as if we are doing at least 33mph past a certain landmark, usually the train will pull the grade.  But there are lots of factors such as age of the motors, weather, engineer etc. that will affect making it up the hill.

Answer 2

Another factor these guys overlooked is sometimes the decision to put the helper on the rear of the train is for the ease of uncoupling it. Ordinarily, the helper is removed at a specific spot where it's no longer required. Less time is wasted by simply uncoupling at the rear and allowing the train to proceed.

Answer 3

when you are going up a steep hills

Answer 4

generally trains put the power on the head end....in mountian areas depending on the length of the train and the tonnage an extra engine in the middle or tail end to do some pushing is sometimes used , if you see an engine on the tail end it could be deadhead...getting a ride to be used at another station

Answer 5

practice around here for helpers is when they have to go upgrade with more than 8000 tons on these coal trains is 2 sd-70's on the front and 2 in the rear to get out of these mountain areas. csx in virginia and kentucky and norfolk southern here in tenn. both use pushers until they get on the less than 1% grades. we sit on our front porch and watch them all the time.

Answer 6

A loco is placed on the rear, or cut in mid-train, weather it be a manned helper or a DUP, when the force being exerted on the drawbar, due to the pulling power of the locos exceeds (Or gets dangerously close to) the drawbar limit. There are many factors which affect the force exerted on the drawbar. Tractive Effort, grades, train weight, loco power output (HP), curve resistance, etc..etc.

Answer 7

There is only so much tonnage that a coupler can handle before it, or the draw bar it fits into, literally gets ripped in two.  This amount of force increases when in grade territory as gravity adds to the force.

So, an engine is placed either in the train or at the rear of the train to lessen the forces on the couplers that are closer to the head end road engine.  These are called 'helpers'.

Though rare these days, it was common practice to sometimes use two helpers.  One placed in the train, called the 'swing' helper, and another behind the train, as the 'rear' helper.  Sometimes, trailing tonnage is not the problem when climbing a grade, but there is additional need for more horsepower.  In these instances, the helper will be added to the road engine, 'on the point'.  These days, the locomotives are MUed (Multiple Unit) controlled from the engine on the point.  But, when helpers are added that are not connected 'in multiple' but ran by a helper crew, this is called 'double heading', where the brake pipe is the only connection between the two power consists.

The helpers in or behind the train can be either manned or remotely controlled by the engineer on the road engine.  When used unmanned, these are referred to as DPU (Distributed Power Units) operation.

The DPUs are not used solely in grade territory though.  Often times heavy unit trains consisting of all coal hoppers or grain hoppers utilize the extra power even in flat or undulating territory, again to increase the amount of tonnage that can be handled.

Answer 8

it depends on how much weight is on the train versus the incline of the rails.

Answer 9

As Hoghead as stated, "helper" locomotives are employed when grades are so stiff (i.e., meaning a steep hill) that the lead locomotives need assistance from the rear (which today is common practice on long coal drags).  While usually only one or two helpers are needed today with diesels so powerful and able to achieve very high tractive effort it used to be common to also see mid-train helpers (which are just locomotives added to the middle of the train to give more help).

Answer 10

In a nutshell, there is only so much weight you can pull from one location, increased stress on the rails and couplers are the main reason.

So, after a certain point, the railroads have to decide whether to split the train in two or run extra power in the rear, either with an extra crew or more likely, with remote controlled locomotives.

There are computer generated models the RR's can use to determine when this is necessary, taking into account grade, curves, and total tonnage.

It varies from district to district.

Answer 11

I don't think it matters.  They both are propelling the train whether they are pushing or pulling.  The train goes by my house (within 50 feet) and I always see them together at the front for freight trains.  Maybe when the figure out that the train is too heavy for one, they add another engine at the back for convenience.

The Amtrak goes north frontward and the engine is at the back going south.  I guess there's no place to turn it around.