During my days as a carriage examiner I always found that pushing a barrow load of brake blocks was easier than pulling because, I think, the triangle of forces dictates that when pushing you are pushing into the ground and easily overcome friction and so roll along whereas in pulling there is quite an effort going into pulling the load up rather than along so wasting effort.
Has any research been done into whether this would apply to locomotives, as the coupler seems to be above the wheel centre and therefore pulling would appear to be less economical than pushing?
The dynamics of a rail locomotive (and of a train) are
very different to that of a flexible human body pushing a wheelbarrow, so you can't assume it also hold true for a locomotive.
The difference with a wheelbarrow is entirely down to the inefficiency of using your arms (connected to the body well above the centre of mass) to pull a load behind you. If a wheelbarrow is stuck, pulling backwards would actually be the best method as the last thing you would want is pushing it down to add more friction.
The reason pulling works with a locomotive is that it doesn't require the load to be help up like a wheelbarrow does, all the vertical work is done by the wheels on the 'other' vehicle holding it a fixed distance above the rails. And yes, while the coupler is usually above the height of the wheels that is nearly irrelevant thanks to the rigidity of a locomotive (relative to the human musculo-skeletal system at least) and the mass of all rail vehicles being high enough for the downward force due to gravity to easily cancel out any torque and have the couplers pulling horizontally - so long as the couplers are the same height above the rail at least.
Were you to try moving a vehicle supported at both ends (i.e. a car or a rail wagon) instead of a wheelbarrow, you would find that the ideal situation would be to push or pull in a horizontal direction as a rail coupling does. To push a heavier vehicle horizontally would mean lining up your arms with your centre of mass (i.e. getting the back horizontal) to allow your glutes and quads to do the hard work, while pulling would ideally be done using a torso harness instead of putting all the force through the shoulders and collarbone. Once you start getting really heavy stuff (e.g. the guys who pull buses or locomotives for show) you will see pulling is the preferred way.
Pushing is more powerful than pulling which is why bankers attatch to the rear and not the front
No, bankers attach to the rear for the sake of operational convenience.
It was at times normal for helpers to go on the front at certain mountain passes in the western USA before trains got long enough for distributed traction to become necessary for train handling purposes (i.e. preventing string-lining and run-ins). Helpers are not used as much these days, the operational inefficiency of the practice led to its demise in favour of giving the trains enough power for the whole journey.
If performance was really an issue they would put the extra loco on the front of the train for the whole trip to benefit from sharper performance away from stops and up other smaller hills, no freight trains in Britain being long enough for distributed traction to become necessary.
