Few points are to be cnsidered here.it is not only the no of bogies that matters for loco allocation but also the no of stoppages.how far the stopages are.no of curves and so on.if 12827 was having few stops wap4 would hav sufficed but 12827 has many stops along with an aggresive tt.along with it it has to tackle the "s"crossing at most of the stns from mdn to adra in tge up line.that hampers its running.a wap4 accilaration is not enough for covering of time if it is running late .a wap7/wap5 would suffice the cause.as time will be saved controllers will be forced to run it on time.also a help that may come if all up line platforms are constructed at all stns from mdn to adra.that will cut down delay n speed up d train and also if in future adra grb double line comes up.but as...
more... of now wap7 is a need for hwh prr sf exp but it would never get it as loco is given by rnc which is why i keep saying rsa has destroyed hwh prr sf exp