> I'd like to assign motive power based upon tonnage of freight
trains.
Grades are a huge consideration --
Rules of thumb --
5 hp/ton on 0% grade (flat land)
25 hp/ton on 1% grade
45 hp/ton on 2% grade
65 hp/ton of 3% grade
Also remember it takes an equal amount of BRAKING POWER to hold back
a train on a downgrade. This is why dynamic brakes were rapidly
adopted
and why dieselization was so swift on steep mountain grades. A
diesel
powered train with dynamics can control the train speed with very
limited
use of train brakes.
You can make far more complicated calculations, of course. Steam
locos
reach peak HP at mid-range speeds (30-40 mph) while diesels can
maintain
constant HP. Normal DC traction motors couldn't handle slower speeds
than
10 mph for very long or they would overheat. Steam booster trucks
worked
only below 20 mph I think. Also, cold freight car bearings have
higher
resistance than warm bearings.
And don't get Mike started on Tractive Effort! :-)
