In steam days
Southern Pacific trains eastward across
Nevada and
Utah faced nothing steeper than 0.43% in the 531 miles from
Sparks to
Ogden—except for a few miles of 1.4% east of
Wells. Trains would leave Sparks with enough engine to manage the 0.43% grade (e.g. a
2-10-2 with a 5500-ton train) and would get
helper engines at Wells; the "ruling grade" from Sparks to Ogden could be considered 0.43%. But nowadays the railroad doesn't base helper engines at Wells so trains must leave Sparks with enough power to climb the 1.4%, making that the division's ruling grade. As such, the term can be ambiguous; and is even more ambiguous if the ruling grade is impacted by the effect of a momentum grade. Overland Route trains from
Sacramento, California to
Oakland face nothing steeper than 0.5% on Track 1, the traditional westward track, but nowadays they might need to approach the Benicia bridge on Track 2, which includes 0.7 miles at about 1.9% on otherwise near-level track. Using this as an example, several issues arise on defining "ruling grade". One issue is whether a running start should be assumed and, if yes, the speed to assume. Another issue is the train length to assume, given that certain lengths exceed the length of the hill in question. And if a running start at some arbitrary speed is assumed, the calculated "ruling grade" will be different for locomotives having different power-vs-speed characteristics. In the
United States, Congress set the Standard Grade for railroads eligible for subsidies and grants in the 1850s. They took as that standard the one adopted by the Cumberland – Wheeling Railway, that grade being or 2.2%. Later when charters were drawn up for the Canadian Pacific Railway in Canada and for the Union Pacific Railroad, the national governments imposed the Standard Ruling Grade on the two lines because each received federal assistance and regulation. (Vance, JE Jr.,1995) == Curve and Gradient Books ==