1 MARCH 2000
Table 3-4. Curve Compensation for a 1 Percent Grade
Degree of Curve
5. LOCOMOTIVE TONNAGE RATING.
a. Definition. The maximum weight of train that a locomotive is capable of pulling over a route is known
as its tonnage rating. Tonnage ratings are affected by many factors, but locomotive tractive effort and
ruling gradient are among the most important.
b. Application of the Procedures. The procedures for estimating locomotive tractive effort and tonnage
ratings presented below are simplified versions intended for route design purposes. They are not
intended to be used for the actual make-up and dispatching of trains.
(1) Tonnage Requirements, Locomotive Assignments, and their Effect on Route Design.
(2) The route must be designed to allow trains of sufficient size to travel over the finished line.
Maximum train size is determined primarily from usable locomotive tractive effort and the gradients and
curvature along the line.
(3) Designers must verify tonnage requirements with the appropriate transportation officers, as well
as understand the general operating plan for routine traffic, training exercises, and mobilization.
(4) On military railroads where government owned and operated engines are used, these engines
might handle all routine traffic, but during training exercises or mobilization, a commercial engine may be
expected to handle over-the-road operations, while the installation's engine takes care of switching and
short moves. Another option, when installations have more than one engine, is to use two engines for
maximum tonnage trains when such single train movements are required. Thus, in addition to tonnage
requirements, plans for locomotive use must also be known.
c. Determining Locomotive Tractive Effort.
(1) Locomotive Capability. When tractive effort curves are available for the locomotives to be used
on the line, tonnage ratings should be based on these curves. Otherwise, tractive effort may be
sufficiently estimated with the expressions in table 3-5.