In the location of new railways and the improvement of linesalready in operation, it is now well recognized that large economiescan be effected by the careful study of train resistance due to gradesand alignment, distributing this resistance so as to secure a minimumcost of operation with the means available for construction.
While engaged in such studies some years ago, the attention of thewriter was attracted by the fact that the usual method of calculatingthe traction of a locomotive—by assuming from 20 to 25% of theweight on the drivers—was subject to no small modification in practice.
In order to obtain a working basis, for use in relation to thisfeature, he undertook the collection of data from the practical operationof various roads. Subsequent engagements in an entirely differentdirection caused this to be laid aside until the present time. Theresults are given in Table 1, from which it will be seen that thepercentage of driver weight utilized in draft is a function of thelength as well as the rate of grade encountered in the practical operationof railways.
In this table, performance will be found expressed as the percentageof the weight on the drivers which is utilized in draft. Thisis calculated on a basis of 6 lb. per ton of train resistance, for dates[322]prior to 1880, this being the amount given by the late A. M. Wellington,M. Am. Soc. C.. E.,[A] and 4.7 lb. per ton for those of 1908-10, asobtained by A. C. Dennis, M. Am. Soc. C. E.,[B] assuming this differenceto represent the advance in practice from 1880 to the presenttime. Most of the data have been obtained from the "Catalogue ofthe Baldwin Locomotive Works" for 1881, to which have been addedsome later figures from "Record No. 65" of the same establishment,and also some obtained by the writer directly from the roads concerned.Being taken thus at random, the results may be accepted asfairly representative of American practice.
Attention should be directed to the fact that the performance ofthe 10-34 E, Consolidation locomotive on the Lehigh Valley Railroadin 1871 is practically equal to that of the latest Mallet compounds onthe Great Northern Railway. In other words, in the ratio betweenthe ability to produce steam and the weight on the drivers there hasbeen no change in the last forty years. This would indicate that thefigures are not likely to be changed much as long as steam-drivenlocomotives are in use. What will obtain with the introduction ofelectric traction is "another story."
These results have also been platted, and are presented in Fig. 1,with the lengths of grade as abscissas and the percentages of weightutilized as ordinates. The curve sketched to represent a generalaverage will show the conditions at a glance. The results may at firstsight seem irregular, but the agreement is really remarkable when thevariety of sources is considered; that in many cases the "reputed" rateof grade is doubtless given without actual measurement; that theresults also include momentum, the abili