. Railroad construction, theory and practice; a text-book for the use of students in colleges and technical schools . cing the starting grade at stations. The resistanceto starting a train is augmented from two causes: (a) the trac-tive resistances are usually about 20 pounds per ton insteadof, say, 6 pounds, and (b) the inertia resistance must be inertia resistance of a freight train (see § 435) which isexpected to attain a velocity of 15 miles per hour in a distanceof 1000 feet is (see Eq. 140) 70 224p = ir_f^(152_o) = pounds per ton, which is the equiva-lent of a grad
. Railroad construction, theory and practice; a text-book for the use of students in colleges and technical schools . cing the starting grade at stations. The resistanceto starting a train is augmented from two causes: (a) the trac-tive resistances are usually about 20 pounds per ton insteadof, say, 6 pounds, and (b) the inertia resistance must be inertia resistance of a freight train (see § 435) which isexpected to attain a velocity of 15 miles per hour in a distanceof 1000 feet is (see Eq. 140) 70 224p = ir_f^(152_o) = pounds per ton, which is the equiva-lent of a grade. Adding this to a grade which nearly orquite equals the ruling grade, it virtually creates a new andhigher ruling grade. Of course that additional force can begreatly reduced at the expense of slower acceleration, but even §537, IMPROVEMENT OF OLD LINES, 595 this cannot be done indefinitely, and an acceleration to only15 miles per hour in 1000 feet is as slow as should be allowedfor. With perhaps 14 pounds per ton additional tractiveresistance, we have about 30 pounds per ton additional—equiva- S~*,il2>. Fig. 216. lent to a grade. Instances are known where it has provenwise to create a hump (in what was otherwise a uniform grade)at a station. The effect of this on high-speed passenger trainsmoving up the grade would be merely to reduce their speedvery slighth^ No harm is done to trains moving down thegrade. Freight trains moving up the grade and intending tostop at the station will merely have their velocity reduced asthey approach the station and will actually save part of thewear and tear otherwise resulting from applying brakes. Whenthe trains start they are assisted by the short down grade,just where they need assistance most. Even if the grade CDis still an up grade, the pull required at starting is less than thatrequired on the uniform grade by an amount equal to 20 timesthe difference of the grade in per cent. APPENDIX. THE ADJUSTMENTS OF INSTEUMENTS. The a
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