. Railroad construction, theory and practice; a text-book for the use of students in colleges and technical schools, and a hand-book for the use of engineers in field and office . cks up theriders and carries them back to the hump. The aggregatetime saved justifies the expenditure. The scale grade has beendesigned in each case so that each car will pass over the scalewith a maximum velocity of four miles per hour, which meansthat the car shall be entirely on the scale platform for a minimumtime of three seconds. Although the grade over the scales maybe as high as 1% for motion weighing, the we
. Railroad construction, theory and practice; a text-book for the use of students in colleges and technical schools, and a hand-book for the use of engineers in field and office . cks up theriders and carries them back to the hump. The aggregatetime saved justifies the expenditure. The scale grade has beendesigned in each case so that each car will pass over the scalewith a maximum velocity of four miles per hour, which meansthat the car shall be entirely on the scale platform for a minimumtime of three seconds. Although the grade over the scales maybe as high as 1% for motion weighing, the weighing mechanismmust be installed on a level plane and the weighing rails areblocked up to the desired grade. 408 RAILROAD CONSTRUCTION. §381. 381. Ladder tracks. Twenty-seven types of ladder tracksare shown in the 1917 Committee report to the A. R. E. A., butnearly one-half of the ladders reported in actual use belong totype a, Fig. 166a, and about one-half of the remainder belong totypes h and c. The other twenty-four types are chiefly expansionsand developments of the three types shown. Note that in typesa and c, the switches are, in each case, in a straight line along. Fig. 166a.—Types of Ladder Tracks. one of the tracks, which simpHfies the working of the switches,whether they are worked from a tower or on the ground by Track scales. Ihe standard design for a hump yard,§ 380, shows a track-scale grade, as an integral part of the design,located just beyond the hump. It has been found that it ispracticable to weigh cars with suflicient accuracy while the cai:sare in motion, provided the speed does not exceed 4 miles perhour, or 5;87 feet per second, and provided that the lergth ofthe scale is such that the car is entirely and alone on the scalefor a minimum of three seconds. This condition will be ful-filled when the scale is feet longer than the distance fromfront to rear axle of the car. Scales with lengths of 50, 56 and 60feet are considered standard. T
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