. A manual of the principles and practice of road-making: comprising the location, consruction, and improvement of roads (common, macadam, paved, plank, etc.) and rail-roads . 106 THE LOCATION OF ROADS. Let A and B be the given points, and let the top and bottomlines of the slope to be ascended be considered parallel. Let71111 represent the length which the road up the hill must haveto ascend with the proper grade. Join the given points by astraight line, and between the points C and D, at which thisline meets the top and bottom line, establish a zigzag, of asufficient number of turns to make
. A manual of the principles and practice of road-making: comprising the location, consruction, and improvement of roads (common, macadam, paved, plank, etc.) and rail-roads . 106 THE LOCATION OF ROADS. Let A and B be the given points, and let the top and bottomlines of the slope to be ascended be considered parallel. Let71111 represent the length which the road up the hill must haveto ascend with the proper grade. Join the given points by astraight line, and between the points C and D, at which thisline meets the top and bottom line, establish a zigzag, of asufficient number of turns to make its entire length equal tomn, the development required ; which in the instance lastsupposed would be 3000 feet, the straight line CD being only1500. The road which ascends the Catskill mountain makes sevensuch zigzags or tacks. Their angles should be rounded off bycurves, as explained in a following article on Final these curves the width of the road should be increased, asdirected on page 46. Case 2. When the straight line meets the slope ohliquely,and the two given points are very distant from each other. Fig. Let A and B be the given points. Between the top andbottom lines of the slope draw a line mn at such a degree ofobliquity as will make its length equal to the development re-quired, which, in the instance supposed, is 3000 feet. Thestraight line AB would be too steep between C and E. There-fore from the point C draw a line CD, parallel and thereforeequal to mn. Join DB, and the line ACDB will be the onedesired. ESTABLISHING THE GRADES. 107 A zigzag between C and E would give a longer line; for,comparing the parts of the line thus obtained with those of theother, we find AC common to both; the zigzag CE equal toCD by construction ; and EB longer than DB, because fartherfrom the perpendicular. The construction above directed is merely approximatelytrue, becoming perfectly so only when the points A and B areinfinitely distant from each other. The strict co
Size: 2238px × 1116px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1850, booksubjectrailroa, bookyear1853
