. Railroad structures and estimates . rotection ofmain tracks where a siding, which may be used for standingcars, comes off the main track or any other track leading thereto,having a gradient of per cent or over toward the main line,so located that there is danger of a runaway car getting eitherdirectly or through an intervening siding to a main track. The type used is generally that having an operating standand target of its own, but in special cases where deemed ad-visable, the type having a target stand only and interlockedwith the switch is used, l, Derails should be located so that de
. Railroad structures and estimates . rotection ofmain tracks where a siding, which may be used for standingcars, comes off the main track or any other track leading thereto,having a gradient of per cent or over toward the main line,so located that there is danger of a runaway car getting eitherdirectly or through an intervening siding to a main track. The type used is generally that having an operating standand target of its own, but in special cases where deemed ad-visable, the type having a target stand only and interlockedwith the switch is used, l, Derails should be located so that derailed cars shall not foulthe protected track, and the distance of the derail from theclearance point should be carefullj considered with referenceto the probable distance a car would run after being derailed. Retaining or deflecting guard rails are used in special caseswhere deemed advisable. The terms Right and Left hand derail mean a deraildeflecting to the right or left in the direction which a derailedcar would move. (Fig. -73.). Left Hand Derail Fig. 73. The following is an illustration of the method of determiningthe speed of a runaway car at the derail. A car is standing on a siding 450 ft. from the derail. The fall of the track to the derail is Between thesepoints there is 2° 00 curve 200 ft. long. Rolling friction equals ft. per 100 ft. of travel,, or in 450 ft. it is X ft. Curve resistance equals ft. per 100 ft. oftravel per degree of curve, or in 200 ft. of 2°00curve it is 2 X 2 X ft. Total resistance expressed in feet of fall ft. The effective fall is - ft. Jl IMPACT OF CARS. 231 Let V = the speed of the car and h = the effective fall, thenthe general formula is r- = h -^ this case r- = ^ = 100,V = 10 miles per hour, the speed of the car at the derail. The proximity of other tracks, structures, embankments andcurvature of the track must also be considered. Formula for impact of cars
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