RAILROAD CURVES 157 



sin 60 26' 17* 



sin 71 25' 29" cos 39 57' 

 The two values of $ a are 60 17' 15" and 119 42' 45" 

 (=180 -60 17' 15"). As the observations were made in 

 the afternoon, the obtuse angle should be used. This gives 

 a = 2 X 119 42' 45" = 239 25' 30". The mean of the four hori- 

 zontal readings is 101 12' 8". Subtracting this from the 

 azimuth of the sun, the azimuth of the reference mark is 

 found to be 239 25' 30"- 101 12' 8"= 138 13' 22". 



RAILROAD CURVES 



CIRCULAR CURVES 



DEFINITIONS 



The line of a railroad consists of a series of straight lines 

 connected by curves. Each two adjacent lines are united by a 

 curve having the radius best adapted to the conditions of the 

 surface. The straight lines are called tangents, because they 

 are tangent to the curves that unite them. 



Railroad curves are usually circular and are divided into 

 three general classes, namely, simple, compound, and reverse 

 curves. 



A simple curve is a curve having but one radius, as the curve 

 AB, Fig. 1, whose radius is AC. 



A compound curve is a continuous curve composed of two or 

 more arcs of different radii, as the curve CDEF, Fig. 2, which 



FIG. 1 FIG. 2 FIG. 3 



is composed of the arcs CD, DE, and EF, whose respective 

 radii are GC, HD, and KE. In the general class of compound 



