24 HIGHWAY CONSTRUCTION 



Zigzags. The method of surmounting a height by a series of 

 zigzags or by a series of reaches with practicable curves at the turns, 

 is objectionable. 



(1) An acute-angled zigzag obliges the traffic to reverse its 

 direction without affording it convenient room for the purpose. The 

 consequence is that with slow traffic a single train of vehicles is 

 brought to a stand, while if two trains of vehicles travelling in opposite 

 directions meet at the zigzag a block ensues. 



(2) With zigzags little progress is made towards the ultimate 

 destination of the road ; height is surmounted, but horizontal distance 

 is increased for which there is no necessity or compensation. 



(3) Zigzags are dangerous. In case of a runaway down hill 

 the zigzag must prove fatal. 



(4) If the drainage cannot be carried clear of the road at the 

 end of each reach, it must be carried under the road in one reach only 

 to appear again at the next, when a second bridge, culvert, or drain 

 will be required, and so on at the other reaches. If the drainage can 

 be carried clear at the termination of each reach, the lengths between 

 the curves will be very short, entailing numerous zigzag curves, which 

 are expensive to construct and maintain. 



Final Location. The route being finally determined upon, it 

 requires to be located. This consists in tracing the line,, placing a 

 stake at every 100 feet on the straight portions and at every 50 or 

 25 feet on the curves. At the tangent point of curves, and at points 

 of compound and reverse curves, a larger and more permanent stake 

 should be placed. Lest those stakes should be disturbed in the 

 process of construction, their exact distance from several points 

 outside of the ground to be occupied by the road should be carefully 

 measured and recorded in the notebook, so that they may be replaced. 

 The stakes above referred to show the position of the center line of 

 the road, and form the base line from which all operations of con- 

 struction are carried on. Levels are taken at each stake, and cross 

 levels are taken at every change of longitudinal slope. 



Construction Profile. The construction or working profile 

 is made from the levels obtained on location. It should be drawn to a 

 horizontal scale of 400 feet to the inch and a vertical scale of 20 feet 

 to the inch. Fig. 7 represents a portion of such a profile. The 



