22 HIGHWAY CONSTRUCTION 



It is a common practice to run a mountain survey up hill, but 

 this should be avoided. Whenever an acute-angled zigzag is met 

 with on a mountain road near the summit, the inference to be drawn 

 is that the line being carried up hill on reaching the summit was 

 too low and the zigzag was necessary to reach the desired pass. The 

 only remedy in such a case is by a resurvey beginning at the summit 

 and running down hill. This method requires a reversal of that 

 usually adopted. The grade line is first staked out and its horizontal 

 location surveyed afterwards. The most appropriate instrument for 

 this work is a transit with a vertical circle on which the telescope may 

 be set to the angle of the maximum grade. 



Loss of Height. Loss of height is to be carefully avoided in a 

 mountain road. By loss of height is meant an intermediate rise in a 

 descending grade. If a descending grade is interrupted by the intro- 

 duction of an unnecessary ascent, the length of the road will be in- 

 creased over that due to the continuous grade by the length of the 

 portion of the road intervening between the summit of the rise and 

 the point in the road on a'level with that rise a length which is double 

 that due on the gradient to the height of the rise. For example, 

 if a road descending a mountain rises at some intermediate point to 

 cross over a ridge or spur, and the height ascended amounts to 110 

 feet before the descent is continued, such a road would be just one 

 mile longer than if the descent had been uninterrupted; for 110 feet 

 is the rise due to a half-mile length at 1 : 24. 



Water on Mountain Roads. Water is needed by the work- 

 men and during the construction of the road ; it is also very necessary 

 for the traffic, especially during hot weather; and if the road exceeds 

 5 miles in length, provision should be made to have it either close 

 to or within easy reach of the road. With a little ingenuity the 

 water from springs above the road, if such exist, can be led down to 

 drinking fountains for men, and to troughs for animals. 



In a tropical country it would be a matter for serious consider- 

 ation if the best line for a mountain road 10 miles in length or up- 

 wards, but without water, should not be abandoned in favor of a 

 worse line with a water supply available. 



Halting Places. On long lines of mountain roads halting 

 places should be provided at frequent intervals. 



