HIGHWAY CONSTRUCTION 17 



description of each bench mark should be recorded in the level book. 



Cross Levels. Wherever considered necessary levels at right 

 angle to the center line should be taken. These will be found useful 

 in showing what effect a deviation to the right or left of the surveyed 

 line would have. Cross levels should be taken at the intersection of 

 all roads and railroads to show to what extent, if any, these levels 

 will have to be altered to suit the levels of the proposed road. 



Profile. A profile is a longitudinal section of the route, made 

 from the levels. Its horizontal scale should be the same as that of 

 the map; the vertical scale should be such as will show with distinct- 

 ness the inequalities of the ground. 



Fig. 5 shows the manner in which a profile is drawn and the 

 nature of the information to be given upon it. 



Bridge Sites, The question of choosing the site of bridges is 

 an important one. If the selection is not restricted to a particular 

 point, the river should be examined for a considerable distance above 

 and below what would be the most convenient point for crossing; and 

 if a better site is found, the line of the road must be made subordinate 

 to it. If several practicable Crossings exist, they must be carefully 

 compared in order to select the one most advantageous. The follow- 

 ing are controlling conditions: (1) Good character of the river bed, 

 affording a firm foundation. If rock is present near the surface of 

 the river bed, the foundation will be easy of execution and stability 

 and economy will be insured. (2) Stability of river banks, thus 

 securing a permanent concentration of the waters in the same bed. 

 (3) The axis of the bridge should be at right angles to the direction 

 of the current. (4) Bends in rivers are not suitable localities and 

 should be avoided if possible. A straight reach above the bridge 

 should be secured if possible. 



Final Selection. In making the final selection the following, 

 principles should be observed as far as practicable. 



(a) To follow that route which affords the easiest grades. The 

 easiest grade for a given road will depend on the kind of covering 

 adopted for its surface. 



(b) To connect the places by the shortest and most direct route 

 commensurate with easy grades. 



(c) To avoid all unnecessary ascents and descents. When a 



