20 HIGHWAY CONSTRUCTION 



inclination might be given to a road as an equivalent to a given de- 

 crease in its length ? To satisfy this question, the comparative force 

 required to draw different vehicles with given loads must be known, 

 both upon level and variously inclined roads. 



The route which will give the most general satisfaction consists 

 in following the valleys as much as possible and rising afterward by 

 gentle grades. This course traverses the cultivated lands, regions 

 studded with farmhouses and factories. The value of such a line 

 is much more considerable than that of a route by the ridges. The 

 water courses which flow down to the main valley are, it is true, 

 crossed where they are the largest and require works of large dimen- 

 sions, but also they are fewer in number. 



Intermediate Towns. Suppose that it is desired to form a 

 road between two distant towns, A and B, Fig. 6, and let us for the 

 present neglect altogether the consideration of the physical features 

 of the intervening country, assuming that it is equally favorable 

 whichever line we select. Now at first sight, it would appear that 

 under such circumstances a perfectly straight line drawn from one 



town to the other would be 

 c 



TX the best that could be chos- 



s \ s en. On more careful exam- 



NX S ination however, of the lo- 



s x s cality, we may find that 



^N there is a third town, C, 



B situated somewhat on one 

 side of the straight line 



which we have drawn from A to B ; and although our primary object 

 is to connect only the two latter, that it would nevertheless be of 

 considerable service if the whole of the three towns were put into 

 mutual connection with each other. 



This may be effected in three different ways, any one of which 

 might, under the circumstances, be the best. In the first place, we 

 might, as originally suggested, form a straight road from A to B, 

 and in a similar manner two other straight roads from A to C, and 

 from B to C, and this would be the most perfect way of effecting the 

 object in view the distance between any of the two towns being 

 reduced to the least possible. It would, however, be attended with 



