Book II. DIRECTION OF ROADS. 515 



331 1. All crossings, intersections, and abuttings of roads, should be made at right angles, 

 for the obvious reason of facilitating the turning from one road to the other, or the more 

 speedily crossing. Where roads cross each other obliquely, or where one road abuts oa 

 another at an acute angle, turning in, or crossing, can only be conveniently performed in 

 one direction. 



33 1 2. In laying out a road over a hill or mountain of angular figure and considerable 

 height, much practical skill as well as science are requisite. In order to preserve a 

 moderate inclination, or such a one as will admit of the descent of carriages without 

 locking their wheels, a much longer line will be required than the arc of the mountain. 

 In reaching the summit or highest part to be passed over, the line must be extended by 

 winding or zig-zagging it along the sides, so as never to exceed the maximum degree of 

 steepness. This may occasion a very awkward appearance in a ground plan, but it is 

 unavoidable in immense works. If a hill, 50 feet in perpendicular height ^Jig. 434.), 



434 h 



has an arc (a, b, c), or would require 150 feet of road (a, b, c) to go over its summit in 

 a straight line, then to pass over the same hill on a road rising at the rate of two inches 

 in six feet (the slope of the Simplon road], would require a length of 600 feet. If this 

 length were extended in a straight line (<Z, b, e) on each side, it would require an 

 enormous mound, and an immense expense ; but by being conducted in a winding 

 direction {b), up the hill on one side, and down the other, the same end is gained at a 

 moderate cost. Such works shew the wonderful power and ingenuity of man and 

 perhaps no example exists where this is so displayed in road-making as in the case of the 

 Simplon. 



3313. In laying out a road towards a river, stream, ravine, or any place requiring a 

 bridge or embankment, an obvious advantage results from approaching them at right 

 angles ; and the same will apply in regard to any part requiring tunnelling or crossing 

 by an aqueduct, &c. 



3314. In tracing out loinding railroads, or such carriage roads as are only to be 

 metalled in the horse track and paths of the wheels, some management is necessary in the 

 case of quick bends. Where the line is straight, the horse path ought to be exactly in 

 the middle between the wheel tracks. But, where the road winds, and most especially 

 at a quick bend, the horse track ought ever to incline toward the outer side of the curve; 

 by which the wheels will be uniformly kept on the middles of the supports prepared for 

 them. Hence, it is advisable to dig the trench for the horse path (Jig. 433 a.}, first ; and 

 to draw a carriage for which the road is intended, with the horses walking in this middle 

 trench : thus marking out, by the impressions of the wheels, the precise middle lines of 

 the outer trenches, in every part of the road, from end to end. 



3315. The directions of roads through an extendve estate, cannot be determined on 

 without having in contemplation the other fundamental improvements, such as the 

 situations of villages, farmeries, mills, or other objects ; and these artificial improvements 

 must be taken in connection with the natural surface, soil, materials, waters, &c. ; the 

 probable system of agriculture that will be pursued, and the external intercourse. A 

 hilly country under aration, will evidently require more roads than if chiefly under 

 pasture ; and, indeed, other circumstances the same, a country abounding in hills and 

 valleys, requires many more roads than one of a more even surface. The roads in such 

 a country are also more expensive, on account of the bridges, and extra work at their 

 abutments. On an estate composed of gentle hills chiefly intended for arable or con- 

 vertible husbandry, the best situation for the roads will generally be found about half 

 way between the bottoms and highest surfaces. By this means the labor of carting up 

 the produce from the fields below the road, and carting up the dung to the fields above 

 it, is evidently much less than if the road were either entirely on the highest ground 

 or the lowest. Bridges over the brooks or open ditches necessary for drainage in valleys, 

 are also rendered less frequent. 



3316. Accurate sections of the rises and falls of the natural surface on which a road 

 is to be formed should always be taken before the line is finally determined on. As the 

 figure of an exact section of this sort on any ordinary scale, would convey no data 

 suflBciently accurate for execution, it is usual to adopt one scale for the length, and 

 another for the rises and falls of the road, and to mark the latter with the dimensions as 

 taken on the survey. 



LI 2 



