Book II. DIRECTION OF ROADS. 573 



3555. As precedents for roads through hilly countries, Telford {Minutes before the Committee cf the 

 House of Commons, S(c. 1819.), refers to those which he has lately made through the most difficult and pre- 

 cipitous districts of North Wales. " The longitudinal inclinations are in general less than one in thirty ; 

 in one instance for a considerable distance there was no avoiding one in twenty-two, and in another, for 

 about two hundred yards, one in seventeen; but in these two cases, the surface of the road-way being 

 made peculiarly smooth and hard, no inconvenience is experienced by wheeled carriages. On flat ground 

 the breadth of the road-way is thirty-two feet ; where there is side cutting not exceeding three feet, the 

 breadth is twenty-eight; and along any steep ground and precipices it is twenty-two; all clear within the 

 fences : the sides are protected by stone walls, breast and retaining walls and parapets ; great pains have 

 been bestowed on the cross drains, also the draining of the ground, and likewise in constructing firm and 

 substantial foundations for the metalled part of the roadway." 



3556. The road between Cnpel Cerig and Lord Penrhyn's slate quarries may also be adduced as an 

 example of a very perfect enclosed plane in which the ascent is accurately divided on the whole space 



3557. Cutting through low hills to obtain a level is recommended by some, who, as Paterson observes, 

 will argue, " that where the hill of ascent is not very long, it is better, in that case, to cut through it in a 

 straight line, and embank over the hollow ground on each side, than to wind along the foot of it. This, 

 however, should only be done where the cutting is very little indeed, and an embankment absolutely 

 necessary. Few people, except those who are well acquainted with the subject, are aware of the great 

 expense of cutting and embanking; and the more any one becomes acquainted with road-making, the 

 more, it may be presumed, will he endeavour to avoid those levels on the straight line that are obtained 

 only by cutting and embanking, and will either follow the level on the curved line round the hill, or, 

 where this is impracticable, will ascend the hill, and go over it by various windings, avoiding always abrupt 

 or sudden turnings." {Treatise, <^c. p. 15.) 



3558. All crossings, intersections, and abuttings of roads, should be made at right angles, 

 for the obvious purpose 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 on 

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

 one direction. 



3559. In laying out a road over a hill or mountain of angular figure and considerable 

 height, much practic*! skill, as w^ell as science, is 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 {fig. 538. ), 



has an arc (a, 6, 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 (rf, 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 show the wonderful power and ingenuity of man ; and 

 perhaps no example exists where this power is so strikingly displayed in road-making as 

 in the case of the Simplon. 



3560. In laying out a road towards a river, stream, raviw, 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. 



3561. In tracing out winding 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 tr^ch for the horse path (fig. 535. 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, ^e pre;ise middle lines of 

 the outer trenches, in every part of the road, from end to end, , .,. . ;_ ^ j^ 



3562. The directions of roads through an extensive estate cmnot be determined bi^ 

 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 agrici. ture that will be pursued, and the external intercourse. A 

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



