28 HIGHWAY CONSTRUCTION 



ing them. Such is not the case. The animal force must be sufficient, 

 either in power or number, to draw the load over the level portions 

 and up the steepest inclines of the road, and in practice no reduction 

 in the number of horses can be made to correspond with the decreased 

 power required in descending the inclines. 



The popular theory that a gentle undulating road is less fatiguing 

 to horses than one which is perfectly level is erroneous. The asser- 

 tion that the alternations of ascent, descent, and levels call into play 

 different muscles, allowing some to rest while others are exerted, 

 and thus relieving each in turn, is demonstrably false, and con- 

 tradicted by the anatomical structure of the horse. Since this doc- 

 trine is a mere popular error, it should be utterly rejected, not only 

 because false in itself, but still more because it encourages the building 

 of undulating roads, and this increases the labor and cost of trans- 

 portation upon them. 



Level Stretches. On long ascents it is generally recom- 

 mended to introduce level or nearly level stretches at frequent inter- 

 vals in order to rest the animals. These are objectionable when 

 they cause loss of height, and animals will be more rested by halting 

 and unharnessing for half an hour than by travelling over a level 

 portion. The only case which justifies the introduction of levels 

 into an ascending road is where such levels will advance the road 

 towards its objective point; where this is the case there will be no 

 loss of either length or height, and it will simply be exchanging a 

 level road below for a level road above. 



Establishing the Grade. When the profile of a proposed 

 route has been made, a grade line is drawn upon it (usually in red) in 

 such a manner as to follow its general slope, but to average its irregular 

 elevation and depressions. 



If the ratio between the whole distance and the height of the line 

 is less than the maximum grade intended to be used, this line will be 

 satisfactory; but if it be found steeper, the cuttings or the length 

 of the line will have to be increased ; the latter is generally preferable. 



The apex or meeting point of all curves should be rounded off 

 by a vertical curve, as shown in Fig. 8, thus slightly changing the 

 grade at and near the point of intersection. A vertical curve rarely- 

 need extend more than 200 feet each way from that point. 



