394 
Roads and Highways : their History, 
showing the comparative disadvantage of hilly roads from 
gradients of 1 in 600 up to 1 in 7, both for light and heavy- 
traffic, from which it appears that hills act more disadvan- 
tageously on the heavy than on the light traffic. From these 
Tables the equivalent length of road, so far as the mechanical 
power required for the traction is concerned, with an inclina- 
tion of 1 in 30, compared with a level one, is as 1 is to 2*7 
miles for a heavy load ; and for a light load as 1 is to 1*6. 
With a road having an inclination of 1 in 12 the proportions 
are as 1 is to 5*2 and 2'5 for heavy and light traffic respectively. 
In an uneven country, hills cannot be altogether avoided ; nor 
is it necessary that the expense of forming a dead-level should 
be resorted to, as the occasional change of exertion from one set 
of muscles to another affords a certain amount of rest to the 
horses, while the inclination of the road assists materially in 
the escape of the rainfall. If roads with an inclination are so 
neglected as to allow the formation of ruts, these form channels 
for conveying this water away, which otherwise would remain 
stagnant, and render the surface soft and yielding. Mr. Walker, 
in his evidence before the Parliamentary Committee on Roads, 
stated that he considered an inclination of 1 in 80 was desirable 
for this purpose. 
The actual inclination must depend upon local circumstances, 
which alone can form a guide as to the most expedient gradient 
to be adopted. As a rule, it may be taken that the angle of 
inclination should correspond with the angle of repose, or that 
at which a carriage would not quite roll down by its own 
gravity. This, on a good road, is about 1°*25', or a rise of 1 foot 
in every 40 feet horizontal. At this inclination it is safe for a 
horse to trot downwards with a light carriage at the rate of 
12 miles an hour, and it is not sufficient to impede his speed in 
rising. An inclination of 1 in 24 should never be exceeded, but 
the nearer the approach of the gradient to the angle of repose, 
the more satisfactory is the result. 
Inclinations of 1 in 12 are not uncommon on some of our 
main roads, and Telford found many of the roads in Wales with 
gradients of 1 in 6, which he reduced on his new line to 1 in 
20. In Law's ' Treatise on Engineering,' the annexpd Table 
of the angles of resistance on roads, composed of various 
materials, is given, and is calculated from experiments made 
by Sir John MacNeill. 
An important point for consideration in the management of 
roads is the traction or actual power required to overcome fric- 
tion and other resistance in moving the vehicles. This varies 
considerably with the condition of the road, the class of vehicle, 
and the rate of speed. Speaking generally, it may be said that 
