Home >> Textbook-on-roads-and-pavements-1908 >> Abrasion Test to Street Railway Track >> Length of Road

Length of Road

value, saving, distance, traffic, transportation and proportional

LENGTH OF ROAD.

Changes in the length of a road affect all portions of the traffic in the same manner, and the expenditure of power and loss or gain in time occasioned by them are in general directly proportional to their amounts.

The value of any considerable saving in length may usually be considered as equal to the same percentage of the whole cost of conducting the traffic that the saving in distance is of the whole length. If, therefore, a rough estimate may be made of the annual traffic to be expected upon a given line of road and of the cost of carrying the traffic, this cost divided by the length in miles through which the traffic is moved will give the annual interest upon the sum that may reasonably be expended in shortening the road one mile, or upon the value of a saving of a mile in distance; or dividing by the number of feet of distance will give the value of saving one foot.

It is to be noted, however, that the cost of the work of transportation is not necessarily proportional to the amount of work done, and consequently this method would not be strictly accurate even were the data as to traffic and costs readily obtainable. An estimate of this character at best amounts to only a rough guess, but it may often be of use as an aid to the judgment in deciding upon the value of a proposed improvement involving a considerable change of length in a road.

Where the road is so situated and the saving in distance proposed is such that it would enable teams to make an additional trip per day in the hauling of freight, the difference in cost of transportation is quite tangible and readily estimated; but where the traffic is of a more indefinite nature, or the saving proposed insufficient to admit of additional trips, the value of the difference of length depends upon the value to other work of the small portions of time of men and teams which may be saved by the shorter route — a value which exists, but is difficult to estimate.

There is also a value in the saving of distance due to the advantage to the community of bringing various points closer together, such as bringing two towns into closer relations or bringing country property nearer to markets. The method of considering the cost as proportional to the work done will therefore probably give a fair idea of the actual economy in any saving in the work of transportation.

The value of reducing distance varies with the character of the road surface. • As the cost of transpor tation is less over a smooth than over a rough surface, on account of the lighter traction, the value of reduc ing distance is also less on the smooth surface.

The value of saving distance also is greater on a road where the ruling gradients are steep than upon one with light gradients, because of the greater num ber of loads necessary to move the same traffic.

The cost of maintenance of a road varies with its length, and under similar conditions may be con sidered, like the cost of transportation, to be directly proportional to the length of road.

The saving in cost of maintenance from decreasing distance must of course be added to that in cost of transportation in order to find the actual value of a change of length.

The value of straightness for a country road is fre quently very much overrated. Considerable devia tions from the straight line may often be made with but slight increase in length, and there seems to be no good reason for insisting upon absolute straightness. The error is commonly made of sacrificing grade and expense in construction to the idea of straightness without the attainment of any considerable saving in length.

It involves in many cases the injury of the beauty of the road and of the landscape, with no compensating economic advantages.