American Rural Highways

by T. R. Agg

New ideas are constantly being injected into the art of road building, but these are disseminated somewhat slowly, so that valuable devices and improvements in methods remain long unknown except to the comparatively few who have the means for informing themselves of all such developments.

It follows then that the logical system of conducting road improvement is through an agency of continuing personnel which will supervise the preparation of suitable plans and direct the construction in accordance with the most recent experience.

Road Plans.—The information shown on the plans prepared for road improvement varies somewhat with the design and with the ideas of the engineer as to what constitutes necessary information, but in general the plans show the existing road and the new construction contemplated in an amount of detail depending principally upon the character of the construction. Simple plans suffice for grade reduction or reshaping an earth road surface, while for the construction of paved roads, the plans must be worked out in considerable detail. The essential requirement is that there be given on the plans all information necessary to enable the construction to be carried out according to the intentions of the engineer, that all parts of the work fit together, that the culverts are of the proper size and located at the proper places, ditches drain properly, grades are reduced to the predetermined rate, that excavated material is utilized and that an exact record of the work done is retained. Plans are indispensable to economical road construction and the preparation of the plans is the work of the expert in road design, that is, the highway engineer.

Problem of Design.—The problem of road design is to prepare plans for a road improvement with the various details so correlated as to insure in the road constructed in accordance therewith the maximum of safety, convenience and economy to the users thereof. The degree to which the design will be effective will depend to a considerable extent upon the financial limitations imposed upon the engineer, but skill and effort on the plans will do a great deal to offset financial handicap and no pains should be spared in the preparation of the plans. Moreover, the plans must afford all of the information needed by the contractor in preparing a bid for the work.

Preliminary Investigation.—The first step in road improvement is to secure an adequate idea of the existing conditions on the road or roads involved. The detail to which this information need go will depend entirely upon the purpose of the preliminary investigation, for before a definite plan is prepared, it may be necessary to choose the best from among several available routes. For this purpose, it is not always necessary to make an actual instrument survey of the several routes. A hasty reconnaissance will usually be sufficient. This is made by walking or riding over the road and noting, in a suitable book or upon prepared blanks, the information needed. The items of information recorded will usually be as follows: distances, grades, type of soil on the road and nature of existing surface, character of drainage, location of bridges and culverts and the type of each with notes as to its condition, location of railway crossings and notes as to type, location of intersecting roads, farm entrances, and all similar features that have a bearing on the choice of routes. These data can be obtained in a comparatively short time by a skilled observer who may drive over the road in a motor car. Sometimes it may be desirable to make a more careful study of some certain sections of road and this may be done by waking over the section in question in order to make a more deliberate survey of the features to be considered than is possible when riding in a motor car.

Factors other than relative lengths of routes will obviously determine the cost of improvement and the comparative merits of the improved roads. Some special characteristic of a road, such as bad railroad crossings or a few bad hills, may eliminate a route, or availability of materials along a route may offset disadvantages of alignment or grade.

In special cases, complete surveys of routes may be required finally to select the best route, but these instances are few in number.

Road Surveys.—When a road has been definitely selected for improvement, a careful survey is made to furnish information for the preparation of the plans. This will consist of a transit survey and a level survey.

The transit survey is made by running a line between established corners following the recorded route of the road, or if no records are available or the road is irregular in alignment, by establishing arbitrary reference points and running a line along the center line of the existing road or parallel thereto. The topography is referenced to this line in such completeness that it can be reproduced on the plans. The level survey consists in taking levels on cross sections of the road at one hundred foot intervals, and oftener if there are abrupt changes in grade. Special level determinations are made at streams, railroad crossings, intersecting roads or lanes and wherever it appears some special features of the terrain should be recorded.

From the surveys and such other information as has been assembled relative to the project, a plan is prepared which embodies a design presumed to provide for an improvement in accordance with the best highway practice.