6 THE TESTING OF KOAD MATERIALS. 



can be executed with dispatch, and the results should be clear and 

 comprehensive. While it is necessary that the results should indicate 

 the wearing qualities of the materials in service, it is unnecessar}^ as 

 well as impracticable, that an attempt should be made to imitate the 

 exact conditions of service. Laboratory experiments have been 

 designed in various ways to reproduce the conditions that obtain in 

 practice, but they have failed for the obvious reason that the principal 

 element in such conditions is lapse of time, which renders quick 

 results impossible. 



It is apparent that no single material or class of materials will suit 

 all conditions of climate and traffic. To get the best results it is 

 necessary that the materials selected, as well as the methods of con- 

 struction, should be adapted to the special conditions of the road that 

 is to be built or maintained. This is not always practicable and is 

 often impossible. Much can be done, however, by means of labora- 

 tory tests to determine which of the available materials is best suited 

 for use, and this work constitutes the chief usefulness of the Road 

 Material Laboratory. A macadam road, when properly constructed, 

 o-ts from $4,000 to $10,000 a mile, and the cost of many other types 

 of road are greatly in excess of this. An error in the selection of a 

 material means an inferior road and occasionally complete failure. 

 Such an error, therefore, may cause a great loss of money to the com- 

 munity in which it occurs. 



No explanation is necessary of the second and third subdivisions of 

 the work, i. e., the development of new tests and the collection of cor- 

 n-lated data, which is similar in most respects to that of all testing 

 laboratories. 



The fourth subdivision or research work, including the development 

 of new materials, is of a most important character. New road mate- 

 rials are occasionally developed, and the methods for using old ones 

 arc constantly improving. It is most important to test and investigate 

 such materials and methods if the best results are to be derived from 

 them. Practically none of our rural towns or counties has the facili- 

 ties or means to carry on such investigations, and it is in these dis- 

 tricts that better roads are most needed. Kven when road building 

 is attempted materials and methods are frequently used which are 

 un.Miited to the conditions of climate and trallic and the result is failure. 



Probably the most difficult problem to solve for the betterment of 

 rural liiglnvay>. and one on which the Road Material Laboratory has 

 been at work for some time, exists in those sections of our country 

 where no hard materials are to be found from which roads can be con- 

 structed. Many of these districts are of very great extent, and have 

 only a clay soil on which and from which to build roads. The result 

 is that during a considerable portion of the year the roads are almost 

 impassable and are rarely good at any time. The Koad Material 



