2 BULLETIN 220, U. S. DEPARTMENT OF AGRICULTURE. 



and at various other expositions and fairs. The models have also 

 been displayed on road trains at all important places along the route 

 of the Pennsylvania Railroad in the State of Pennsylvania and along 

 the entire system of the Southern Railroad, also along the St. Louis 

 & San Francisco Railroad, the Atlantic Coast Line, the Nashville, 

 Chattanooga & St. Louis Railroad, and the New York Central & 

 Hudson River Railroad. A comprehensive exhibit of these models, 

 illustrating all standard types of construction, has been installed at 

 the Panama-Pacific Exposition in San Francisco, Cal. 



The models, as a rule, are constructed on a scale of 1 inch to the 

 foot, so that each model is one-twelfth the size of the actual road 

 which it represents. Modifications of the methods of construction 

 may be necessary to meet local conditions. Advice and information 

 relating to road construction, maintenance, or improvement in any 

 section of the country may be obtained upon application to the 

 Director of the Office of Public Roads. 



The descriptions of the models are so arranged in this bulletin as to 

 present the historic development of road building. The Roman road 

 is described first, and then descriptions are given successively of the 

 French roads, after the ideas of the Romans and of Tresaguet, the 

 roads of MacAdam and Telford, and finally the various types of 

 modern construction. Among the latter are models showing brick, 

 concrete, asphalt-block, macadam, sand-clay, gravel, and earth roads. 

 There are other models showing the processes of maintenance, resur- 

 facing, and bituminous macadam construction by the mixing and 

 penetration methods. One model shows the various methods of 

 draining and strengthening unstable foundations, while another 

 shows a typical method of treating gravel or macadam roads to make 

 them dustless and to prevent their disintegration under automobile 

 traffic. Two models recently added to the series illustrate, respec- 

 tively, road location and roadside treatment. 



ROMAN ROADS. 



The Romans began building roads on a large scale more than 300 

 years before the Christian era. The Appian Way, one of the most 

 celebrated of their roads, was begun in 312 B. C, by Appius Claudius 

 Csecus. This road led from Rome to Capua, a distance of 142 Italian 

 miles. It was later continued to Brindisi, making the total distance 

 360 miles. Rome continued as a great road-building nation for 

 about 600 years, and fragments of some of its roads still remain. The 

 Appian Way is said to have been in good condition more than 800 

 years after its construction. 



The Roman construction was not uniform, though always extremely 

 massive. The general form of construction employed during the 



