HIGHWAY CONSTRUCTION IN MASSACHUSETTS. 79 



tied policy of the commission to reduce all grades to a maximum 

 of five feet in one hundred called a five-per-cent grade. After 

 courses and distances are plotted, and the necessary data obtained 

 for determining the quantity of the various materials used in the 

 construction of a road, a conference is held between the peti- 

 tioners and the State commissioners, in order to ascertain if a 

 contract for the construction of the road is to be made by the 

 municipality, and, if so, at what price it is to be done. In case 

 the city or town authorities are unwilling to contract for the 

 work upon the prices agreed, the commission advertises the same, 

 and it is let to the lowest responsible bidder, subject to the ap- 

 proval of the Governor and Council. It is the custom in award- 

 ing competitive contracts to require the contractor to furnish 

 bonds : one insuring a faithful completion of the work ; the other 

 to safeguard the interests of the town or city in case damage 

 results from accidents during the building of the way. Upon the 

 contract being made and a notification being received that the 

 municipality or contractor is ready to proceed with the work, the 

 commission appoints a resident engineer, who has personal charge 

 of the work of construction, subject only to the supervision of 

 the chief engineer. 



Now comes the period of actual construction, and the first step 

 in advance is the excavation and filling the road to the required 

 subgrade. In general the subgrade is about nine inches below 

 the finished grade ; but the extent of excavation differs widely in 

 actual practice, owing to the different treatment necessary as 

 determined by the varying character of the ground. The sub- 

 grade established and rolled, broken stone is then added to a 

 depth of six inches, the fragments varying in size from one and 

 a quarter to two and a quarter inches in their longest dimen- 

 sion. This is then rolled with a steam roller until thoroughly 

 compacted (Plate I). A second layer of broken stone, three 

 inches thick, is next spread upon the road, the pieces ranging in 

 size from one half to one and a quarter inch. This is then 

 rolled as before, and a finishing coating of screenings, put 

 through a half-inch mesh, is then added to a depth of half an 

 inch. Water is now turned on until the broken stone is well wet 

 down, when the final rolling is done, and the surface becomes 

 firmly and smoothly knit together (Plate II). In the foreground 

 of this picture the second layer of broken stone is seen. The main 

 part of the road is in its completed state, having just been com- 

 pacted with the steam roller. Some modifications are made in 

 these steps of the process, depending upon the quality of the 

 stone used and the amount and kind of travel to which the road 

 is to be subjected. As pointed out by Macadam, it is not wise to 

 place a layer of broken stone directly upon a subgrade of granite 



