34 IOWA DEPARTMENT OF AGRICULTURE. 



sible, so that the rainfall or melting snow will flow freely and quickly 

 into the gutters alongside. Probably the best shape for the cross sec- 

 tion of the earth road is an arc of a circle with a gradual fall from 

 the center to the sides of about 1 in 20, after the surface has been thor- 

 oughly rolled or compacted by traffic. (Fig. 12.) Such a surface can 

 be constructed and repaired with the road machine, and a roller can 

 be used upon it to good advantage. When the surface is not kept smooth 

 and compact the crown should be a little steeper than 1 in 20, but should 

 under no circumstances exceed 1 in 12. If the crown is too great, the 

 traffic will follow the middle of the road, and this will result in making 

 ruts and ridges which retard the prompt shedding of the water into the 

 side ditches. Too much crown is as detrimental as too little. 



CLEARING THE ROADWAY. 



Where new roads are to be built, all stumps, roots, vegetable matter, 

 rocks, etc., should be removed from the surface and the holes should 

 be filled in with suitable material, carefully and thoroughly tamped. In 

 forming a permanent embankment no perishable material should be used. 

 If suitable material is discovered in the subgrade, it should be removed 

 and replaced with good material which should be tamped or rolled until 

 smooth and compact. As stated above, the longitudinal grade should be 

 kept down to 3 or 4 per cent if possible and should, under no circum- 

 stances, except in mountainous regions, exceed 5 per cent; while that 

 from the center to the sides should be maintained at about 5 per cent. 

 After the roadbed has been brought to the required grade and crown, 

 a roller should be secured and used in consolidating the material. All 

 ruts or depressions discovered during the rolling should be leveled off 

 and rerolled. (Fig. 16.) 



WIDTH AND ELEVATION. 



The width of the traveled way will depend upon the requirements 

 of traffic. Sometimes 12 feet will suffice, but 18, 24 and 40 feet are the 

 usual widths for the various classes of country traffic. Where the road 

 is likely to be improved with brick, stone or gravel, sufficient width 

 should be provided for a hard road for winter use and a space alongside 

 for summer use. The right of way should be much wider than the trav- 

 eled way, in order to provide for widening when traffic requires it. 



In level countries where the natural drainage is poor it is very de- 

 sirable that roads should be elevated above the subgrade or surrounding 

 ground. For this purpose the required material may be secured by wid- 

 ening the side excavations or from cuttings on the line of the roadway 

 by means of road machines, elevating graders, or modern dumping 

 wagons. When the earth is brought up to the desired level it should be 

 thoroughly mixed by harrowing, then trimmed with a road machine, and 

 finally rolled with a road roller, the weight of which should be gradually 

 increased by ballast as the rolling progresses. During the rolling the 

 surface should be sprinkled with water if the character of the soil re- 

 quires such aid for its proper consolidation. The crown of the roadway 



