152 AGRICULTURAL ENGINEERING 



increase of effort that larger loads require on lower grades. 

 It is of course desirable to keep the grade as low as possible, 

 but different localities have different standards for the maxi- 

 mum grade. This maximum varies from 10 per cent for 

 roads used but little, to 4 and 6 per cent for those on which 

 the traffic is heavy. 



The drag can be used to the best advantage following 

 ra'ns, when the soil is still moist. It then has a better 

 smoothing action and the earth scraped into the low places 

 is easily compacted. Roads which are dragged continu- 

 ously for a term of years become very dense and hard. 



QUESTIONS 



1. What is the mileage of earth roads in the United States? 



2. Why should earth roads be given careful attention? 



3. What are the two divisions of the subject of earth roads? 



4. Why is the drainage of earth roads important? 



5. How much slope should the crown of the road have toward the 

 side ditches? 



6. Is it important that the crown be of any particular shape or 

 form? 



7. What will be the result if the sides of the crown are given too 

 much slope? 



8. How should earth roads be maintained? 



9. What is a good width for a country earth road? 



10. What should be the maximum grade for earth roads? 



11. Explain the action of the road drag. 



