A NATIONAL PLAN FOR AMERICAN FORESTRY 



271 



ward trend can be explained by preservative treatments and mechani- 

 cal protection of ties, and by decline in railroad construction. 



According to the records of the American Railway Engineering 

 Association, the average figure for renewals on the principal railroads 

 was 261 ties per mile for the 5-year period ending with 1915. In 1929 

 the 5-year average was 180 ties per mile, marking a steady decline of 

 31 percent. It is not improbable that this trend may continue until, 

 possibly by 1945 or 1950, the average annual requirement for replace- 

 ments is less than 125 ties per mile. Requirements for several 

 railroads are already below that figure. 



The railroad mileage in the United States has decreased since 1916, 

 as shown in table 10, but the total track mileage, including supple- 

 mentary trackage, sidings, and yards, has increased about 3,000 miles 

 per year since 1924. 



TABLE 9. Recorded purchase of crossties, 190629 



TABLE 10. Steam railway mileage in the United States, by 2-year periods, 1900-28 1 



1 From Interstate Commerce Commission reports. 



It is impossible to say how long this rate of increase will continue, 

 but the encroachments of automobiles, busses, and trucks upon 

 rail business and the increasing use of trucks and busses by the 

 railroads themselves make it very probable that new construction, 

 together with the annual number of ties required for it, is due for 

 an eventual or early decline. 



Should tie renewals drop to 120 per mile annually by 1950, then 

 51 million ties will be required in that year to maintain the 1928 

 trackage of 427,750 miles. If the present increase of 3,000 miles 



