8 BULLETIN 1279, U. S. DEPARTMENT OF AGRICULTURE 
cent, were surfaced. Thus, while 789,915 miles had been added to 
our total highway mileage during the 17 years from 1904 to 1922, 
only 234,230 miles had been added to our surfaced mileage during 
the same period. In other words the mileage added to our highways 
was three and one-third times as great as the mileage added to our 
surfaced roads. The actual amount of highway improvement which 
was accomplished during these years, however, is much greater than 
the above figures would seem to indicate. A large mileage of low- 
type roads built during the period has been replaced with types more 
suitable to the present traffic requirements. Light and narrow 
bridges have been replaced with wider and more substantial structures. 
Old, narrow roads have been widened and straightened. In 1904 the 
highest type of surfacing found on our rural roads was water-bound 
macadam. At the beginning of 1922 a total of 25,610 miles of our rural 
roads were improved with high-type pavements. 
But even when full account is taken of all these improvements and 
betterments it is still clearly evident that our highway improvements 
have not kept pace with the increase in the traffic on our highways. 
In 1904 our highway traffic was almost entirely horse drawn. Prior 
to 1904 not more than 40,000 motor cars had been manufactured in 
the United States. A single factorv now produces more cars in a 
single week. The wholesale value of all motor cars manufactured in 
1904 was only $30,864,616, while in 1922 the wholesale value of the 
motor cars and trucks, as given by the National Automobile Chamber 
of Commerce, amounted to $1,789,638,365, or nearly double our total 
expenditure of $898,352,307 during the same year for construction, 
maintenance, engineering, and administration of our rural roads. 
During the registration year 1922 there were registered 12,238,375 
passenger cars and trucks. From such data as are available in regard 
to gasoline consumption it may be estimated that the average distance 
travelled by the typical motor vehicle is about 4,000 miles annually, 
making a total annual traffic of some 48,000,000,000 vehicle-miles on 
our public roads and streets. Our total highway expenditures during 
1922 were therefore at the rate of approximately 1.9 cents per motor 
vehicle-mile or slightly more than an average of $73 per motor car. 
During the year 1921 a total of 41,171.7 miles were improved with 
some form oi surfacing, while 34,456.3 miles were thus improved 
during 1922. While a smaller mileage was improved in 1922 than in 
the year 1921 the decrease was confined almost entirely to the sand- 
clay and gravel types which formed 70 per cent of the total mileage 
built in 1921, but only 64 per cent of the mileage built in 1922. 
In 1921 the mileage of surfaced roads built included 7,010.2 miles 
of sand-clay, 22,008.6 miles of gravel, 3,070.1 miles of waterbound 
macadam, 993.8 miles of surface-treated macadam, 1,349.2 miles of 
bituminous macadam, 208.5 miles of sheet asphalt, 1,022.6 miles of 
bituminous concrete, 4,805.4 miles of Portland cement concrete, 335.8 
miles of brick, and 367.5 miles of miscellaneous types, such as shell, 
cinder, etc. In addition to this surfacing 7,018.7 miles of earth roads 
were built to a definite grade and provided -with permanent drainage 
structures, while a certain amount of grading and drainage work 
other than ordinary maintenance was done on an additional 61,885.7 
miles of earth roads. Construction work of some kind was therefore 
done on 110,976.1 miles of rural roads during the year 1921. 
