MOTOR TRANSPORTATION FOR RURAL DISTRICTS 13 
average yearly interest. In this formula A represents the estimated 
life of the truck in years under actual operating conditions; B repre- 
sents the original investment; and C represents the rate of interest. 
To illustrate the use of this formula let it be assumed that a truck is 
purchased for $3000 which the operator estimates will last for 4 years 
under his operating conditions. Six per cent may be considered a 
fair rate of interest. Inserting the necessary values in the equation 
= x y 
given above, we have: rin x 6 Se000 — $112.50 (average yearly 
interest). The use of such a formula makes it possible to estimate, 
with a reasonable degree of accuracy, the amount which should be 
set aside each year as interest on the investment. 
REPAIRS. 
The regular repair bill, when coupled with the annual cost of over- 
hauling, is often a serious one. The experience of motor truck opera- 
tors in various sections of the country show that this is an important 
item of expense. Naturally it is impossible to make an advance 
estimate of these costs with any reasonable degree of accuracy. The 
annual repair bill will bear a practical relation to operating condi- 
tions. Where care is used in handling the truck, the cost of repairs 
will be much less than where no attempt is made to exercise reasonable 
supervision over operation. The cost of repairs increases with the 
age of the truck. Those operators who have purchased used equip- 
ment have found their repair bills relatively higher. Repairs during 
the first year of life of the new truck are not a very serious considera- 
tion. When the motor truck is in more or less continuous use through- 
out the year, it is usually laid up once each year and given a complete 
overhauling. The cost of this overhauling depends on the age of the 
truck, the care which it has received, and its size. Data collected by 
the Bureau of Markets show annual costs of overhauling ranging from 
about $100 to as high as $800 or $900. Those truck operators who 
make it a point to keep their trucks in a constant state of repair have 
relatively small charges to meet for annual overhauling. Those who 
operate their trucks as long as possible with no regular repairs must 
often face an extremely heavy charge for overhauling at the end of 
each year. 
TIRES. 
Tire cost is another heavy item of expense. ‘This item varies directly 
with the use of the truck. Road conditions are a prime consideration 
in determining tire cost per mile of operation. It is often found that 
there is a very wide variation in tire cost of different trucks operating 
with varying loads and under changing conditions. Data in the pos- 
session of the Bureau of Markets show a range of tire costs of from 
one cent to four cents per mile where solid tires are used. ‘These 
figures cover a large number of trucks of different sizes, operating with 
