HIGHWAY COST KEEPING. 11 
UNITS OF MEASUREMENT. 
Care should be taken in selecting the units on which to collect cost 
data. Too many and varied units will make the system cumbersome 
and expensive, while too few may impair its value seriously. Fur- 
thermore, the units of measurement adopted for any cost-keeping 
system or project must be definite, expressive, readily obtainable, 
and familiar. Thus, for example, the ton and the cubic yard as 
applied to broken stone are definite units and afford a ready and 
accurate comparison, but the square yard when applied to a finished 
macadam road is indefinite until additional information as to the 
depth of the material is available. Similarly, many units, such as 
wheelbarrow, wagon, truck, or carload, while often convenient units 
of count in the field, are indefinite and always should be reduced to 
definite comparable units, such as cubic yard or ton. 
The units selected must, so far as possible, be expressive of definite 
operations. Thus, while in engineering construction the cubic yard 
is a very common unit upon which contract prices are based, it fre- 
quently is a very uncertain unit of performance, as it is a composite 
of other units. For example, in rock excavation there are involved 
the following operations: (1) Drilling, (2) blasting, (3) breaking large 
chunks, (4) loading into carts, wagons, cars, or the like, (5) trans- 
porting, (6) dumping. 
The important item of drilling depends largely on the necessary 
spacing of the drill holes, which varies in the different kinds of rock 
and in different kinds of excavation. Clearly, then, the linear foot 
of drill holes is the unit for measuring the output of the drillers, and 
not the cubic yard. Transporting the rock is largely a function of 
distance; hence the unit of transportation cost should be the ton or 
yard carried 100 feet or 1 mile, and not the cubic yard without the 
factor of distance. 
The units must be obtainable readily or the cost of collecting the 
necessary data will be too high. Thus, for example, to obtain the 
exact cubic yardage and the distance it was moved in preparing the 
subgrade for a macadam road with a road machine would be not only 
difficult, but expensive. Hence for this class of work the readily 
obtainable, though less definite, unit of the square yard usually is 
adopted. 
That the full value of the cost-keeping system may be realized, 
the units in which the data are expressed must be familiar to those 
charged with their collection as well as to those who are to profit 
from their use. Thus, the cubic meter is as definite a unit for meas- 
uring earthwork and generally as readily obtainable as the cubic 
yard, but to the average roadman it has little or no meaning until 
translated into the terms in which he is accustomed to think. If 
