14 BULLETIN 136, U. S. DEPARTMENT OF AGRICULTURE. 
Instances are also known where concrete road surfaces have shown a 
very high percentage of annual wear. In other cases there is appar- 
ently no measurable wear. If the road surface is built with the 
proper mix of concrete and carefully placed, it apparently should 
last indefinitely and not rut. Some cleaning of the surface and 
patching of joints and small depressions will be necessary at all 
times, so that the maintenance can not be entirely neglected. 
The cost of repair and maintenance upon brick highways is very 
low. In most instances, where the construction is as nearly perfect 
as possible, almost no maintenance charges have resulted. Perfect 
construction, however, is seldom obtained.! It is not unusual to 
find depressions and points of wear in brick roads, but it is less com- 
mon than formerly. Brick roads are now usually constructed on a 
concrete foundation, with very carefully selected vitrified brick, and 
with the joints filled with cement mortar. Their annual maintenance 
costs, although low, are not on record with sufficient continuity to 
supply accurate data. 
It has not been customary for officials to face frankly the cost 
of maintenance and repair on bond-built highways at the time the 
bonds are issued and before construction begins. In fact, in the 
majority of cases where bonds have been issued by local authorities 
there has been no provision whatever for maintaining the roads when 
built. This is perhaps the gravest defect in the project of building 
highways by issuing bonds. The cost of all maintenance and repair 
over a series of years has ranged in the past from 6 to 10 per cent of 
the original cost of construction on the average and varies with the 
type of construction. Concrete roads and brick roads apparently 
are a marked exception to this rule. In future construction where 
the type of road is properly adapted to traffic and with careful main- 
tenance from the outset the percentage of repair and maintenance 
cost should be lower. 
THE BOND ISSUE. 
Sinking-fund bonds.—The majority of highway bonds now 
outstanding have been issued as straight terminable bonds to be 
retired by sinking funds. Many such bonds now run for excessive 
terms. Although the term varies from 10 to 40 years, the average 
is nearly 25 years.2, The fund to retire the bonds is accumulated by. 
annual installments paid by the taxpayers and is supposed to draw 
interest continuously and to accumulate a sufficient amount to dis- 
charge the debt at maturity. The interest which the sinking fund 
draws is usually from 1 to 2 per cent less than the interest paid for the 
Joan. Five per cent highway bonds are common with the sinking 
fund calculated to draw 34 per cent interest. Table 6 shows the 
annual payments to the sinking fund necessary to accumulate $1,000 
1 Cf. Bulletin 23 of the U. S. Department of Agriculture. 
2 Some issues—notably New York State—run 50 years. Cf. Appendices A and B, 
