PARK AND CEMETERY . 
396 
great many data. Local conditions, too, 
are very variable, and each engineer 
or road superintendent should work out 
this phase of the subject for himself. 
Suffice it to say that very few macadam 
roads in this country are maintained at 
after the permanent pavement was laid, 
and found to be about 5,000 vehicles 
per day. Probably this increased traffic 
was due in part to its better condition 
with a better pavement. 
The formation of dust is of course 
be higher — dust will no longer be tol- 
erated, and the frequent sprinklings of 
oil and constant repairs will be consid- 
ered a nuisance. The question then will 
arise, how much value is the old ma- 
cadam in constructing a practically per- 
MINERAL RUBBER PAVEMENT ON DRIVEWAY WITHOUT CURB. 
all. They are generally built and left 
to wear out. When the cost of main- 
tenance passes a certain amount, the 
macadam should be replaced with other 
road surfacing material. There may be 
conditions where the volume of traffic 
is so great that the question of main- 
tenance goes beyond a mere question of 
cost — it becomes an impossibility. I 
will allude to one case of this sort that 
occurred on one of our Chicago boule- 
vards. A portion of this boulevard 
was reconstructed in 1905 and paved 
with twelve inches of macadam with a 
granite top at a cost of $1.25 per square 
yard. During the year following its 
construction fully 10 per cent of its 
original cost (or 12.5 cents per square 
yard) was spent in its maintenance, be- 
sides the regular charges for cleaning 
and sprinkling. In its second season 
it had deteriorated so much that the 
attempt to maintain it as a macadam 
road was abandoned, and a contract was 
let for a permanent bituminous pave- 
ment. It would be reasonable to esti- 
mate it would have cost 25 cents per 
square yard, or 20 per cent of its origi- 
nal cost, to have it put back in its 
original condition and maintained it 
during the year. During this period 
the traffic on it was about 3,000 vehicles 
per day. A census was taken in 1909, 
closely allied to the wear on macadam 
surfaces. If the formation of dust is 
prevented, it would at first appear that 
wear would be stopped. That is not 
exactly the case, because the stone may 
be raveled up and ruts and depressions 
formed without much wear on the stone 
itself and without the formation of 
dust. If a dust-laying preparation is 
used it must supply enough' binding ma- 
terial to hold the stone together. If 
the stone is effectively bound together, 
no dust is formed except, the limited 
amount formed by attrition from the 
particles of stone itself. Dust layers 
are various, from water, with or with- 
out the addition of hj^groscopic chemi- 
cals, to oil and water emulsions and 
crude or prepared oils, tars, etc. All of 
these have their value in preserving the 
road, as various experiences show, but 
will not be further discussed, as this 
paper is addressed principally to the 
problem of utilizing macadam as the 
base for permanent bituminous pave- 
ments. 
There will come a time on every 
macadam sl^reet, boulevard or much 
traveled highway when none of the 
available methods of caring for the 
broken stone surfaces will suffice. If 
the actual cost is not too great, the 
standard of excellence demanded will 
manent pavement, and how best can it 
be utilized? 
In the beginning of this paper I gave 
two typical examples of cities with ma- 
cadam pavement amounting to 50 per 
cent of their respective total areas of 
paved streets. In each case the original 
average cost was approximately $1.00 
per square yard. 
By the time the determination is 
reached to resurface the macadam streets 
with some other paving material, the 
macadam would probably require a com- 
plete resurfacing with, say, four inches 
of new stone, to restore them to ap- 
proximately their original condition. 
Four inches of new macadam stone, 
well rolled and finished, would cost 
about 40 cents per square yard, 
leaving the present value of the old 
macadam without this resurfacing 60 
cents per square yard. The old ma- 
cadam will be thoroughly compacted 
under the traffic, but full of ruts and 
holes and with a considerable accumu- 
lation of dirt over the surface. There 
w'ill, perhaps, be at least 75 per cent 
of the original amount of stone still on 
the street. 
The cost of cleaning off the accumu- 
lation of dirt, spiking up and redressing 
the surface, and covering it with a 
sprinkling of new stone (not exceed- 
