Greene County herald. (Leakesville, Miss.) 1898-current, 1913-01-24

AN OILED MACADAM ROAD WITH MACHINE
TRAVELLING SIXTY MILES PER HOUR-NO
DUST
chimes owned in the United States, and
the number is increasing at a marvel
Gus rate.
The fact that must give US concern
is that the old methods of construction
which have stood every test for more
than 100 years are inadequate to meet
the conditions of this new form of traf
fic and that we are in the midst Of a
transition period which must eventual
ly revolutionize the science and art of
the road builder The highway en-
gineer of today is called upon to ascer-
tain in what way the automobile in
jures the road what is the exact cause
of the injury. and finally to devise an
adequate remedy.
When Tresaguet, the great French
engineer, made his report to the coun-
ell of bridges and roads in It's he set
forth the principles of construction
which. as modified and added to by.
John T. Macadam in the early part of
the nineteenth century, have proved
adequate until the twentieth century
These great road builders and their
successors sought to secure road ca
pable of withstanding the wear of iron
tired horse drawn vehicles, for the mo
tor driven vehicles had no place in
their philosophy They worked upon
the theory that the dust abraded from
fI< nod csfo
between the angular fragments and
when wet serve as a cement, thereby
making the road surface practically a
monoiith. The iron shod horses and
the iron tired wheels passing over the
road from time to time were depended
upon to wear off sufficient amount of
rock dust to replace that carried away
by wind and water. and this under the
action of moisture recemented. thereby
automatically renewing the bond of the
road surface.
The rubber tired wheels. moving at
excessive speed, fail to produce any
new dust from the rock, but the tre-
mendous shearing effect of the driving
wheels loosens this dust, and as the
body of the machine displaces a large
volume of air the DETECTED currents
carry the rock dust off the road, there
by effecting a permanent loss Of the all
essential binder. 1t follows that the
road is soon stripped of its fine bind
ing material, exposing the upper or
wearing course of the stone. These
stones robbed of the binding material
are soon Ioosened by the shear of the
driving wheels, leaving the road badly
raveled or disintegrated- 1t is. of
course, apparent that the effects de-
scribed are greatly intensified on
curves. where skidding is most fire.
quent.
Highway and mechanical engineers
have given much study to the action of
the automobile on the road surface.
and many ingenious theories have been
advanced While it is true that the
slipping Of the tire. skidding. shape of
the car body, suction Of the pneumatic
tires, all contribute to produce the eff
feet, the most conclusive experiments
seem to warrant the assertion that the
great tractive force or shear exerted
by the driving wheels Of mOtorcars Is
the main factor of injury.
q series of tests conducted by the
United States Office of public roads IN
1908 produced some interesting results
along this line. Cars of various weights
and types were run over measured
course at different rates of speed and
right angle photographs taken OF each
run. A sixty horsepower car stripped
for racing. weighing with its driver
and mechanician about $500 pounds.
was driven over this stretch Of road at
rates of speed varying from five to six
ty miles per hour. the speed being IN
creased Eve miles per hour for each
trip over the road. Up to fifteen miles
an hour little or no effect was produced
on the road. but from twenty miles an
hour the effect was striking with each
increase in speed. These demonstra-
tions proved that little orano effect s