The river press. [volume] (Fort Benton, Mont.) 1880-current, 1912-07-10

I'M Nr'0ANo 0AAA4 I0AA&0 N1S 0VO&S NO i
DUST.
chimes owned in the United States, and
the number is increasing at a marvel
rate.
The fact that must give US concern
ts 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-
fc and that we are in the midst Of a
transition period which must eventual
~ revolutionize the science and art of
the road builder. The highway en-
9ineer Of today is called upon to ascer-
tain in what way the automobile in
lures 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
Gil of bridges and roads in 1775 he set
forth the principles Of construction
which, as modified and added to by
John l.. 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 a road ca
pable of withstanding the wea 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
the crushed stone would fill the voids
between the angular fragments and
when wet serve as a cement, thereby
making the road surface practically a
monolith. The iron shod horses and
the iron tired wheels passing over the
road from time to time were depended
upon to wear off a 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. It follows that the
road is soon stripped of its fine bind
ing material. exposing the upper OF
wearing course Of the stone. These
stones robbed Of the binding materia,
are soon loosened by the shear of the
driving wheels, leaving the road badly
raveled or d~isintegrated. 1t is, o.
course, apparent that the effects de
scribed are greatly intensified or
curves, where skidding Is most fire.
Quent.
Highway and mechanical engineer
have given much study to the action 0:
the automobile on the road surface
and many ingenious theories have beef
advanced. While 1t Is true that tn
slipping of the tire, skidding, shape o
the car body, suction Of the pneumatic
tires, all contribute to produce the eft
feet. the most conclusive experiment
seem to warrant the assertion that tn
great tractive force or shear exertet
by the driving wheels of motorcars i
the main factor of injury.
A series of tests conducted by tn
United States Office Of public roads II
1908 produced some interesting result
along this line. Cars Of various weight
and types were run over a measures
course at different rates of speed an
right angle photographs taken OF eac|
run. A sixty horsepower car strippe
for racing. weighing with its drive
and m%echanician about $500 pounds
was driven over this stretch of road a
rates OF speed varying from five to sis
ty miles per hour. the speed being II
creased five miles per hour for ear
trip over the road. Up to fifteen mile
an hour little or no effect was produce
on the road. but from twenty miles IL
hour the effect was striking with ea''
increase in speed. These demonStr'
tons proved that little or no effect