The twice-a-week Twin Falls times. (Twin Falls, Idaho) 1916-1918, 1917-09-04


The minimum width to accommodate
safely two lines of average horse
drawn traffic is ii feet, and for auto
mobile traffic the width preferably
should be not less than IS feet though
a width of 16 feet is used frequently.
In order to maintain the Travelled way
to the required width and to afford
proper safeguards against accidents, it
is necessary to provide a shoulder not
less than three or four feet wide along
each side Of the roadway proper. The
shoulders may have a somewhat steep
er crown than the rest of the road
surface, but they should be sufficiently
fiat not to endanger traffic using them
and really should constitute an addi-
tiOnal width of roadway. This means
that the total width of roadway be-
tween side bitches never should be less
than 20 feet where horse-drawn traffic
predominates, and "A feet where any
considerable volume of automobile
traffic Is to be accommodated.
Where sharp curves occur in the
alignment it is desirable. though not
customary, to increase the width of
the Travelled way A vehicle being
drawn along a curved road tends to oc-
cupy an appreciably greater width
than where the road is straight, and
unless the width of the Travelled way is
increased correspondingly, this ten
dency contributes materially to the
hazards that invariably accompany
sharp curves. The minimum widths
given above should also be increased
on entertainments of any considerable
depth, so as to make maintenance
easier and at the same time diminish
the danger of accidents.
The width of right of way required
to provide all necessary area for the
roadway, slopes and bitches, varies
considerably with the nature Of the
topography.
Grades.
In designing public road one of the
most difficult problems to solve proper
| ly is the question of maximum allow
able grades. In deciding this question,
the advantages to be gained by reduc-
ing all of the sleeper grades on Il par
ticular road to given maximum
should be weighed against the addi-
tional cost which the reduction in
wolves.
The following data and suggestions
are intended to aid individual judg
ment, which necessarily must be the
prime factor in solving this important
problem:
1. The cost of average pleasure traf-
fic, horse-drawn and motor, is practi
cally unaffected by grades of not more
than or Z per cent (six or seven feet
rise per 100 feet, measured horizontal
ly), provided the conditions are such
that it is unnecessary to apply the
brakes to vehicles when descending
the grades. But for traffic where loads
are as Important as speed, even very
light grades may be of considerable
disadvantage.
2. Increasing the steepness of a
grade decreases in three distinct ways
the load horse can haul: (a) for the
same character of surface, the required
tractive effort or pull per ton of load
is increased by about 20 pounds for
each per cent increase in grade, (b)
the possible pull the horse can exert is
decreased by an amount equal to the
effort required to lift his own weight
through the rise. This amount is ap-
proximately equal to one one-hun-
dredth of the horses weight for each
per cent increase in grade, (c) the eff
fective pull of the horse is reduced by
the change in the angle at which the
pull is applied.
3. The pull horse can exert on a
level road varies greatly with the in
dividual animal, and is affected by the
manner Of hitching and the skill of the
driver. The character of the road
surface also may have an important
influence by affecting the security of
the horses foothold.
Tests made by the office of public
roads and rural engineering Indicate
that, on a level road, average farm
horses unframed to the road can exert
steady pull for several consecutive
hours equivalent to from 0.08 to 0.1O
of their own weight without undue
/ fatigue, and that by resting at inter
walls of from 500 to 600 feet they can
exert a pull equivalent to about OBS
of their weight, provided the foothold
is good
4. The tests referred to above also
indicate that with a well-constructed
wagos the pull required TO move a
gross load of one ton over a level road
varies about as follows:
L Pounds
Loose sand road ...........................3 1E
Average dry earth road (varies
greatly .lbt
| Firm earth OF sand-clay road .........1 Os
| Average gravel road .................... 81
First-class gravel or macadam road. s.
In general, the Judgment should be
largely influenced, in fixing the maxi
mum grade, by the topography of the
! region which the road traverses. Ac
! cording to the best current practice