Evening star. [volume] (Washington, D.C.) 1854-1972, 1931-03-29
In the Motor World
BY @. ADAMS HOWARD.

GALES in the automobile in
dustry are picking up. True,
they are far from approach
ing the banner years in the
automotiye field, and are still
behind this period of last year,
which was before the national de-
preston in business became
greatly felt.
A distinct gain is being shown,
however, and predictions made at
the automobile shows that a real
boon would be experienced by the
end of the Spring months does not
seem unlikely.
Factory Auto Sales.
February factory sales of auto
mobiles in the United States, as
reported to the Bureau of Census,
consisted of 219,897 vehicles, of
which 181, 735 were passenger cars,
1888 trucks and 529 taxicabs, as
compared with 1851 vehicles in
January, 1881; 330,414 vehicles in
February, 1880, and 466,418 in
February, 1929.
Sales in Canada, reported by
Dominion Bureau of Statistics,
3 were 9,871 total vehicles for Feb
ruary, 1881, compared with 6,496
for January of the same year;
1888 for February, 1880, and 81
287 for February, 1929.
In the United States the sales
for the month just passed are the
highest since September, 1880,
when the sales we're 220,649. Fig
ures for October, November and
December of that year were 154,-
Z 401, 135,754 and 155, 701, respec-
= lively.
From the above a gradual but
steady increase can be seen.
Effect of Wheel Loads.
Thomas H. Macdonald, chief of
the Bureau of Public Roads, ap-
pearing at the invitation of the
Interstate Commerce Commission
ut the hearings held by that body
on the coordination of rail and
motor transport, docket % 400, in
this city on March 4 and 5, pre-
Sented evidence of the effect of
variation of vehicular wheel loads
and impact on the design of rigid
pavements as disclosed by inveSti-
cations of the bureau.
Mr.. MacDonald's testimony was
summarized in a table listing the
essential factors of road design
corresponding to the wheel loads
of several sizes and types of
vehicles and showing the edge
and center of concrete road slab
required for each condition.
1t was shown by these data that
the average thickness of slab re-
Quired for the support of the
wheel load and impact Of a 7R-
ton truck equipped with pneu-
matte tires and operated at a
speed of 80 miles an hour over a
surface of smoothness equal to
that of a particular street in the
National Capital taken as STAN
dard, would be approximately IS
per cent greater than the mini
mum practicable thickness that
would be required for traffic of
7-paSsenger automobiles.
Use of cushion and solid tires
on the same 7h-ton truck oper-
ated at 20 miles an hour over a
surface Of the same SmoothnesS
would neceSsitate greater thick
ness Of slab, averaging for cushion
tires 81 per cent and for solid
tires a per cent greater than the
minimum practicable thickness
required for 7-passenger auto
mobiles.
Reaction of so.
The slab designs presented in
the table for each of the types of
vehicles considered were based
upon the assumption of a modulus
of subgrade reaction of so, CORE
spending to a relatively soft sub
grade, and upon areas of contact
Of tires with the pavement such
as are actually obtained with
normal tire equipment for each
size Of vehicle.
The impact forces correspond
ing to the static wheel loads of
each class of vehicle under the
assumed conditions of operation
were taken at values actually
measured by the bureau in its in
vestigations. While the designs
represented in the table submitted
we're based upon assumed speeds
of 80 miles an hour for pneumatic
tired equipment and 90 miles an
hour for cushion and solid tired
vehicles, Mr.. Macdonald pointed
out that there is practically no
increase in the impact delivered by
pneumatic tires for speeds be-
tween 80 and IS miles an hour,
and that the cushion and solid
tired vehicles cannot be economi-
cally operated at speeds materially
greater than 90 miles an hour.
Mr. Macdonald emphasized the
fact that the controlling vehicular
factor in the design of roads is
not the gross load of the vehicle.
but the maximum wheel load and
the corresponding impact under
the most severe operating condi-
tons legally permissible. He
stated that the bureau definitely
favors the limitation of wheel
loads IT, not more than 5000
pounds and believes that the use
of solid tires should be strongly
discouraged.
Bridge Completion.
Stretching across the Hudson
River from mammoth pillars Of
steel and concrete, the worlds
longest cyfcpaa ci0Y1 hr{6un {S rear-