The Caldwell tribune. [volume] (Caldwell, Idaho Territory [Idaho]) 1883-1928, 1922-05-02
GRANT HIGHWAY
WILL TEST ALL
ROAD MATERIAL
Various Types of Con-
struction Will Be Used
On This Transconti-
mental Road.

(By J. E. Pennybacker, Former Chief
Economist, U. S. Bureau of Public
Roads.)
The Grant Highway, already as
Stunning importance as one of the
great transcontinental routes, will in
clude excellent examples of every
modern type of pavement recognized
by the science Of modern highway
engineering. These types will include
the famous BLACK base or flexible
type of highway, of which large
mileage has been completed in Ore
gon, the plain Portland cement con-
crete highway, which has been built
in illinois and Iowa, some brick
stretches at intervals, and large
stretches of maeadam, gravel and
earth, much of which will have as
phaltic material applied to the sur
face. A feature interesting both to
engineers and taxpayers in the build
ing of this great highway will be the
comparison of service and ultimate
cost that will develop between the
flexible BLACK base" surface and the
rigid Portland cement concrete pave
ments.
Highway engineers are divided into
two schools, one advocating the flex-
IDLE or BLACK base" pavement to re-
sist impact and the other advocating
rigidity to accomplish the same pur-
pose. The BLACK base" pavement
consists of an underlying course of
crushed stone, Stag or gravel, seldom
exceeding four or five inches in thick
ness, cemented together with asphalt.
1t is contended that the resultant mix
ture IS waterproof and so flexible that
instead of shattering under heavy i'm
pact it seeks closer contact with the
subgrade or underlying earth and
thereby secures the maximum sup
porting value of the earth itself. The
rigid Portland cement concrete type
consists of slab of Portland cement
concrete, in some cases reinforced
with metal. Originally this type of
pavement was laid five and six inches
thick. Recent practice calls for slabs
from seven to ten inches thick REIN
forced with metal 4
1t is the right of taxpayers to have
these engineering problems worked
out with exceeding care and also to
force as keen a competition as posi-
BILE between competitive types. Thos.
II. Macdonald, chief of the U. S. bu-
reau of public roads, discussing the
matter of competition of types of
pavement, recently said: Granting
that the preparation of the road-bed
has been properly done, many kinds
of road surfaces will give excellent
service. The element of time is i'm
portant. There are so many miles of
roads to be constructed and their cost
will be SO enormous that the most
careful and detailed study of each road
project must be made to provide, at
the lowest possible cost, roads which
will give satisfactory service and
which can be maintained without un-
due depreciation under the traffic
which is to use them. Many times
the question has been asked the bu-
reau, What type of road is bestf
The answer is always the same
There is no one best kind or type of
road surface"
A recent statement issued by the
officials Of the bureau expresses this
thought in the following language:
1T is the policy of this bureau to con-
slider the conditions on each individ-
ual federal aid project, as there are
elements, such as subgrade, drainage
and present and prospective traffic,
which vitality affect the determination
of the standards of construction to be
used. That Is, there must be q care
full analysis both of the engineering
and economic conditions for each par
ticular case to determine the kinds OF
materials that can be used success
fully, and, after these facts are de-
termined, then the various types OF
construction which can be used eco
nomically should be brought into COM
petition to secure the best possible re-
suits. Competition between different
types of material should be maintain
ed and selection made to fit traffic re-
quirements in each case. The bureau
Continued nm asst Paael