The building of the Hudson River tunnels was probably one of the most
daring engineering feats ever accomplished. As is well known, the Hudson
River, for the length of Manhattan Island, is approximately a mile wide,
reducing in width at the Palisades north of Hoboken. In consequence of
the unusual geographical situation, all trunk lines and other transit
facilities in New Jersey terminate on the westerly shore of the Hudson,
and passengers were of necessity compelled to use ferries to reach New
York. A conservative estimate, which was confirmed by various counts,
indicates that, prior to the construction of the tubes, the annual
passenger traffic between New Jersey and New York was 125,000,000, and
to handle this great volume of traffic the transportation companies
assembled in the Hudson River a fleet of rapid ferry boats and
maintained them up to the highest and most modern standards. But this
very expeditious ferry service was not enough, and for many years there
was a demand for facilities for more rapid transportation of the
tremendous population residing in the suburban district of New Jersey
tributary to New York City. As far back as 1873, a company had been
organized to construct a tunnel under the river, but had met with
numerous and most discouraging difficulties and obstacles, so that it
was finally compelled to abandon the work, although it succeeded in
building a considerable length of structure. Efforts were made at
various times after that date to revive the work, with little or no
results. In 1902 it was resumed, however, and a few years later was
pushed to a successful end.
During the undertaking, more than 40,000 men were engaged in
air-pressure work and there were many thousand more who did not work
under air pressure. This vast army of men consisted of all nationalities
and all grades and conditions of labor. The skilled tunnel workmen are
men of character and ability, usually young, of good intelligence and
sound of body, without a streak of fear or cowardice in their makeup.
All of those characteristics are essential to under-water air-pressure
work.
As is quite generally known, air pressure and tunnel shields were used
in all of the under-water work. It might be well to here correct the
misconception which exists in the minds of many, that the use of air
pressure for such purposes is something comparatively new. This is not
the case. The use of air pressure was a very early invention, and it is
a matter of record that in 1830, Admiral Cochrane, afterwards Lord
Dundonald, was granted letters patent for the use of air pressure in
tunnel construction. The modern engineer has merely developed the art to
a high degree.
The method of construction used in the Hudson River tunnels has been
designated the “shield method.” In this type of construction, the
primary part of the tunnel structure consists of an iron shell, formed
of segmental rings, bolted together through inside flanges, and forming
a large articulated pipe or tube, circular in section. This iron shell
is put in place segmentally by means of a shield, an ingenious mechanism
which both protects the work under construction and assists in the
building of the iron shell.
[Illustration: THE NEW SHORT CUT TO NEW YORK