Investigations, made during the progress of the work to determine the
physical character of the silt and its action on the tunnels, suggested
the possibility that the use of pile supports might be inadvisable. This
view was confirmed by actual experience in the operation of the tunnels
of the Hudson Companies between Hoboken, N. J., and Morton Street,
Manhattan, which were opened to traffic in February, 1908. The stability
of these tunnels under traffic gave further assurance that supports were
unnecessary under the North River tunnels of the Pennsylvania Railroad
Company, and they were therefore dispensed with.

_Cross-Passages Between the Tunnels._--The Bergen Hill tunnels, the land
portions of the North River tunnels and the tunnels under Manhattan are
connected by cross-passages at intervals varying from 50 to 300 ft. As
it was the desire of the Management to provide every arrangement
possible to insure the safety of its passengers and employees and also
to provide for the convenience of inspection, the question of
establishing cross-passages between the tunnels under the rivers was
given most careful consideration. The conclusion was finally reached
that such passages as it was possible to construct between these tunnels
might increase instead of diminish the danger in case of accident. No
more cross-passages have therefore been constructed in the sub-river
sections, except in the East River, where there is a cross-passage and
pump chamber combined between each pair of tunnels about 750 ft. from
the Manhattan bulkhead line.


PROBABLE RESULTS OF THE IMPROVEMENTS.

In preceding pages reference has been made to the general objects of the