York City near Christopher Street, was partly constructed, but the work
was abandoned for financial reasons. Then plans for a great suspension
bridge, to enable all the railroads reaching the west shore of the North
River to enter the city at the foot of 23d Street, were carefully
worked out by the North River Bridge Company. The Pennsylvania Railroad
Company gave this project its support by agreeing to pay its _pro rata_
share for the use of the bridge; but the other railroads declined to
participate, and the execution of this plan was not undertaken.

New operating conditions, resulting from the application of electric
traction to the movement of heavy railroad trains, which had been used
initially in tunnels by the Baltimore and Ohio Railroad and was
subsequently studied and adopted by railroads in Europe, made it
possible to avoid the difficulty of ventilation connected with steam
traction in tunnels, and permitted the use of grades practically
prohibitive with the steam locomotive. The practicability of the tunnel
extension project finally adopted was thus assured.

The acquisition of the control of the Long Island Railroad by the
Pennsylvania Railroad Company, which occurred in 1900, introduced new
and important elements into the transportation problem, from a freight
as well as a passenger standpoint. Previously, the plans considered had
for their only object the establishment of a convenient terminus in New
York, to avoid the delays and difficulties involved in the necessity of
transporting passengers and freight across the North River. When the
Long Island Railroad became practically a part of the Pennsylvania
System, it was possible and desirable to extend the project so as to
provide, not only for a great prospective local traffic from all parts
of Long Island, but also for through passenger and freight traffic to
the New England States, and to and from all points on the Pennsylvania