ELECTRIC TRUNK-LINE OPERATION—_SPRAGUE. 147 
Derailments will crush one form of conductor to the ground, form- 
ing a short circuit which will cut off the section; but they may also 
knock down the supporting structures of the other, and, where there 
is a plurality of tracks, put them all out of service. 
In wrecking, the third rail offers some obstruction to the throwing 
of the equipment to one side; but, on the other hand, overhead con- 
ductors may interfere with the operation of the crane booms of the 
wrecking car. 
Where there are two or more tracks snow can not be piled up 
between them if the third rails are located there; but, on the other 
hand, overhead conductors are a source of danger to train men, to 
snowshed and tunnel repairers, and in the open are subject to troubles 
of sleet formation. . 
The third rail will oftentimes be covered with snow, but is un- 
affected by sleet. Very thor- 
ough tests made in connec- 
tion with the New York 
Central work show satisfac- 
tory operation, not only in 
sleet storms, but with the 
rail buried in snow. Addi- 
tional depth should not add 13%" Mh agyg! ——- 
much difficulty. With re- i 
gard to frogs and switches, 
there are no problems which 
can not be solved with this Fic. 3.—Details of Wilgus and Sprague pro- 
type of third rail, with an tected third rail on Philadelphia Rapid Transit 
occasional overhead section,  *"%*% 
and any required amount of power can be collected at operative 
speeds. 
On western roads, where a rotary snowplow is used, overhead 
conductors and the supporting insulators, especially in yards, will 
be subject to a heavy bombardment of snow, ice, and refuse, with 
possible resultant breakage, and the under sides of the umbrellas 
of the insulators will be often filled up with wet snow. 
Then there are corrosion and soot deposits when steam and electric 
operation are maintained over the same track. Where the steel sup- 
porting bridges also carry signals, as is proposed in some cases, 
there is increased danger to men engaged in cleaning, painting, or 
repairing overhead structures and taking care of signals;and when 
spanning two or more tracks there is a possible interception of the 
train operator’s view of signals because of dips in the railroad grades 
bringing overhead bridges in front of the semaphores, which like- 
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