. Electric railway journal . fectly satisfactoryfor movements at moderate speed and in locations wheresignals are not too frequent, but where signals have to be On the other hand, for slow-speed service the latestdevelopments in this type of block signals render it idealnot only because the first cost is exceedingly low butbecause no need exists for digging up the track, whenthe signals are installed, in order to rebond rails, insulatethe sectionalizing joints and remove tie rods as is re-quired with track circuits. The cost of a block I milein length may be said roughly to approximate $550, o
. Electric railway journal . fectly satisfactoryfor movements at moderate speed and in locations wheresignals are not too frequent, but where signals have to be On the other hand, for slow-speed service the latestdevelopments in this type of block signals render it idealnot only because the first cost is exceedingly low butbecause no need exists for digging up the track, whenthe signals are installed, in order to rebond rails, insulatethe sectionalizing joints and remove tie rods as is re-quired with track circuits. The cost of a block I milein length may be said roughly to approximate $550, ofwhich $400 covers the cost and erection of the twosignals and the two contactors. The remaining $150covers the cost and erection of, say, four line wires, afigure which would, of course, vary directly with thelength of the block in case any length other than 1 milewas used. SPECIAL FORMS OF INTERMITTENT CONTROL SIGNALSFour forms of intermittent control signals are in apractical stage of commercial development at the present. Light Signals with Two Indications, Pennsylvania Railroad Terminal in New York City passed at high speed and at short intervals the additionalduty imposed upon the motorman through the necessityfor ascertaining that each signal has operated, thus dis-tracting his attention from the track ahead, is generallyconsidered to be a drawback. In brief, it may be saidthat the track-circuit signal system is the only one now inexistence which is absolutely certain in operation andwhich in consequence does not need to have its operationchecked. This is accomplished, however, only at a com-paratively great expense, and if a less expensive form ofsignal is used, a greater degree of discipline for themotormen must be enforced to make up for it. With thisexception the most improved forms of trolley contact sys-tems leave nothing to be desired on the score of protection,nor do the latest forms of trolley contactor appear tolimit the speed at which they may be safely passed
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