. Electric railway journal . t is The circuit which is completed when a car standsover one of the third-rail sections, in addition to itscontrol of the lights in the cab, is utilized for telephoniccommunication direct from the cab to the dispatcher, anda motorman can receive his orders without leaving thecar. This system is more costly, although it is much lesscomplex in the details of apparatus than the ordinarydispatchers telephone systems. It is, however, less costlythan track-circuit signals designed to give the same trainspacing when absolute blocking is carried out for follow-ing movemen
. Electric railway journal . t is The circuit which is completed when a car standsover one of the third-rail sections, in addition to itscontrol of the lights in the cab, is utilized for telephoniccommunication direct from the cab to the dispatcher, anda motorman can receive his orders without leaving thecar. This system is more costly, although it is much lesscomplex in the details of apparatus than the ordinarydispatchers telephone systems. It is, however, less costlythan track-circuit signals designed to give the same trainspacing when absolute blocking is carried out for follow-ing movements, and of course when permissive followingmovements are allowed the spacing of trains in the samedirection may be very much reduced. The cost of in-stallation for a 50-mile line with sidings 5 miles apartapproximates $800 per mile. INTERMITTENT CONTROL SIGNALS Special interest attaches to the group of signal systemswhich may be classified as the intermittent control types,among which only the trolley contact signals are now. Light Signals Near Berkeley, Cal., impossible to set the pair of adjoining handles so that theleft-handed one points to the right and vice versa. Ifone handle is moved to the right, say, and thus gives aclear indication to the train at the corresponding siding,the next handle to the right must be kept vertical, holdingany train which may be at the adjoining siding. In thisway trains at adjoining sidings cannot both receive clearsignals to approach each other and thus meet head-onbetween sidings. In addition, the handles in the latestform of this signal are electrically interlocked so thatwhen once a train is in a block it becomes impossible tochange the position of the control handle and thus opena way to let an opposing train into the other end of theblock. Opposing movements of trains at a meeting pointare controlled by the two outer third-rail sections of thegroup at the siding, and two trains which approach thesame siding receive danger signals as soon
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