| Sporting the "Automatic Train Control" sign is this 1944 Baldwin 4-8-4 Northern built as RFP #619. Much like a very early Positive Train Control system of today, Automatic Train Control was a system designed in 1922 by Union Switch & Signal for the PRR who called it Pulse Code Cab Signal. Itvworked by sending metered pulses along an existing AC track circuit operating at a chosen carrier frequency. The pulses were detected via induction by a sensor hanging a few inches above the rail before the leading set of wheels. The codes would be transmitted to the train from the block limit in front of it. This way if the rail was broken or another train entered the block, any codes would not reach the approaching train and the cab signal would again display "Restricting". No date or photographer was listed for this photo. |
| Date:
6/1/1950 |
Location:
Alexandria, VA |
Views:
213 |
Collection Of:
 
Gary Everhart |
| Locomotives: |
Author: Gary Everhart
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| Picture Categories: Roster,Yard,Steam |
This picture is part of album: RFP "Pulse Code Cab Signal" |