Train movements on former JM&I lines were governed by PRR manual block system rules. The manual block system did not utilize automatic block signals (ABS). ABS was only in service in 1952 between IU Railway Interlocking in Indianapolis and Dale siding and between Clagg and Boyd.

On the Louisville Branch continuously attended block stations were located in 1952 at Dale (1.7 miles south of Indianapolis Union Station), Greenwood, Atterbury, Columbus, Seymour, Scottsburg, Boyd (the interlocking station at the north yard limits of Jeffersonville yard), and Clagg (the interlocking station at the south end of the Ohio River bridge in Kentucky). Three other block stations at Franklin, Crothersville, and Speed were open only week days during the day shift.

The manual block system also utilized unattended block limit stations, usually located at intermediate sidings between attended block stations. The block limit station allowed a second following or opposing train to enter the block between block stations. If the trains were opposing, they would meet at the intermediate siding. PRR Form “K” would be issued to authorize a train to proceed past a block limit station. Without a Form “K” the train was required to stop and telephone the controlling block station for authority to proceed. In 1952 there were block limit stations on the Louisville Branch at Garden and Brook sidings controlled by Columbus, at Elvin siding controlled by Atterbury, and on the Madison Secondary at Haw and Wren controlled by Columbus.

To learn more about the PRR manual block system and PRR lines at Louisville and Jeffersonville, and to view a schematic of the Indianapolis Division (which included the JM&I lines), see Notes on Pennsylvania Railroad Operation and Signaling at http://www.du.edu/~jcalvert/railway/prr/prrsig.htm