Discussion related to commuter rail and rapid transit operations in the Chicago area including the South Shore Line, Metra Rail, and Chicago Transit Authority.

Moderators: JamesT4, metraRI

  by zmuzak
I was wondering how a train gets the right of way to cross an interlock. Is it the signal before the crossing, or the signal after. Or is it done by radio? Often at Deval or the interlock by Mayfiar, it seems the train comes to a halt after passing the last signal before the crossing.

  by c604.
The signal directly before an interlocking is the one that governs movement through it, the one after it would govern the section of track past the interlocking. They can be controlled by a person (such as Deval and Mayfair) or in some cases, I think Rochelle is like this: its on an automatic first come first serve basis. Permission given by radio is sometimes done if there is a problem and the operator can't get the signals to clear up to anything other than red.
  by doepack
Given the heavy amount of traffic at Deval and Mayfair, it isn't unusual for trains to come up on red home signals if the dispatcher has cross traffic lined already. Also, the process described in the previous post where trains are granted authority via radio to proceed past a signal displaying stop indication is known as "flagging". In these situations at manual interlockings, such as the two above controlled by UP's CY tower, the conversation will usually go something like this:

Tower operator: After stopping, train xyz has authority to pass signal displaying stop indication in an eastward (or westward) direction from track 1 to 1, (or 2 to 2, 3 to 3, or diverging combination, whatever the case) with no confilicting moves present...