Chicago, Milwaukee, St Paul & Pacific Railroad

by John Hinson

Savanna tower
Photograph 4/60, by Dr. J W F Scrimgeour

At Savanna, the double tracks of the Chicago, Burlington & Quincy crossed those of the Chicago, Milwaukee, St Paul & Pacific. This view of the crossing was taken looking along the Burlington company's Chicago to Twin Cities line, with the Milwaukee concern's Chicago to Omaha line crossing in front of the tower.

Interior of Savanna tower
Photograph 4/60, by Dr. J W F Scrimgeour

A GRS table machine was provided at one end of the tower controlling a flat crossing remote from the tower of the Savanna - Davenport line across the Burlington's line towards Chicago. The plan or signal board above shows the layout of this remote part (the tower and its crossing are shown at the far left) and it is remarkable to consider that the layout shown could be controlled from a six-handle machine. The signal handles do, of course, operate like push-pull levers so more than functions in two directions are possible. According the the plan, the manipulation is as follows:

1 Along main line towards Chicago
2 Along main line from Chicago
3 Along siding parallel with main lines
4 Along lower of two curved sidings on plan
5 Along upper of two curved sidings on plan
6 Across flat crossing

The actual connections between the sidings and the main line were worked from the mechanical frame in the tower.

Beneath the board are three clockwork time release devices, which ensure a delay should a route have to be cancelled. This type of time release was also used at a few locations in the UK - see Harrow No2.

Table machines were so-called because they were designed as individual free-standing units that could be built up to a required size, rather than a pre-manufactured interlocking machine which would stand on the floor. Table machines could be placed on a shelf or table, although these would have to be quite strong to take the weight!

About the photographs

Comments about this article should be addressed to John Hinson