Summer Evening and the ML401

Summer Evening and the ML401
Conrail ML401 rolls west through Central New York farm country in Onondaga County, September 1994.

Friday, June 4, 2021

Correcting A Crossing Circuit - With Expert Help

As regular readers know, we have a fully automated grade crossing on the Onondaga Cutoff.  Just west of CP 277, Highbridge Road crosses the Chicago Line, and the grade crossing is protected by lights and gates mounted on posts.  These are automated through the use of sensors placed along the track - distant sensors, located so as to provide gates being down before a maximum-speed train's arrival, and 'island' sensors on each side of the crossing so that the gates rise immediately after a train passes.  

I used the Azatrax system for this as detailed in the March 8, 2019 post and have found it to be excellent.  

However, it was designed for a simple double track main line application - not one with a crossover between the distant sensors and the crossing.  Essentially, where the diagram above reads 'Track 1" there are switches that allow trains to cross over in each direction.  Therefore, depending on the sequence of traffic, the machine would be deceived by certain crossover moves, since the incorrect sensor would be triggered or missed, and that lead to unprototypical operations.  

After one of the Facebook Live video releases on the OC Facebook Page ( ) a viewer commented that he could help with this.  Matt Paquette, who is a professional signal maintainer for a major northeastern freight railroad, advised that we could use the internal contacts in the Tortoise Machine to re-wire the distant 'E' and 'W' detectors to provide proper detection for crossover moves.   Matt built a new diagram to follow.

Essentially, the Q1 output needed to be routed through the internal contacts in the Tortoise machines so that the grade crossing board would see the proper distant detection for the move.  It took some doing and soldering in tight clearances - not my best work - but it's functional, and seems to test out.  The true test will be an operating session!  

So, thanks to Matt, the Onondaga Cutoff just got more prototypical.   Matt's expertise helped where I had run out of choices, and this becomes another example of 'Let Experts Be Experts.'


  1. Replies
    1. One of those small electrical things that makes the crossing much more prototypical. Thanks!