How to control current with a bridge operation!

You asked how I would do it.  I am not the most knowledgeable, but I would just add a micro switch and use a relay to cut power to a block before and after the bridge.  Depending on how fast you run, you probably only need a 3 or 4 section block.

I'm not sure how LEGACY and TMCC locos would like that.  The sounds and everything would go away.

Another option that would work well on a conventional layout would be to use the relay to switch in either diodes or resistors or a secondary transformer at down around 2 volts.  Train would come to nearly a stop but the sounds, headlight, etc would stay on.

Another thing that would be neat would be to add a solenoid lock to the bridge.  Set up a sensor track or trigger track to lock the bridge closed when a train is within 4 tracks.

I use two micro switches (one on each end of the bridge) to close the circuit to dead sections of rail extending severl feet back from the span.  Thea serves well to keep distracted operators from running into the void or upright bridge.  What that doesn't address is someone backing a train longer than the dead section into trouble.  Last year I posted photos and text showing how I built and wired my lift (it swings up) section.     If you search through my posts you'll find it.

I use a relay and insulated sections on either side of my dropdown bridge, which also works on my Atlas Bridge.  Here is a diagram:

Basically, I took the sections above (center one is the bridge) and isolated the them.  Then I got a relay with a dedicated transformer and put an interrupt inline with the power (the latches for the bridge section).  On my Atlas bridge, I used RC plugs.  For your application, a mini switch that disengages when the bridge is up would work.  Then I took my track power to the input side of the relay, and ran wires from the output side.  When the latches are closed, I have power from C1 to A1 and C2 to A2.  When they are disengaged, then the relay trips and power is cut to the tracks.

This may fall under the TMI category, but here's the wiring for the lift bridge for the North Penn O'Gaugers modular club.  There are two microswitches to sense the bridge closed, a DC coil relay, and it controls power for two tracks.  It's wired to power down the adjacent module to give some stopping distance.

I have not seen this in the model RR world but many real RR bridges incorporate powered de-rails near the bridge approaches, to put an uncontrolled engine or car "on the ground" as opposed to "in the water".  If anyone has done this in O scale, please share!

The GN Man posted:

I have not seen this in the model RR world but many real RR bridges incorporate powered de-rails near the bridge approaches, to put an uncontrolled engine or car "on the ground" as opposed to "in the water".  If anyone has done this in O scale, please share!

One of our engineman didn't get quite stopped before  a open swing bridge. He went over the  derail but not in the drink.   I suppose it wasn't funny but he tried to back up with the engines on the ground. When unsuccessful he  walked to the highway and hitch  hiked home only to heard of a  week  or so later.

As a result he was given professional help and later became     a permanent  fireman.   

How about the bridge getting the feeders wire  right at the hinged end on the bridge (underneath) ,  the bridge now  distributes the power to each block on either side via Plugs .    I guess it depends on whether  you want to bridge to be operational or is it  just set in place  while operating the layout.

This one has about 30 feet of insulated track on both tracks  controlling the bridge at one end. Not so much at the other .

Anyway here's a pic.   Yep, that's a 6 foot bridge at the very far end in the other pic. It's high enough so no ducking under.