Are peco and atlas 55 compatible?

I've not tried it but I'd expect not.

The Peco code 55 uses a special "double T" profile rail and is actually more like code 83 total rail height, whereas I assume the Atlas code 55 track is a standard flat bottom rail with an inverted T shape.     To join the two you'd probably have to do something like grind away the bottom part of the Peco rail until you have a normal T shape profile, then see if rail joiners will fit the Peco and the Atlas rail?  Otherwise it'll be a case of a simple butt-joint with suitable packing under the track to achieve a matching rail height.

Any particular reason you want to mix the two brands ? I'd have thought the sleeper spacing of the Atlas track will be closer together than Peco and the difference will look a bit obvious?

Google found this old thread on another forum which seems to pretty much confirm what I wrote above, with another suggested option of soldering a short length of Atlas rail to the ends of the Peco rail before joining to further Atlas rail using rail joiners.

https://www.nscale.net/forums/showthread.php?37042-Atlas-and-Peco-Code-55

i read the thread title as "n gauge in us"

i guess it should be n gauge in US

Yep, everything Nick said.

mixing anywhere visible would be odd as they look markedly different, Atlas being US prototype, with longer, closer sleepers (/ties) and Peco being a bit of a generic UK/European mongrel! Atlas code 55 is fairly fragile, being proper code 55, and won't work with older models with coarse flanges, whilst Peco code 55 is designed for maximum compatibility.

Yes, as Nick says, file or grind off the bottom flange on the Peco code 55. I've used this method to joining Peco to ME rail without problem. Once the rail and sleepers are painted and the track ballasted the difference between the rail configurations is not particularly obvious.

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