Peter Nahodyl says:

The difference between code 80 and code 55 is the height of the rail. code 55 has a lower more realistic looking track some things to be aware of is on some rolling stock the wheel flanges may ride up and derail especially older stock however if you have items that meet NMRA standards you should not have any problems also as mentioned Atlas has Transition rail joiners that are needed

Wally Eastman says:

Code 80 rail is larger than Code 55 rail. You can combine them on the same layout as long as the flanges on the wheels that you run will not rub on the ties that the rail rests on. Remember the spike heads and tie plates.

Code 55 rail should be used on a branch line for HO scale.

Wally

Chris Manvell says:

From what Myk wrote, it looks as if it depends on what make of track you are using. If my memory serves me right, Peco 55 and 80 can be joined using normal fishplates. This is because the 55 rail is extended down into the sleepers making the visible height 55, but the actual height 80. Bit like —|-| cross section (rotate image 90 degrees cw). As it’s nearly 1.30 am I am not going to dig out some track now to prove it! You need to check that the flanges on the wheels don’t hit the chairs and that they pass through the pointwork smoothly. CM.

Sheldon Clark says:

Peco “N Gauge” Code 80 and Code 55 Track seem to use the same thickness of plastic for the ties/sleepers, and the same height of metal for the rails. The differences are that the rails of the Code 55 track are set deeper into the plastic than the code 80 track and that they are shaped to disguise this fact, with what looks like the bottom flanges set 0.025″ up from the actual bottom of the rails; the flanges thus appear flush with the tops of the bearing surfaces of the chairs on the ties/sleepers. As a result, a very short piece of Code 55 track connected by standard rail joiners to two pieces of Code 80 track will not be in contact with the underlying cork sheet or whatever the track is laid on, and will actually be suspended from its rail joiners. This should not make any difference if you ballast your track with sand, cork or grit and PVA glue, for instance. If, however you just lay the two kinds of track butting up to each other without joiners, there will be a distinct bump as your stock makes the sudden 0.025″ vertical transition from one to the other, possibly leading to derailments. Joining a longer length of Code 55 track to any piece of Code 80 will create a small gradient as the track transitions from being in contact with the cork base to being suspended by its rail joiners. There will be a less abrupt change of gradient (from up to level) where the two pieces of track meet, but this is less likely to cause problems except perhaps if you are using locomotives with several rigidly mounted axles, such as a 2-10-0. There may, however be visible flexing of the track under heavy stock as If you ballast your track with sand, cork or grit and PVA glue, this should not happen. Ideally, I suppose you should shim all your Code 55 track with 0.025″ (25 Thou.) plastic card, but most people will probably find this unnecessary.