You can. They are compatible but look different.

Atlas Code 83 is basically their old code 100 track with. .017” removed from the top. It has a much wider profile than the Peco code 83. ME code 83 is the same profile as peco just the ties are little different. You can use atlas joiners to join both the Atlas and Peco, you might need to squeeze the joiner tighter on the Peco side. I use ME joiners and I believe you would need to make them slightly wider to fit the atlas track. 

I wouldn't...

...At least not If I were a beginner.  Atlas and Peco code 83 have very different rail cross sections.  Since Atlas rail is thicker across the web and base, joiners that fit well on Atlas can be too loose on Peco, and joiners that like Peco can be overly tight on Atlas.  Getting nice smooth joints can be a chore if you aren't experienced in laying and tuning track.  

Once you have developed track laying skills, go ahead and start mixing brands all you want.  Until then you could be setting yourself up for frustration.  I've encountered a number of beginners who had a tough time working with Atlas and Peco together, especially when working the two in complex yard ladders and such.

Micro Engineering and Peco

I am using Atlas code 100

I am using Atlas code 100 flex track with Peco code 100 turnouts and prefer to use the Peco rail joiners as they are nice and tight on both.

Not a big deal...

I use both with Atlas joiners. Transitions are being made out as a bigger deal than they actually are. Appearance differences are dramatic though. I use Atlas flex for staging or less visible sections and Peco turnouts/flex for most everything. Inconsistency should probably be avoided for beginners though, but using both won't ruin reliability, poor tracklaying will.

Absoloutly

You can definitely blend, I've got a double crossover made up of a Peco medium radius right, Peco #6 left, (both code 100, everything else code 83) and two Atlas #6's for the other crossover. The yard ladder branching off of that, is an Atlas #6, Walthers 3-way, and a few Peco #5's. I've also got an Atlas #4 left and Snap Switch right mixed in with more #5's in the industrial area. 

Most of the trouble people have is the differences in tie height, and that can be remedied by styrene or wood shims, sanding down the cork, or some combination of both. You can also different codes by cutting the lips on a rail joiner with a Dremel wheel and then flattening one half of the rail joiner. The flattened part is soldered to the smaller rail and the other part is slid onto the thicker rail.

Anyways, sorry that was longwinded, but I hope it helped.

Yes , but

  It's probably a good idea to stick with one brand till you get some experience as long as you can get the turnouts in a configuration that fits your layout plan. If you need something from another manufacture to get the track alignment you want then don't be afraid to mix and match brands. With a little experimentation you'll find it's quite easy to make things work together. I'd suggest buying one piece of each brand of track and see for yourself the differences  in  cost/design/ construction method/ease of use,etc.......DaveB

Atlas Code 83 is basically

That is my biggest dissatisfaction with Atlas code 83. Technically it may be code 83 but with the wide profile when viewed from above, it doesn't look very fine.

That said, here is the trick, and why Rob suggested it's not a good idea for beginners.  This logical if you think about it - as long as the rail top and inside surface are flush with each other, flanged wheels will pass over smoothly.  So you can mix whatever you want as long as those two surfaces match up evenly.  You may also need to shim underneath the track as needed so it is supported when the rail is matched up properly.

As Rob pointed out, if you have some track laying skills, mixing track brands and even codes is not a big deal.  I mixed Atlas, Walthers code 83 and code 70 in my yard with no issues and in staging I mixed Peco, Atlas and Walthers, no issues.

I've decided to retire all of my Atlas code 100 turnouts for the next layout and have sold them all, and replacing them with Peco large code 100, but I will still use a few a one or two Shinohara turnouts where needed.

Below is an image Joe F

Below is an image Joe F posted to another thread. It shows various brands of track and the difference. There are several threads here that address the issue of mixing but it escapes me how to link to them.

Anyway, it goes back to the beginner thing but if you solder all your rail joints, and IMHO when you start building a permanent pike, you should, then mixing stuff isn't that big a deal. Solder is not normally known for mechanical strength but it does fine holding rail in alignment. A good pair of needle nose pliers, rosin core solder and a soldering iron can be used to tackle just about any sort of minor misalignment or rail height issue. One can even join different codes of track if they know what they're doing.

I agree with Rob Spangler

I agree with Rob Spangler, I would not mix track from different vendors if I could avoid it, especially if you're a beginner.

Based on the photo Michael posted just above, you can see the rail profiles are very different and you will get mis-alignment at the rail joints because of it.

Atlas wants their code 83 and code 100 products to be compatible, so their code 83 product has the same railhead as the code 100 product, the rail is just not as tall. While it works, it makes for a code 83 track that looks excessively bulky in up close photos and it won't easily mate with other brands without fiddling. See this photo of Atlas code 83 joined to MicroEngineering code 83:

 
Atlas code 83 rail (top) & MicroEngineering code 83 rail (bottom): railhead width is considerably different!

You need to align the joint properly on the inside railhead and then solder it to make sure it won't cause problems.

Better is to not mix track from different vendors unless you are willing to deal with the railhead width differences by soldering the rail joints.

You need to align the joint

Yes top and inside rail surfaces aligned and soldered and should be smooth rolling. 

I don't know if Atlas made the top of the code 83 wide on purpose to match the code 100, but that is a major visual  foul if the reason you buy code 83 is to give a more scale appearance and also make your trains appear more massive in relation, like the real thing.

The appearance does make a big difference and while I have used a lot of Atlas track in the past, I'm definitely leaning toward Peco code 83 going forward for it's much better profile.

"I don't know if Atlas made

   I think Atlas is a good compromise between appearance and ruggedness. Rail height in side view is the main thing I notice in person or photos so the rail being a bit more wide doesn't bother me much. Some things like couplers, flanges, and rail work better when not quite to scale so operators might be more inclined to go with more reliability while display/photographer modelers might go for more fine scale.....DaveB 

Quote:

Jim:

I have both smidge of Atlas 83 flex and a lot of Peco "Steamline" 83 flex. The Peco looks and handles the best, hands down.

As for switches, the Peco Streamlines are great. Love the built-in "Finger Flickin' Good" snap over point design.

Having sounded like I just gave a sales pitch for Peco, I will say also that I will be using three Atlas code 83 Custom-Line "wye" switches to create a very compact wye for an upcoming layout concept I'm designing.

However, I've done this model railroading thing for over 50 years with hundreds of feet of hand laying experience, so I don't foresee an issue in matching/smoothing up the joints.

Andre

Apparently code 100 is more

Apparently code 100 is more forgiving than code 83 as mixing the atlas flex with Peco turnouts has not been a problem and I have only had to address several miss alignment issues thus far.

Unavoidable

Just throwing my two cents in here, but if you are building a good size layout using commercial track, mixing manufacturers is going to be pretty much unavoidable unless you are willing to make compromises to your track plan to avoid it. (which, IMO you probably shouldn't do)

In my case I am using ME turnouts and flextrack for EVERYTHING... except where I needed a Walthers curved turnout for one section... and Watlhers bridge track over a couple of the bridges for appearances... and all that Atlas track in staging to save money...

Luckily, any issues with rail inconsistencies between manufactures can be greatly mitigated with a bit of solder and a small file.

The Peco looks and handles the best, hands down.

 Sure, when viewed from the side, true enough.  But we tend to view our trains more often from above because track height on most layouts is not at eye level.  Heck, it would have to be around 66 inches above the floor to view trains and track from side on.  I'd hazard that most layouts are closer to 50 inches, give or take, so the wideness of the Atlas code 83 rail is very apparent.  When the rail head width is closer to scale, it looks better and the model trains look more massive in relation. 

Andre,

I haven't handled the Peco code 83 flex yet.  How easy is it to bend and shape?  I have some Walthers/Shinohara code 70 flex and it is very stiff and requires a lot of massaging to get shaped and get the ties lined up and looking right.  The one thing I have liked about the Atlas code 83 is it is very easy to shape whether straight or a nice flowing curve.

I do feel Walther turnouts, with their use of stock rail for the points, looks more realistic than Peco, so Walthers has the edge in appearance, but being it is no longer made, and Peco has the built in spring, they are getting my business.

Thanks for the vote of confidence.  OTOH, I saved all of my track from my previous layout, but I have decided to make some changes for upgrades and improvements as my budget isn't as tight as it was last time around.  Toward that end I've already sold off all my Atlas code 100 turnouts and most of my Walthers and Shinohara DC style turnouts (code 100 and code 83).  That leaves me with all my Atlas code 83 and code 100 flex track still.

The old code 100 turnouts used in staging have been replaced with Peco large streamline turnouts and I've been slowly stockpiling Peco  code 83 turnouts for the visible part of the layout.  I still have all my Atlas code 83 turnouts - quite a few, which I may still used in some industrial area's if I end up needing them and don't have enough Peco.

The finger flickin good feature is nice as it there is no need to install any separate ground throws such as Caboose Industries ground throws etc.  I have some of them but find them a little awkward to throw - you have to get your finger underneath to pull them up and flip them around.  With the Peco, throwing is much easier and less awkward.

You mentioned using Atlas wye - Peco makes wye's too.  Why did you choose Atlas over Peco for the wye?  Or did Peco not make the right geometry wye for the application?  Walthers makes several different wye's as well.

I agree, especially since Walthers Shinohara line of track, with it's great variety, can really allow flexibility of track design and geometry. 

It's too bad that the old variety has been discontinued and the new Walthers track will be limited to a much smaller type so that flexibility will be harder to come by unless you can find old stock or get particular turnouts on Ebay.  

Originally I was using mostly Atlas track but I had to add Walthers for their specialty turnouts, such as the #8 curved which helped me cram more capacity into sidings or yards.  I also used #6 3-way and #6 double slip on my last layout.  So did have a mix of Atlas, Walthers, Shinohara and a few Peco on the last layout - no issues as I matched the rail up where connecting different brands or codes.

Since the new layout is planned to be DCC, I've sold off most of the Walthers DC type turnouts rather than have to do a lot of mods to them to make them DCC friendly.  I did manage to find on Ebay a couple of DCC friendly #8 curved for the new layout several months ago; they seem to be getting hard to find now and price going up accordingly.  I have some PECO curved as well.  I'll use what fits best for the application.

Walthers

Walthers is supposedly replicating their former Shinohara-made line of HO track and switches, with availability this summer.  We'll see what happens.  No idea who is making it for them.

New Walthers does not include most of the specialty turnouts.

Yes, but from what I saw, there were no curved turnouts, no 3-way or double slip etc.  So the specialty turnouts many of us turned to Walthers for do not appear to be on the foreseeable horizon.

Same vendor for track

Below is an image Joe F

Below is an image Joe F posted to another thread. It shows various brands of track and the difference. There are several threads here that address the issue of mixing but it escapes me how to link to them.

Anyway, it goes back to the beginner thing but if you solder all your rail joints, and IMHO when you start building a permanent pike, you should, then mixing stuff isn't that big a deal. Solder is not normally known for mechanical strength but it does fine holding rail in alignment. A good pair of needle nose pliers, rosin core solder and a soldering iron can be used to tackle just about any sort of minor misalignment or rail height issue. One can even join different codes of track if they know what they're doing.

 

 

I can't speak to the ME and Peco outside of this photo, but I think it may be a bit misleading for up-to-date Walthers and Atlas.

With a little careful work you can mix any kind of track (if it's the same nominal gauge, i.e., standard gauge, 3' narrow gauge, etc.) pretty much. You might need to solder the rail joint to get a good match, but it can be done.

 

Here I've joined Peco code 70 to Atlas code 100: