Is there a distinguishable difference?

Traditional is just a fancy word for Non-Scale and Standard O is what Lionel uses to describe their full scale sized equipment.  Most scale equipment is going to be bigger than traditional O gauge items because it's not restricted to having to run on small radius curves.  That being said, there were smaller prototypes in some cases, which means the model might be on the small size.

You can tell the difference between traditional and scale sized equipment of the same or similar prototypes at a glance. You did not specify which Lionel Cab Forward you are getting; there is a scale version and a Lionmaster version. Both have TMCC and both are modeled after the AC-12, but the Lionmaster is about 10-15% smaller than scale. A Lionmaster Cab Forward is big enough that it will look OK with either traditional or scale size freight cars, but if you put an old Lionel 6464 boxcar next to a scale 40' boxcar, they will not look right together. Traditional size freight cars will look like American Flyer S gauge cars next to a scale Cab Forward, Big Boy, etc. I have a Lionmaster Big Boy and a number of different scale articulated engines, including a Cab Forward, and I prefer to run each with its own size rolling stock. 

Here is a comparison photo I made of three Lionel boxcars. The one on the left is traditional size, the same as the old 6464 series. The middle one is a Standard 0 (scale size) model of the same prototype car, a steel 40' boxcar of the late 1930's. The car on the right is a Standard 0 model of a newer and larger 40' boxcar, the PS-1 car from the 1950's. You can see the variations in size between traditional and scale, and also between prototypes of the same length boxcar. Click on the photo for a larger version. 

Great comparison shot! Thanks.

It really puts it in perspective.

Peter

Not to be obtuse, but there are typically dimensions, in inches, for locomotives

in the catalogues and on the company websites...so it shouldn't be hard to determine

if there is or isn't a gross disparity in size between two items... 

Your Polar Express is a truly a toy, and the Lionel Alton Limited is a 1:48 scale model

(actually, the Alton 4-6-2 is bigger - longer - even than it should be; I've got the set - love it regardless).

Remember, however, in the prototypical world, there are also great disparities in sizes - different lengths and heights in virtually every type of car, and much variation in engines as well. 

Not sure what you mean by asking if the AC-12 will be "size worthy," but it will be "scale" in size, and a fairly large engine.

I have a scale Cab Forward....I also have a Polar Ex 2-8-4 loco. The PE loco looks silly on the layout at the same time as the Cab Forward. I have Scale days and Traditional Days. Like them all!

Yes, but. Last Christmas (on our club modular layout) I was running my 3rd Rail Brass Scale Pennsy 6-8-6 turbine pulling six 21" passenger cars. A kindly grandfather was holding his grandson watching my train run. He said:

" See! This here is a LIONEL! Santa brought me this exact same train set to me back in 1950! Someone has painted the wrong number on this one though. Mine took smoke pills and smoked a lot more than these choo-choos."  

A child's memory in a 70 year old mind can be touching... His 1950 postwar Lionel Turbine was Scale.

Gilly

Well, that's about the most extreme example of a difference!   On the other hand, the more traditional-sized Lionmaster NYC Hudson is 22" long, and the scale Legacy NYC Hudson is 24 3/4" long. In this case, not an inordinate difference in length. There's all kinds of variations out there, of course.

Talking about more than that.  As I said, there's are all kinds of variations out there. Even within the traditional and semi-scale types, there are different sizes. For example the Postwar size "traditional" Berkshire is larger than a "traditional" so-called Baby Berkshire in the Lionel line. Lionel has made at least half a dozen different Hudson sizes, and then there are all the different sizes other manufactures such as MTH have made.

Seems like there's 1/48, and everything else is all over the place.

In the photo below, all of the boxcars are O-gauge. I'm not sure if any of them are O-scale!  lol

That's part of the fun and mystique of O!

Most people see three rails and "know" it's O scale Lionel toy trains. Even the stuff actually made by other manufacturers too!  LOL

There is no exact "scale" for traditional sized stuff.  Most is under 1/4" scale, some is over 1/4" scale.   Indeed, the scale can even vary within the same model in relation to height, width or length.

Lionel was and is still a master at this.  They manage to shrink or expand most items and it still looks "right."  Lionmaster locomotives were the finest examples of this.

Rusty

Is the AC-12 you're considering Lionmaster, Railking, Premier or full-sized Lionel?

Taht info would be helpful in this discussion. Not sure if MTH orLionel made this model in both sizes.

Thanks SWH for posting this image and description regarding sizing of boxcars etc. I had wondered why some boxcars seem somewhat small while others appear larger.

I prefer the middle size (Standard O as you ID'ed it). To be honest, I am actually disappointed at the smaller "traditional" size boxcars in my collection. I still run them on occasion, but I always wish they were "standard O" size.

I am curious about the Lionmaster TMCC Cab Forward. Where does it fall in the scale list based on the boxcar comparison in the photo?

Although it is 10-15% smaller than scale, a Lionmaster Cab Forward is still a large and impressive locomotive. It will look good with either scale or traditional size rolling stock. It is probably best suited to run with Rail King semi-scale cars, most of which are bigger than old Lionel but smaller than scale, but it will be fine with whatever you choose to run with it. 

I have a Lionmaster Big Boy of similar size. I prefer to run it with traditional or Rail King cars, but that is strictly a matter of taste. I have scale size steamers to pull my scale size cars, so that's how I operate, but I could just as well use the Lionmaster engine if I wanted to. 

Sort of in-between. Lionmaster engines are bigger than "traditional" size, but still about 10% under scale. By the way, the car on the right is the same scale as the one in the middle, just a taller prototype. 

Thanks for the info SWH. In the future when I run the traditional size boxcars I will keep all of them in the same consist and not mix them up with the larger rolling stock. 

Related question: has Lionel ditched the Lionmaster series? Will there be no more?

Don't forget, though, that in the real prototype world, there are all kinds and sizes of rolling stock in use - big, small, short and tall. For the most part, there's no such thing as a size-matched train.

Put another way, what Lionel said was that there was very little cost difference in building a scale-sized engine as opposed to a LionMaster one, so it wasn't possible to build LionMaster engines and market them at a price point significantly lower than scale engine prices.

That is indeed too bad. The fact that scale engines can be made for only a little more cost doesn't help all the folks - no doubt the majority - who don't have huge layouts that can support the full scale stuff. For many of us, LionMaster would still be an attractive option even at the price required. After all, there is no other Legacy semi-scale game in town.

Thanks Gents, I picked up the Lionmaster AC-12 plus a Legacy L2A Pilot Mohawk, the AC-12 fits in perfectly with the other Steam Locos that I have.  I had to pick up the LionMaster because although my layout (which is still on Paper) has O-36 to O-72 track on it, the layout doesn't support a continuous O-60 or O-72 track that I can utilize without other size curve track getting involved.  The AC-12 can run on small radius curves and still measures up in size closely to the larger steam locomotives.  I am going to include an O-72 loop around the layout and hope it pans out when the actual layout is set upon the table.  Once again, thanks all of you for your support, your knowledgeable input has been invaluable..          MARSHELANGELO