Good information all. But now, for something completely different, here's some food for thought................
In the track gauge department, I've got good news. And I've got bad news.
In the good news department, if you run your 1/48 scale trains on 1-1/4" gauge track, then your trains are to scale even though your track is not (5'-0" between the rails). Huh? 
And the bad news - if you run your 1/48 proto-scale trains on 1-3/16" gauge track, then while your track is to scale (or pretty darn close to the scale 4'-8 1/2" track gauge), while your trains are not. 
And more bad news for the 17/64" modelers, while your 1-1/4" gauge track is to scale, your trains are not. For the exact same reason as the proto-scalers running on 1-3/16" gauge track.
How's that, you ask? Because our models MUST have some sort of tolerance to be able to run on our miniature track (with our substandard curve radii). And 1/16" ~ 3/32" tolerance or so, seems to be a pretty good tolerance to shoot for in O-scale/O-gauge. Which translates into 3" ~ 4-1/2" full size tolerance measurement. And I guarantee, the full-size WHEEL FLANGE GAUGES on full size locomotives and train cars are nowhere near 3" to 4-1/2" LESS than the full size track gauges. Full size train wheel gauges (4'-7 1/2") are about one inch LESS than the full size track gauge (about .0208" less in 1/48 scale). And at .0208" less, our model trains would NEVER be able to successfully run on the sub-standard curves that most of us O-gaugers/O-scalers have to use with our models, due to physical space constraints. 
Doubtful? Measure the wheel flange gauges on any of your standard O-gauge or O-scale locos or rolling stock, and what do you get? About 1-5/32" to 1-3/16" across the wheel flanges. Which translates to about 4'-7 1/2" full size measurement. Which means your train wheels are gauged to scale! 
So there ya' go. In my opinion, all those modeling Proto 1/48 or 17/64" scale for all these years have probably been worshiping a false deity all this time. 
As for me, I enjoy the simpler things in life, like running O-gauge trains on 1-1/4" gauge track. Life's too short to fret over 1/16" or so, as far as I'm concerned. 
