No 6’ gauge in 1912, afaik ;)  

I think that the center track is demonstrating a style of guard rail.  I can’t tell if the guard rails are the inner or outer rails, but there are photos of up to 5 rails on a PRR line at a similar time.  One theory is that the extra rails may have provided additional support for blind locomotive drivers on tighter curves, but that theory has the logical problem that the support is only on one side of the rail, yet the track curves in both directions.