I'm not very knowledgeable on technical things but something has been bothering me lately. I have been looking over a few pix and slides and noticed the pantographs on both the 1700s and 4000s.
In the beginning(the LRV era) the 1700s seemed to have pantographs
in the front with trolley poles still on the back for not so obvious
reasons(we'll get to that later).
  I noticed that in the later years to last days of PCC cars, the
4000s seemed to have 2 pantographs attached, one on the front, and one on the rear. Was there a reason for 2 pantographs?
  Also noticed a few cars(both 1700s and 4000s) with pantograph only
on the rear. Did PAT keep the pantographs on the front of the 1700s
until they were decommissioned?. When did they add them to the rear?
  Now getting back to my earlier statement.  I have a few photos and
slides from 1982-84. Why did they use trolley poles when pantographs
were installed? I have seen one particular photo that puzzles me.
4003 and a car following(either a 1700 or 4000 series car in final
white paint scheme-can't read the number) at the Bon Air stop on the
old Overbrook line. Second car is chartered(anyone on this trip?).
First car is signed 47L West Library via Overbrook and has 2 pantographs. Second chartered car only has one pantograph on the rear.
Don't know the exact year but has to be 1993 or earlier. Why did
some cars only have one pantograph while others had 2? And why 
weren't the pantographs used in the 1982 era and not the poles?
I used to think that poles were used on the Overbrook cars but this
photo shoots that theory down. This is all very confusing to me.
  If anyone can clear this up, I'd appreciate it.