3340/3341

I think this was the pair I saw in a train during the weekend. Both cars had yellow expanded metal decking on the roof. Anybody in the know have an idea why the stuff is there?

I think your numbers are off - probably thinking of some cars in the 34XX series - but you weren't imagining things, some cars have yellow roof boards. They're on a small sub-set of 3200-series cars formerly equipped with pantographs, for when the Yellow Line ("Skokie Swift") required them: http://www.youtube.com/watch?v=ghy-WjRqGzo

Didn't some of the cars with roof platforms never even have pantographs put on them?

I think all cars with roof boards were originally equipped with pans, but some of them had the pans removed within a year or two of them being delivered, and those cars were then assigned to the brown line. I guess they initially over-estimated the number of cars needed for Skokie service. Also around that time Saturday service was cut from the Yellow line, which might have something to do with it.

There are also a few pairs of cars out there which have the footings for roof boards, but no actual roof boards. I can't figure out if these initially had boards but they were removed, or they were built so that they could be skokie-equipped later on.

I wonder what happened to all the pantographs.

There's a pile of them sitting in a storage area at IRM.