The reasons behind the transistion to left-handed operation after 2pm on Metra's RI district are twofold: First, the station platforms along track 2 between Blue Island and Joliet are shorter than those along track 1, meaning that track 1 can berth an entire nine-car train during rush hours. Secondly, and this may be more coincidental, is that for some reason, the parking lot development at all of the stations west of Blue Island are on the same side, i.e, along track 1, so I'm guessing Metra has some sort of "customer friendly" equation at work here. Ridership on this route has been growing steadily over the last few years, due in no small part to the explosive population growth in suburban Cook and Will counties, and although this route already sees 68 trains daily, that number is sure to increase in the coming years.
Form19, the old CNW did indeed run left-handed as a matter of standard practice, and UP carries on the tradition today, when it took ownership of the commuter lines from CNW in 1995. UP now runs the old CNW commuter lines under a purchase of service agreement with Metra.
Although CNW did take over Rock Island's commuter service in 1980 after the Rock went bankrupt, they maintained the Rock's operating style of "left-handed after 2pm" which had been established years earlier. But CNW only ran the operation for a year, at which time the RTA was formed, and subsequently took over RI's commuter service.
For additional clarity, I had posed my original question because this sort of "flip" operation was unique to me, not only is this the only Metra route that does this, I've yet to hear about this practice anywhere else. And since the LIRR has a rich and diverse history (learning more all the time, thanks in no small part to this board) it only seemed natural to ask the question here. Thanks for the edification, everyone...
--Dorian--