on Wed Oct 14 10:51:31 2009, in response to Re: Here Ya Go...CTA New 5000 ACs (PHOTOS), posted by Steve B-8AVEXP on Wed Oct 14 08:00:16 2009.
I would guess that the historical cars , 4271/4272, still on the property and still used might have had a bearing on the series number. And the CTA has historically used a new number series to designate a fleet of cars incompatible with other cars. The 6000s brought in the PCC fleet. Don't know how the 1-50s fit into that. Then the 2000s brought in the air conditioned, high performance series which rolled over into the 3000s. So, maybe it was just that the 5000 number was next in line.