First Sub operations are a bit difficult to describe, but once you understand them, they run regular as clockwork. BICB departs Blue Island in the late hours of the night, and meets its counterpart from the previous day (CBBI) somewhere east of Rock Island. That CBBI departed Iowa City in the mid-evening hours the previous day. Exactly where the meet occurs depends on how early or late the trains are running. By sunrise, CBBI is well on its way into the Chicagoland area, and BICB is usually working the RI yard, or just arriving. Sometimes as early as 0700h and as late as 1100h, BICB completes its work and heads west into Iowa City, arriving in late morning or around noon, typically taking about 2-2.5 hours to traverse the distance.

Meanwhile, between CBBI's departure from Iowa City the previous day and BICB's departure from Rock Island back towards Iowa City, a turn runs from IC out to RI and back, known appropriately enough as ICRI/RIIC. This train essentially picks up cars destined for either customers west of Davenport or headed up to the interchange at Cedar Rapids. Sorting is done at Rock Island, since the IC yard is very poorly suited to train-building due to the numerous grade crossings surrounding it. The ICRI/RIIC are intended to shuttle these blocks of cars from the sort location (RI) back and forth from Iowa City. In addition, they also stop to switch customers, such as Cenpeco in Walcott and North Star Steel in Wilton, along the way. Any cars making it to Iowa City on a returning RIIC are typically then just forwarded onto the day's ICCR/CRIC trains, and likewise much of the CRIC freight is forwarded onto the night's ICCR. It's a relay race between these pairs of trains.

The Milan branch shoots out to the southwest of Rock Island. Where the mainline turns to cross the Government Bridge at the west end of the Rock Island yard, BNSF and IAIS share trackage out to the point where BNSF diverges to cross the Crescent Bridge (just south/west of the Centennial Bridge). From this divergence point, IAIS continues out to the end of track in Milan. There are a number of customers on this line, and it's serviced by the 5 day/week Rock Island Switcher (RISW). For more on the Milan Branch, see the Milan Branch page.