Subdivision 4B, also known as the Audubon Branch, was the other long branch originally connected with the IAIS system. Breaking off the mainline at Atlantic, IA, it went 25 miles north to Audubon, IA, and was abandoned in 1995 for lack of traffic. Originally this was to be the home of the Purple Martin steam-powered tourist train, which was based at Lorah (the station near the I-80 / US-71 interchange), but the owner of the equipment suffered a fatal heart attack in the late 1980s. Plans for the train fell apart from there, and the equipment sat in a small yard visible from the freeway for many years afterwards. The crown of the collection was CB&Q Hudson 3007, which is now safely stored at the Illinois Railroad Museum. As of September 1995, the equipment had all been sold, and shortly after moving it all out, the branch was abandoned and scrapped.

The third small branch on this segment - a tiny piece (4.5 miles) between Hancock Jct. and Oakland, IA - continues to this day, though I don't believe there are any revenue customers left on it. The line was originally built by the Avoca, Macedonia and South Western Railroad in 1879, and was absorbed by the Rock Island only a year later in late 1880. Originally stretching down to near Sidney, IA, and north to the original Rock mainline at Avoca, IA, the line was cut up into segments over the years. The line was cut south of Hancock in the 1950s, and everything north of Hancock was scrapped in the 1970s. The branch is in relatively bad shape, and every time I've visited it, it's been populated with cars in storage.

A fourth, often forgotten, branch exists on the Fourth Sub, known as the Grimes Line. This 11-mile branch, breaking from the IAIS mainline in downtown Des Moines, travels northwest through Clive to the outlying suburb of Grimes, IA. It's actually owned by the Norfolk Southern (yes, the NS reached Des Moines, via the old Wabash at one point), but IAIS is the contracted operator, since it's isolated from the rest of the NS system by a long stretch of BNSF trackage rights. The original Wabash main is long since abandoned. Originally the line went through, but since the 1970s has ended at Grimes. The Des Moines switcher is responsible for servicing customers along this route, with the primary customers being Pitt Des Moines (a steel fabricator) in Clive and Beisser Lumber in Grimes.

Today's Fourth Subdivision operations largely occur at night. CBBI leaves Council Bluffs eastbound in the late evening. Its counterpart, the BICB from the previous day, rolls westbound over the sub in the wee morning hours, arriving at Council Bluffs in the early morning hours (0600h - 0800h). The Council Bluffs switcher, however, is out in the Council Bluffs yard during the day, and often runs up as far as Hancock to collect or deliver grain hoppers to the elevators. Also the yard is the site of IAIS's heavy locomotive maintenance facility, which is easily seen and photographed from South Avenue. Also, the Des Moines switcher is out during the day, servicing the Grimes branch, the Prairie City line, and local industries around Des Moines. Also, in addition to the IAIS traffic, Union Pacific detours across the Fourth are not uncommon, arriving at Council Bluffs and departing the IAIS at Shortline Junction in Des Moines, or vice versa.