I can't open the PDF, but I'll throw in my two cents...
First of all, CSXI downsized their network in 2004... the result has been fewer loads and more traffic going to truck and NS. They also "rationalized' unprofitable business, i.e., raised the rates so that the business would either provide profitability or go away. By focusing on a smaller core system, CSXI's revenue and profitability have improved dramatically on a much smaller volume level.
So it could be about reducing their network, or the fact that railroads are continuing their direction away from trailers and toward containers. Something like two-thirds of all intermodal traffic is by container now. The railroads fill their trains with equipment from truckload carriers (e.g., Schneider, Hunt), LTL carriers (UPS, Yellow), steamship cos (COSCO, Maersk), third-parties (CH Robinson), and even shippers. They'd just as soon not supply equipment if they didn't have to. The railroads lease much of their trailer and container fleets and often assign them to multi-railroad pools. All in the name of efficiency... the less equipment needed, the lower the company's operating costs.
PS - Railroads also formed a national boxcar pool as well to improve equipment utilitization (not related to Railbox, but managed by TTX). It's not a perfect system, but has been pretty successful thus far.
