Don't expect trailer-on-flatcar to go away anytime soon, but expect it to increasingly be via 53-foot trailers.

In FTR's "State of Freight" webinar Thursday, senior consultant Larry Gross noted that 48-footers, once the backbone of the intermodal system, are disappearing, down 20% year over year. 53-foot volume, however, is still running a double-digit improvement year over year.

"53-foot trailers are a major conduit by which new trucklines get into using rail intermodal. They don't have the containers; they like to put their trailers on the flatcar."

And while a few innovative programs have started putting temperature-controlled containers on the rails, Gross said reefer trailers on flatcars are still the far more common choice for perishable intermodal loads.

For intermodal overall, Gross predicts we'll end up at 4.8% growth for 2011, will see roughly the same in 2012 at 4.9%, then increase in 2013 to 5.6% growth. Domestic moves are growing at a higher rate, around 7%, than international containers, which are pulling down overall intermodal growth with 2.7% growth forecast for this year and next.