Do 57 ft containers exist?

Interesting. The 57 foot number is repeated through the technical bulletin for their Maxi-Stack® IV car, so it's not a typo. So far I haven't found a reference to the actual existence of 57' containers; perhaps the capability to handle them has to be provided first.

53' containers are still a relatively newer development for international shipping.

http://en.wikipedia.org/wiki/Intermodal_container

The original domestic 53-foot box OTR containers were introduced in 1989, but in November 2007 the first 53 foot ocean containers were introduced. All new, reinforced 53-foot boxes are built specifically for international trade and designed to withstand ocean voyages. According to APL, 53-foot containers could become the transport method of choice for customers moving cargo.

The trucking industry seems to be pushing for longer trailers, so it sounds like GreenBrier is planning ahead. 

A quick google search of 57 foot trailers turned up this:

http://www.ltrc.lsu.edu/TRB_82/TRB2003-000701.pdf

There may even be 60 footers coming.

7 states permit over 53 feet. would be hard to move longer trailers states to state.

http://ops.fhwa.dot.gov/freigh...size_regs_final_rpt/

Wow, I saw plenty of guys having a hard time wheeling 40 footers around town in Chicago...can't wait for these.