IANAL (I Am Not A Lawyer) - but have had to analyze many cases to figure out what's going on procedurally and how/when it will apply to the organization I work for. This happens a lot in regulatory processes. As one court said about police: they aren't lawyers, but they have to know the law (and that includes how courts interpret it). Almost anything of consequence that a federal agency does (or, lately, does not do) with regulations is challenged in the DC Circuit or (for some financial things and patent/copyright stuff) Federal Circuit, and often gets appealed to the US Supreme Court. The Amtrak case is certainly "of consequence" for the railroads.

The Supreme Court "granted certiorari" meaning it has taken the case. It was appealed, probably by US DOT (because the Circuit Court decision found mostly in favor of AAR). So the Supreme Court will make some kind of decision. It may not be a detailed review - sometimes (often) they find some narrow reason to toss things, especially if they find that the previous court did something wrong. All that has happened so far is that they have decided to review it. The issue is over performance standards for railroads with regard to Amtrak, and how those standards are set.

See [www.supremecourt.gov] and scroll down to "13-1080
DEPT. OF TRANSP., ET AL. V. ASSN. OF AM. RAILROADS."

Since cert. was granted today, there's no further information. If you want to, you can check in at the supreme court web site from time to time and check on progress. The commentator linked by pdx has been strongly anti-Amtrak in the past, by the way.

The Circuit Court decision being challenged can be viewed at:
[www.cadc.uscourts.gov]

It's also linked in the Volokh article.