There is usually an Amtrack train that runs to Houston and beyond every other day.  You could check to see if they are running.  I know they are also using trains in the evacuation, however. 

Also, if you can reach your nephew tell him to call in to a local Baton Rouge radio or television station.  There are several Baton Rouge stations broadcasting 24 hour call-in formats.  They take callers with a question or problem such as yours.  Many local citizens will call back and offer to assist.  Church groups also are helping individuals that have a place to go, get there. 

Go to www.wbrz.com for local Baton Rouge area information.  You may be able to call in directly to the station and be referred to a local organization that will have someone to drive your nephew to Houston.  If I were closer to Baton Rouge, I would offer to go myself but I really have my hands full.

Let me know if any of this helped.   If not, I will see what else I can do.

Debbie Thibodeaux