It's my understanding that AASHTO's current plan is to not issue any more editions of LFD (although interims are to continue until 2007 - I think). Therefore, it seems that most states will soon have to adopt LRFD or maintain their own LFD standard.
Qshake is right. The concepts are similar. BUT, The AASHTO LRFD Guidelines are VASTLY different than LFD. I would suggest to all who are planning to continue in bridge design to invest in the latest LRFD manual. It's not an easy leap; it will require alot of reading beyond the "articles". Fortunately, the LFRD is written similar to the ACI in that there is a running commentary on the same page as the article (I found this very helpful).
The LFD code was written similar to ACI's (1.4DL + 1.7LL, etc.). The LRFD codes have incorporated specific bridge studies to incorporate bridge statistics (not buildings) with alot of consideration to areas not specifically addressed by the LFD (e.g. skewed bridges).
TxDot = LFD/ASD - but looks like maybe a very (could be really slow) move to LRFD.
On a side note - I am working at getting my masters degree in structural engineering at night at the University of Houston. I took a bridge design course last spring and we were taught the LRFD code. I do believe that TxDot is beginning to look at what it might take to switch, but I could be wrong. TxDot has issued some standard bridge designs (for just a CIP slab bridge) using the LRFD code.