I just saw a dvdtalk review of Traffic Criterion with a release date of 3/7/06. So I went to some online stores to check it out. They also list it with the same release date but it has a different UPC than the old Criterion one. Does anyone know what's difference between the two releases?

Nothing different, other than the UPC. They're just re-releasing it so that it gets greater distribution. So if you've already got it, no reason to double-dip unless you're an insane completist who must have every release, no matter how minute the change.

I saw a couple copies of the original release, back in December. So, it must still be available. I picked a copy up for around $36 CDN.

So no new features, transfer, etc.?

None.
I was hoping for a cheaper MSRP with the wider distribution but oh well.