Though they cite no citations, Wikipedia appears to have a helpful section
here. Of particular note:
This appears to be supported by
Stars And Stripes and the German
Messerforum.
The 12 cm (about 4.7 inches) blade limit probably won't give you too much trouble when it comes to an EDC folder. The Messerforum posts seem to indicate that fixed blades with a 12 cm or shorter blade are acceptable. Since (AFAIK) all Emerson folders are locking and one-hand opening capable, they'd not be allowed. Most Spydercos (the Slipit line, which includes the UKPK, is a notable exception) are similarly disallowed. Basically, you'd want to go either the route of a non-locking blade (perhaps it's time to start carrying a SAK, Spyderco UKPK, or Sodbuster/Congress/Stockman/Trapper slipjoint), or a locking folder (like a Buck 110) that requires two hands to open. If you want to start carrying a smaller fixed blade, that'd be okay, too.