I just made an interesting discovery in 34.08. Not sure if it's a bug or intentional. Cage traps seem to block wagon access now. I had a trade depot built like this:
top view
==XXXXXXX = Stockpile (inside fort)
==XXXXXXX X Soil wall
==XO OX . Floor
==. X O Depot
==. O X ^ Cage trap
==X X ╔═╗ Bridge
==XO OX ╚═╝
==XX^^^XX
==XX^^^XX
XXXX╔═╗XX
XXXX╚═╝XX
XXX......
.........
XXX......
When I hit 'D' to check depot access, it would show the depot as inaccessible, with no green squares at all. Usually you get green tiles leading to whatever is blocking access, but I was getting nothing at all but the center of the Depot showing up as yellow on green 'D' meaning "Inaccessible Depot".
XXXXXXX
XXXXXXX
XXDDDXX
XXDDDXX
XXDDDXX
XXXXXXX
XXXXXXX
So I removed the top 3 cage traps, and now I had one more yellow on green 'D', where the cage traps were.
XXXXXXX
XXXXXXX
XXDDDXX
XXDDDXX
XXDDDXX
XXXDXXX
XXXXXXX
So it appears that cage traps block wagon access to depots now.
I'm going to try out some weapon traps and see if they also block access.
Not being able to put traps on the path to our depots will cause a lot of changes to the way many of us build forts. I don't know if this is a bug, or if Toady did this intentionally to add more challenge. It will certainly do that, whether it's a bug or not.
I'm running 0.34.08 on linux, if it matters.
Edit: I removed the second row of cage traps and now have an accessible depot.
Second edit: I added a weapon trap with a single silver battle axe, and it blocks access. So weapon traps also block it. Shit just got real.
Third edit: Pressure plates and stone fall traps also block access. I can't try upright spear/spike traps right now, since I don't have any spears or spikes. But I'd be willing to bet they block access, too.