I like the idea of traps being indiscriminate. Think of all the traps in the indiana jones movies. The spear traps in 1 or the serrated blade traps in 3. If there was a way to link traps with a lever to turn them on or off to let people past them, that would be great.
It would be especially nice if it was possible to assign a few guards to man doors and trap activation/deactivation levers so the process would be automatic. Front gate guard stops the caravan at the entrance since corridor is marked dangerous (or rather, all the squares are marked dangerous as traps and the FRIENDLY caravan waits next to the guard who warned them) inner trap operator guard pulls lever, traps are deactivated and the squares are now safe to cross, caravan proceeds through and the guard reactivates the traps automatically.
The process would be repeated with dwarves wanting to go outside.
Insufficient number of guards would result in traffic jams as dwarves waiting for the traps to be deactivated by the player or FRIENDLY units wandering into trap fields since they weren't stopped by guard.
As a side note. If you use a checkerboard pattern of traps and mark the trap squares as restricted traffic squares, dwarves will avoid stepping on the traps while goblins/animals will take the shortest past through. "Step only on the black tiles, the white ones are trapped."