Doors and trap doors are supposed to be equivalent, the crafting recipe is just turned by 90°, they work the same way, there are wood and iron variants (and different wood sorts for doors, but maybe that will come one day for trapdoors, too). BUT: If you craft doors, you get 3, if you craft trap doors, you will get 2. This is an inconsistency and also not realistic, because trap doors are half the size of doors, so they should, if different, it should be double the amount you get of doors.
But I would suggest changing the number of doors you get to 2, not the one of trap doors to 3 or 6, because having three doors is useless in most cases. Or change doors two 2 and trap doors to 4, that would be most useful and also realistic.