If you don't already know: The spike traps and barbed wire are supposed to be dug into the ground so their top is level with the ground.
If you just place them on level ground they will be seen as a block that is in the way, so the zombies will see a faster path circling around them. Put them into the ground and the zombies will happily walk over them and as a bonus even avoid those holes where a trap has been destroyed since a hole would slow them down as well.