yes, all teleports are one way. And if the waypoint happens to be buried underground, you spawn on the next highest surface immediately above it. So if you build a waypoint and a telepord pad on top and a second set.. you can pair them up and make a 2 way.
But that's not the limit. you can have ANY number of teleport pads keyed to a single waypoint. This is handy in creating a set of teleport transfer rooms, should anyone other than myself also want such travel tools.