Well, THEORETICALLY speaking, gliders are only flying under VFR rules, in class D to G areas.
In class D, the transponder is mandatory and the traffic information and separation is managed by ATC.
In all thoses class (D to G) airspaces, the see and avoid rule is in force. A glider pilot allways fly with the "nose outside". He never needs to look at his instruments. Exepted some seconds each 10 minutes on the GPS.
As the glider is unable to keep strictly his altitude, when he's transmitting his position, he'll give an average altitude or a range such as "flying from 3000ft to 3300ft".
The two only problems are :
- The IFR flight descending into non controlled area to save time and not using the see and avoid rule
- The military jets who flies at very high speed and below 1500ft, unable to see and avoid. We have a circular in France advising all civilian pilots that they must avoid to fly from ground to 1500ft as the military aircrafts are able to practice tactical flight training at any time and any location.