I know what the OP is thinking, that you should not land on an occupied runway, but this hardly ever applies in the Gliding scenario.
Gliders run out of lift at times regulated by nature, and it could be that two or three gliders may need to land almost simultaneously. Fortunately most gliding fields are a big wide open space, so the first one lands, then the second lands to the right of him, and if there was a third, he would have to land long, over the top of the first two.
Then comes the problem that Gliders don't taxi, so they could be waiting for 10-15 minutes for the tow-crew to pull them back to the start location. If a fourth glider then needs to land, he then has to find a spot clear of the other three and the tow-crew, and the cables and winch.
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