A single swing gate requires the same amount of space as the width of the driveway (gate opening) regardless of which side it is swung from and how far it opens.  A double swing gate (hinged from both sides) requires only half this amount of space.

Hinges behind Post to take up less driveway Width 

Swing Gates can have the hinge inside the Gateway so the gate is in the middle of the post or it can be around the back of the post so the gate takes up none of the Gateway width or gate has a very wide opening angle.