Choclit runway has it. And at Heathrow about 30% of traffic is heavy, creating a large number of vortex gaps.
One other characteristic of mixed-mode is its resiliance to strong headwind. As the headwind increases the time interval between traffic spaced 3nm apart increases and therefore fewer aircraft per hour cross the landing threshold. As 3nm is the minimum radar separation there is noting one can legally do about it.
However, in mixed mode the longitudinal separation on final approach is well above radar minimum and so provided there is no vortex element required, the physical spacing can be legally and safely reduced with increasing wind in order to preserve an acceptable time interval (time based spacing). A mixed-mode runway does not therefore suffer in strong headwind as a segregated runway does.
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