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Phil, There must be some more immediate ways to reach many of the same objectives without the burden of certified equipment. Why not change FAR 91.129 so that controllers are required to give explicit clearance to taxi on the runway? Also, airports can (easily?) deploy dynamic signs (e.g. traffic lights) which might be set automatically when a runway is active or manually to control arbitrary surface movements. Finally, in addition to the current system of named taxi routes, you might have color coding ("continue on blue, turn left on green") to make some information easier to convey. Aside from Tenerife, is there a correlation between RVR and the incidence of incursions? How many airports actually have ground radar? I understand that it, too, has problems in the rain.