[Aloys]

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For instance: What sanctioning body disallowed the Nurembergring (in the late 60's?) for competetion with the FASTEST cars until track improvements were made? Guard rails, smoothing out the "bumps", cutting away the brush and some trees and generally making the "old" track not just safer but even faster!

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Excaliber, you mentioned the Nuerburging:
1968 Jackie Steward winner on Matra-Ford
1969 Jacky Ickx winner on Brabham
1970, after several accidents during training-session, the speaker of the F1-Driver-Association, Jochen Rindt, declared the track as to dangerous, no race took place. Then the "improvements" you mentioned were made.
1971 Jackie Steward winner on Tyrell-Ford
Finally, 1976 the winner was James Hunt on McLaren Ford. At this race, Niki Lauda had his accident and the Ring went to sleep until 1984 when the new short Ring was opened with a Race of F1-Drivers, all in similar Mercedes-Cars. I witnessed the victory of an until then unknown driver named Ayrton Senna!
The GP that year was won by Alain Prost and McLaren.