#5 No more racing to the line.
It may have not been a popular first decision, but shortly after assuming The CEO role in 2003, Brian France quickly implemented a rule that disallowed drivers to race to the line when the caution flag came out. The move was a huge departure from the race to the line finishes that fans have enjoyed in the past, but it was a huge slide in the right direction from a safety standpoint.
Not only did the new rule allow for safety crews to get to drivers quicker after an accident on the track, it also prevented drivers from being overly aggressive to try to nab the win at the line, which could have produced even more safety issues. Of course NASCAR fans hated the rule and fought it every step of the way, but it still arguably made things safer for drivers.