NASCAR has adjusted the rules for its new-for-2014 knockout qualifying system amid concerns about the dangers of drivers slowing on cool-down laps.
The previous single-car format was ditched in favour of a Formula 1-inspired method this season.
While broadly welcomed, the new system gave rise to some near-misses at Phoenix and Las Vegas in recent weeks as drivers on flying laps came across competitors driving much slower to cool their engines between runs.
NASCAR has now allowed cool-down units to be used on pitlane between flying laps, provided cars' bonnets remain closed and generators are not plugged in, with two crew members permitted in pitlane to assist.
It has consequently banned the practice of cool-down laps on track as it believes the pitlane allowances should be sufficient.
NASCAR's vice president of competition Robin Pemberton said it had always been likely that tweaks might be required early in the very different new format.
"The qualifying is new to all of us and as we have said over the past several weeks, we are looking at it from all aspects," said Pemberton.
"Following discussions, both internally and with others in the garage area, we moved quickly to make a few revisions that will be effective starting with our two national series events at Bristol Motor Speedway this weekend.
"We believe this will only enhance and improve what has demonstrated to be an exciting form of qualifying for our fans, competitors and others involved with the sport.
"Moving forward we will continue to look at it and address anything else that we may need to as the season unfolds."