The Associated Press has learned that NASCAR is making changes to qualifying after drivers expressed safety concerns.

During a conference call Tuesday with crew chiefs, NASCAR banned drivers from making cool-down laps following their qualifying attempt. Teams will instead be allowed to hook up cooling units to their engines through hood flaps.

NASCAR this season moved to a new knockout qualifying format widely praised as more entertaining. Drivers say the new rules prohibit cooling the engines on pit road, forcing them to circle the track at slow speeds at the same time other drivers are speeding past during their qualifying attempt. Brian Vickers called it "the most dangerous thing" he's ever done in racing.

Several people who participated in Tuesday's call told the AP that NASCAR initially said teams could use external fans on pit road to cool the engines. But after nearly unanimous objections, NASCAR relented on the use of cooling units.

The people spoke on condition of anonymity because NASCAR has not formally announced the changes.