The two drivers were helping Goodyear test tires on the remodeled speedway when Biffle apparently blew a tire, causing him to hit the wall between the first and second turns. The accident broke the fuel pump and caused his Ford to burst into flames.

Busch, who was trailing Biffle at the time of the accident, jumped from his car and helped Biffle to safety.

Although Biffle was uninjured, he did not continue the session.

"That was a really hard hit and we lost a good car, but I'm OK," Biffle said.

A track spokesman said Biffle was released from the care center, and left the race track driving his own car.

Biffle was scheduled to attend the Busch Series banquet at Walt Disney World on Friday evening, but the driver flew home to North Carolina and was going to wait to see how he felt before traveling to Florida.

Goodyear tested tires Wednesday and Thursday at Las Vegas, which added 20 degrees of banking this year. The tire company must find the correct compound to bring to a NASCAR-sanctioned test at the track in late January, and the Nextel Cup event there in March.

Busch completed the test and said he liked the track alterations.

"There are a lot of neat characteristics to the track," said Busch, a Las Vegas native. "It's still pretty wide and a great racing surface. It's wide enough that we'll be able to run two and three wide. The transitions from the corner to the straightaways and then the straightaways to the corners are awesome."