Ahead of this weekend's Folds of Honor QuikTrip 500 NASCAR Sprint Cup Series race at Atlanta Motor Speedway, the teams and one designated driver apiece got the opportunity to hit the track for some test runs on the the 1.54-mile quad-oval circuit.

It's the first open test of the year, after NASCAR introduced new restrictions on when and how many times Cup teams can test in 2015. And after the season opener last weekend at Daytona International Speedway, it's also the first time that the drivers have been able to hit the track to try out the new rules package for non-restrictor plate events.

The new specifications for 2015 include less horsepower and downforce, and drivers will be able to adjust their track bar setting from within the car during a race event.

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Ganassi's Jamie McMurray was fastest in the first hour and 45 minute run with a best time of 28.943s (191.549mph), while Jeff Gordon paced the field in the second session which lasted just under two hours. With the conditions getting warmer, the later times were slower than those that had been set earlier with Gordon's best clocking in at 29.423s (188.424mph).

See full Atlanta test times

Greg Biffle was one of the few drivers to improve between sessions, his speed picking up from 185.536mph to 186.975mph as he settled in during the day. "My car didn't feel hugely different," he said. "I could tell it's got less power, but it wasn't like 'Oh my gosh, this is a whole different car.'"

NASCAR's senior vice president of innovation and racing development, Gene Stefanyshyn, was in attendance to review the data being collected by the teams, although he admitted that it was a fraction of the information they would get from the upcoming races themselves.

"As we get into our races, we will be collecting, harvesting the data off of the race, and that's really where we know what's going on. In practice, you don't have the same situation as in a race environment," he said. ""Realistically, you probably need five or six races of data points under your belt to draw any significant conclusions."

This week's Atlanta test was open to all teams who could nominate one driver each. Joe Gibbs Racing used the opportunity to give David Ragan his first chance to settle into the race seat in the #18, which he will be in charge of while Kyle Busch recuperates from injuries sustained in a heavy accident in the Xfinity Series support race at Daytona last Saturday.

"The day was great, really uneventful," Ragan reported. "Just learning the Joe Gibbs racing bunch and their process, how they conduct business on a practice day, so we were fortunate to have a few hours today where we can hot lap our M&M's Camry and just enjoyed getting to the race track. It had been a busy week and working through a lot of the details."

"Atlanta Motor Speedway is one of my favourite tracks for a lot of reasons," he added. "The race track's in great shape. It's got a lot of speed. The tyres fall off throughout the run, so a lot of characteristics that makes it fun to drive. The weather worked out just perfect, and it was a lot of fun for sure."

Camping World Truck Series champion Matt Crafton stood in for Busch last weekend in the Daytona 500, but during the week JGR entered into negotiations with Front Row Motorsport to secure Ragan' services as a longer term substitute while Busch is sidelined.

"It all really happened quick Monday night and Tuesday to be down here a day early for a practice session. A lot of the people involved had to have some give and take and it worked out great," said Ragan.

"I'm grateful for the opportunity to get in one of the premier rides in our sport for a little while to see where I stand in my career as a driver," he added. "It's been a few years since I've been with one of the larger teams. I'm grateful that all the parties really worked hard. It all came together to benefits us in a lot of different ways."

Busch himself had been transferred from hospital in Daytona to a facility closer to his home in Charlotte, South Carolina. After an initial surgery at the weekend to stabilise a compound fracture to his right leg, the 29-year-old driver underwent a second surgical procedure to address the mid-foot fracture in his left foot.

A JGR press statement said that the surgery had been performed by Dr. Robert Anderson of OrthoCarolina on Wednesday, and that Busch had spent Thursday night resting comfortably under observation in hospital before being discharged on Friday morning to continue his recuperation at home. There is currently no timeline or prognosis about just how long Busch will be out of competition and how much of the 2015 Cup season he will miss.

"[I'm] really just taking it race by race," said Ragan. "I'm sure over the next few weeks we'll get a better feel for the timeframe for Kyle's return and what the expectations are for going forward for the second half of the year."

See full Atlanta test times