INDIANAPOLIS -- Marco Andretti made the most of a strong tow, Graham Rahal took lessons from an unwitting Tony Kanaan and Ryan Briscoe avoided trouble.

Yes, things are starting to bustle in Indianapolis.

Tuesday was the busiest opening day of Indy 500 practice in nearly a decade, and the key to staying on the track was more about handling heavy traffic than going fast.

Andretti, who posted the best lap of the day at 226.599 -- more than 1.3 mph than his teammate Kanaan, was one of the fortunate ones.

"I caught the traffic just right, thanks to Graham Rahal for that," Andretti said. "I only did like four runs myself, so I was definitely lucky."

Danica Patrick, another of Andretti's teammates with Andretti Green Racing, wasn't as lucky.

At one point, she slowed her car by nearly 15 mph to avoid getting into trouble, and later managed to turn in a fast lap of 224.095, the ninth best of the day. Not bad, considering it came during warm track conditions and amid the struggle to free herself from other drivers.

Even the rookies, who had spent Monday and Tuesday practicing by themselves, noticed how much of a difference the extra cars made.

"It seemed pretty busy out there," said Rahal, the 19-year-old who won at St. Petersburg last month. "Obviously, it's not as busy as it's going to be. At one point, it seemed like everyone wanted to put a lap in."

In all, 33 cars went around the 2.5-mile oval Tuesday, completing a total of 1,385 laps. The last time that many cars drove on opening day was 1999.

Now, the same drivers may have to get accustomed to working this way.

There are already 34 car-driver combinations vying for 33 starting spots in the May 25 race and more drivers are expected to have rides before the fourth and final day of qualifying May 18.

The forecast isn't helping, either.

Rain threatens to wash out at least part of practice Wednesday and Thursday, and could complicate the work teams hope to complete before pole qualifying begins Saturday.

"The weather is something that is going to affect everybody," Kanaan said. "The cooler it is, the more down force we have. It's going to be tough to set up the car."

If it's dry, drivers are likely to take as many laps as they can because of the threat of rain, forcing many teams to replay the scenario that unfolded Tuesday when rookies and veterans ran side-by-side for the first time, sometimes treacherously.

"I ran into one car doing a sticker on my second flying lap," Patrick said. "He was really slow through (turns) three and four."

Not everyone had the same problems.

Rahal spent part of the day following Brazil's Kanaan, the former IRL series champ and a former pole-sitter at Indy. Kanaan had a fast lap of 225.269, and Rahal tried to keep up with him even if Kanaan was unaware he had become Rahal's unofficial mentor.

"It helps to follow guys like Tony Kanaan around the track," Rahal said. "You can learn from them."

Last year's series runner-up, Scott Dixon of New Zealand, was third at 225.011 and Australian Ryan Briscoe was fourth at 224.804.

Former Indy winners Helio Castroneves of Brazil, Dan Wheldon of England and Buddy Rice all were in the top eight.

"We finished in the top six, so I'm happy with our results," said two-time race winner Castroneves, who went 224.576. "We're putting the pieces together, and by the end of the week, hopefully, we'll be where we need to be."

Another complication could be the large contingent of rookies.

If all of the first-time drivers make the starting grid, it would be the largest rookie field since 1997, and most of them are still getting used to driving either ovals or contending with Indy's tricky conditions -- or both.

To veterans, it can be every bit as dangerous staying out of trouble as it is for rookies.

So some teams, like Penske Racing, ran counter to the conventional wisdom.

"We sort of eye it out before hitting the track," said Briscoe, Castroneves' teammate with Penske. "Hitting the track this morning, there were not a lot of cars, and it definitely helped. You're going to get traffic sometimes, and this afternoon, that's what he had to go through somewhat."

But there is one advantage to driving amid all those cars: Finding speed, with a little help from a friend.

"I think today we were running about 222s," Rahal said. "I think that's pretty good. Some of those speeds are not real, like Marco's. I know because I was the guy who gave him that tow."