The accident in Turn 5 happened when the car of four-time IndyCar champion Franchitti launched over Takuma Sato's and sailed into the fence. Debris was showered into the grandstand from both the cars colliding and the impact with the fence, and Franchitti's badly damaged car bounced back onto the track. E.J. Viso then hit Sato's car.
IndyCar said one series official was taken to a hospital to be treated for minor injuries, and Houston Fire Department spokesman Ruy Lozano said 13 fans suffered injuries, with two transported to hospitals. Franchitti has two fractured vertebra that will not require surgery, a fractured right ankle, and a concussion. He will be held overnight at the hospital.
After the wreck, the caution came out to freeze the field, allowing Penske Racing's Will Power to win the race while halting Dixon's final attempt for a sweep of the doubleheader sweep.
Dixon settled for second. He entered the Houston doubleheader trailing Castroneves by 49 points, but leaves with a 25-point lead going into Oct. 19 season finale.
There was no celebration, though, for Dixon or Power, who raced to his second victory of the season. Both had to drive through the wreckage from the three-car accident and past Franchitti, who sat inside his car waiting for medical attention.
Both drivers said the scene reminded them of the 2011 accident at Las Vegas that killed Dan Wheldon.
"I just saw Dario's car and him sitting in it with a lot of damage, and yes, that's what it reminded me of," said Power, who broke his back in the Las Vegas accident. "I hate seeing that. We try to keep these cars on the ground."
Dixon waved to his teammate and got only a slight head nod back, and team owner Chip Ganassi rode a scooter out to the scene. Franchitti was placed on a stretcher and taken by ambulance to a hospital.
"Dario definitely got into the fence pretty hard," Dixon said. "All in all I hope that he's OK and obviously the fans. The fence took a pretty good hit there."
Dixon needs to only finish fifth or better in California to win his third IndyCar title.
"It's still going to come down to the wire," he said. "It's still going to be the last lap, last corner kind of situation. At least I hope that it ends that way."
Castroneves, who also had a gearbox problem in Saturday's race, finished 23rd. He had started on the pole, got a great jump on the standing start to get past Dixon for the lead, but Dixon was screaming on his radio within minutes that Castroneves' car was leaking oil everywhere and it was splashing onto Dixon's tires and visor.
Castroneves said little to his Penske Racing team, but detected a vibration in his car with every shift of the gears after just a handful of laps. The problem worsened and he came to a complete stop on the course at Reliant Park after just 11 laps.
"It's frustrating and disappointing," Castroneves said. "It hurts. It really hurts."
His car was towed to the garage with a broken gearbox, Castroneves made the long walk back still wearing his helmet, and team owner Roger Penske retreated without comment into a team transporter.
The team eventually replaced the gearbox and Castroneves returned to the track, 36 laps down and needing a miracle in Fontana, where the three-time Indianapolis 500 winner was fastest during an open test last week.
"The racing isn't over, we know that. We've seen this thing go up and down," team owner Penske said. "I think Will's performance today shows the speed the team has in the cars. We've been here before, and we'll go to a track we like and maybe it will bring us some luck."
But Penske said Castroneves will likely have to change his engine before the finale which will incur a 10-spot penalty on the starting grid at Fontana.
"It's a long race and we're going to go for it," said Penske, adding "it doesn't make sense, as far as I'm concerned" that reliability and durability failed twice in two days in a season in which Castroneves had been the only driver to complete every lap heading into Houston.
Dixon said his strategy didn't change when Castroneves pulled over Sunday with his problem. He said he saw Castroneves drive over a bump in Turn 1 under yellow that had caused problems all weekend and it caused some of the underwing to fall off of his car. Dixon said oil began pouring out of Castroneves' car.
"He hit really hard going through Turn 1 kink, instead of sticking to the left there, for some reason he went right in the middle and that's when some of the underwing fell off when he hit that hard," Dixon said. "With the amount of oil that was coming out of that thing, I knew it was pretty terminal.
"But at that point you are thinking you still want to win the race, and Will was being super aggressive and trying to win the race and help his teammate."
Penske praised Power for holding off Dixon for the victory.
"With Will out there battling and taking some points away, he got his job done," Penske said.
Power said his job in Fontana will be to help his teammate.
"Going into Fontana, it's all about Helio winning a championship, so whatever I can do," Power said. "If Helio needs to win the race and I need to be somewhere in between him and Dixon, then that's what we're aiming for."