Michael Phelps DUI

Michael Phelps' SVU was parked on the side of the road near the Fort McHenry Tunnel late Tuesday afternoon. The car has since been moved. (Courtesy of WJZ / September 30, 2014)

Michael Phelps was arrested early Tuesday in Baltimore, charged for the second time in 10 years with drunken driving. The charge comes five months after the record-setting Olympian's return to competition.

Phelps, 29, was stopped for speeding just outside the Fort McHenry Tunnel about 1:40 a.m. Tuesday, Maryland Transportation Authority Police said. He was clocked going 84 mph in a 45-mph zone in his 2014 Land Rover and subsequently failed a standard field sobriety test, police said.

Phelps posted an apology on social media Tuesday afternoon, saying: "I understand the severity of my actions and take full responsibility. I know these words may not mean much right now but I am deeply sorry to everyone I have let down."

Police, who said he was cooperative, also said Phelps failed a Breathalyzer test but would not confirm the results.

The swimmer was charged with DUI, excessive speed, and crossing double lane lines. Police said he was not taken to Central Booking but processed at a transportation authority command station and released to a "responsible adult." His vehicle remained on the shoulder of the road for hours Tuesday before being picked up in the afternoon. The DUI charge carries a possible penalty of a year in jail, though one legal expert said it was unlikely Phelps would get jail time.

The arrest of the decorated Olympic swimmer from Rodgers Forge was another low in a month of bleak off-field stories for Baltimore sports. Earlier in September, the Ravens released star running back Ray Rice after TMZ posted video of him felling his then-fiancee with a punch. The same week, popular Orioles slugger Chris Davis was suspended 25 games for amphetamine use as his team was about to clinch its first American League East title since 1997.

Phelps' agent, Drew Johnson, offered no comment beyond Phelps' Twitter apology. His longtime coach, Bob Bowman, did not respond to a request for comment.

Phelps pleaded guilty to driving while impaired after a 2004 arrest in Wicomico County, when he was 19. He encountered further controversy in 2009, when British tabloids published photos of him smoking a marijuana pipe at a college party.

In both cases, Phelps apologized and promised better judgment going forward. Given his past difficulties, the arrest raised questions about Phelps' dedication to his 5-month-old comeback and about his appeal to sponsors as the leading figure in his sport. Though Phelps hasn't formally committed to swimming at the 2016 Olympics in Rio de Janeiro, he has promised to train more vigorously to improve his results against elite competition.

"To be quite honest, it's like a punch in the stomach," said NBC commentator and former Olympic gold medalist Rowdy Gaines. "I felt like I was going to throw up. I know that sounds a little dramatic, but he's the face of our sport."

Gaines has called almost all of Phelps' significant races and said he'll always support him personally.

"But he's almost 30," he said. "I'm sure he doesn't want to hear it right now, but he needs to know better. … He's so lucky, because he could've ended up killing somebody."

Swimming and Olympic officials also expressed disappointment.

"The news regarding Michael Phelps and his actions are disappointing and unquestionably serious," USA Swimming said in a statement. "We expect our athletes to conduct themselves responsibly in and out of the pool."

Added Scott Blackmun, CEO of the United States Olympic Committee, in a statement: "We were surprised by today's news. We are disappointed on a number of fronts."

Phelps was suspended three months by USA Swimming in 2009 for the photo of him smoking a marijuana pipe. Asked if he might face suspension for this arrest, a spokesman for the governing body did not respond immediately.

Phelps retained his commercial appeal and competitive form through his previous missteps. He has sponsorship deals with Under Armour, Subway and Aqua Sphere, a company for which he and Bowman are creating a new line of swim gear. Phelps has also been a spokesman for brands such as Visa, OMEGA watches, Louis Vuitton luggage and the Hilton hotel chain, among others.

It wasn't immediately apparent how his arrest might affect his existing deals; spokespersons for Under Armour, Subway, Aqua Sphere and OMEGA did not respond to requests for comment Tuesday.

But Phelps will likely remain a popular corporate pitchman, said Bob Dorfman, executive creative director for San Francisco-based Baker Street Advertising.

"A second DUI is going to make sponsors nervous," Dorfman said. "Fortunately for Phelps, the 2016 Games are still a ways off, and there's plenty of time for this to be forgotten before the serious Rio marketing push begins. … As long as he stays squeaky clean and swims well from now to Rio, I don't see this affecting his marketability. His comeback story is simply too compelling to consumers and marketers."