Officers did not administer field sobriety tests because Phelps showed no signs of being impaired by alcohol, police spokesman Anthony Guglielmi said. Police were aware of Phelps' 2004 conviction for drunken driving and did not give him special treatment, Guglielmi said.
"We had our very best eyes on the situation, and we're very well aware of his history and his notoriety," he said. "We wanted to make sure that everything was done completely by the book."
Phelps, 24, told police he drank a beer around 7:30 p.m. and left his house about an hour later, according to a police report. The accident occurred around 8:45 p.m., shortly after he left Baltimore's train station with two passengers, the report said.
The swimming star will be cited for driving without a license and failure to establish residency in Maryland, Guglielmi said. The citation carries no fine, but Phelps will have to appear in court and explain why he did not have a valid license.
Phelps presented officers with a Michigan driver's license, according to the report, and investigators determined it was invalid after consulting with Michigan authorities. Phelps lived in Michigan between the 2004 and 2008 Olympics and moved back last year to his native Maryland.
Fred Woodhams, a spokesman for the Michigan secretary of state, said Friday night that Phelps had not paid a fee to reinstate his license, which had been suspended because he was late paying a different fee for not having proof of insurance in 2006.
"It could very well be something that just slipped through the cracks," Guglielmi said of the license.
Phelps' agent, Drew Johnson, and his coach, Bob Bowman, did not respond to repeated messages seeking comment.
According to the report, the driver of a Honda Accord, Amanda E. Virkus of Sandy Spring, ran a red light at the intersection of two one-way streets north of downtown. Phelps' Cadillac Escalade sport utility vehicle crashed into the driver's side of her car.
Virkus, who also showed no evidence of being impaired by alcohol, will be cited for failure to obey a red light and causing an accident. Those citations carry a maximum penalty of a $180 fine and three points on a driver's license, Guglielmi said.
Phelps' Escalade had a crumpled front hood after the collision, while Virkus' car had considerable damage to the front driver's side. Two parked cars also sustained minor damage, and one of them was occupied at the time, according to the report.
Phelps told police his right ankle hurt after the crash, but he did not seek treatment. His passengers were uninjured. Virkus was treated at a local hospital for back and neck pain and released. A woman sitting in one of the parked cars was not hurt.
Virkus' mother, Kathy, said her daughter was hit pretty hard in the crash. She referred other questions to her daughter, who was not home.
Onlookers quickly gathered after the crash and snapped photos of Phelps and his vehicle.
Phelps pleaded guilty to drunken driving in 2004, shortly after he won six gold medals at the Athens Olympics, and was sentenced to 18 months' probation.
"Getting into a car after anything to drink is wrong. It's dangerous and unacceptable," Phelps said after his 2004 arrest.
Earlier this year, USA Swimming suspended Phelps after a British tabloid published a photo of him using a marijuana pipe. The Richland County, S.C., sheriff's office investigated the photo but found there wasn't enough evidence to charge Phelps, who apologized for his behavior.
Phelps has won a record 14 gold medals, including eight at last year's Beijing Olympics. He recently returned to Baltimore from the world swimming championships in Rome, where he won five golds and a silver.
John Cadigan, a senior coach with the North Baltimore Aquatic Club, which is based at the swim center operated by Phelps and his coach, said Friday that Phelps was not expected to be back at practice until next week.
Associated Press writers Kasey Jones in Baltimore, Aaron Morrison in Sandy Spring, Md., and Paul Newberry in Atlanta contributed to this report.