Prince Philip. PHOTO: AFP
Queen Elizabeth II's husband pulled out onto a main road last month, hitting another car and flipping his Land Rover.
The incident happened near the monarch's private Sandringham estate in eastern England, where the couple traditionally spend the winter months.
One woman in the other vehicle, a Kia, broke her wrist and the other cut her knee. A nine-month-old baby in the back seat was uninjured.
The Crown Prosecution Service said no further action would be taken against the prince.
The Duke of Edinburgh gave up his driving licence on Saturday, which the CPS said was a factor in its decision.
Chris Long, the chief crown prosecutor for the CPS in eastern England, said prosecutors had "carefully reviewed" material submitted by police over the collision.
"We took into account all of the circumstances in this case, including the level of culpability, the age of the driver and the surrender of the driving licence.
UK's Prince Philip, 97, back driving - without seatbelt
"We have decided that it would not be in the public interest to prosecute.
A Buckingham Palace spokesperson said: "The Duke of Edinburgh respects the decision."
Prince Philip apologised in a letter to the passenger of the other car, Emma Fairweather, 46, saying he was "deeply sorry" about her broken wrist.
"I would like you to know how very sorry I am for my part in the accident," said the letter, dated January 21 and revealed by Fairweather to the Sunday Mirror newspaper.
"The sun was shining low over the main road... I can only imagine that I failed to see the car coming, and I am very contrite about the consequences.
"I was somewhat shaken by the accident, but I was greatly relieved that none of you were seriously injured.
"I wish you a speedy recovery from a very distressing experience."
The duke was pictured driving a replacement Land Rover — without a seatbelt — two days after the crash. Police said the royal patriarch was given "suitable words of advice".
The accident stirred up a debate about the elderly and driving in Britain, where there is no maximum age limit.
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