A Fathers 4 Justice campaigner dressed as Batman caused lengthy queues on the M25 around London before being arrested just before the evening rush.
Geoffrey Hibbert, 48, of Farnborough in Hampshire, spent seven hours on a gantry near Heathrow Airport.
He came down from his perch at Junction 14 on the road to Terminal 5 just after 1600 BST.
Police said despite the massive traffic disruption on the motorway, the man had the right to protest peacefully.
A Metropolitan Police spokeswoman said that despite queues that stretched for 19km (12 miles) on the M25 and 32km (20 miles) on the M4, the decision to allow the man to stay on the gantry all day was made by the senior officer at the scene.
"He has the right to protest peacefully. It is entirely a matter for the senior officer," she said.
Police had initially said the protest caused no tailbacks or lane closures.
'Protest all day'
A Highway Agency spokesman said: "We had delays at one point of 94 minutes and we did our utmost to get the message out to the public to get people to take alternate routes."
The agency received permission from police to reopen two of four lanes on the motorway a couple of hours after the protest began shortly after 0800 BST.
Speaking by mobile telephone, Mr Hibbert told the BBC: "I'm doing this for my daughter. I'll do my protest all day."
Fathers 4 Justice protesters have staged a series of high-profile stunts across the UK, normally involving clambering on to a landmark dressed as superheroes such as Batman, Spiderman or Superman.
They are calling for more rights for fathers affected by issues involving access to their children after divorce.
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