Climate protesters have blockaded the M25 during rush hour traffic for the fourth time in little over a week.
Members of Insulate Britain blocked slip roads and the M25, glued themselves to the road and poured paint on the carriageway.
Hertfordshire Constabulary said officers were called to reports of demonstrators near J18 (Chorleywood) of the M25, where "several" people had glued themselves to the carriageway, where they arrested 13 people. The road has since partially reopened.
Officers were called again three minutes later to reports of protesters near J4 (Stanborough Interchange) of the A1M. A total of 16 people were arrested there, the majority of which had glued themselves to the carriageway. A diversion is in place.
Kent Police said 12 people were arrested before they were able to disrupt the carriageway there.
Traffic cameras of the M25 anticlockwise near Watford showed traffic piling up across the three lanes shortly before 8.40am on Monday.
Images from the protests show people sitting on the ground holding signs saying "Insulate Britain" with blue paint splattered across the road and a painted heart on the ground.
A statement from Insulate Britain said: "Early this morning, Insulate Britain blocked the M25 for a fourth time.
"Actions will continue until the government makes a meaningful commitment to insulate all of Britain’s 29 million leaky homes by 2030, and all social housing by 2025.
"People blocked slip roads and the M25 carriageway itself in a number of locations. Once again, blue paint was poured onto the road, which will require cleaning, leading to further disruption.
"Many of those blocking the roads today have participated in all four actions to date."
Chief Superintendent Nick Caveney said: "Protestors have made it clear that they intend to continue causing disruption. Not only is purposely blocking a highway incredibly dangerous, it also affects thousands of members of the public who are stuck in delays as a result.
"We have robust plans in place in order to minimise any disruption and to allow us to make arrests as quickly as we possibly can."
He added: "Officers were on the scene within minutes of being alerted to protest activity, allowing us to put diversions in place to ease the traffic and to make numerous arrests.
"All protestors involved in this morning’s protests have been arrested and will be taken to custody.
"I understand and appreciate the frustration regarding the considerable delays and inconvenience that has occurred as a result of the protests.
"We have now made a total of 76 arrests in relation to protest activity across Hertfordshire over the last week. Please be assured that a full investigation is underway, and we are in the process of gathering evidence in order to ensure that those breaking the law are brought to justice."
Ahead of the action on Monday the group wrote to National Highways and the police to call for speed limits to be reduced and to alert them.
Earlier on Monday morning Foreign Office minister James Cleverly said the protesters were "adding nothing" to the cause of tackling climate change.
Mr Cleverly told ITV’s Good Morning Britain: "It is a completely inappropriate way of making the point they’re trying to make, and I know the police have been taking action, the Home Secretary has made it very, very clear that they should be taking action, the police should take action when people are taking part in criminal behaviour, and that’s what I think everybody will expect."
He said: "I think the vast, vast majority of people want to see us tackling climate change, we are tackling climate change, the UK is one of the global leaders in this and this is very much what the Prime Minister will be taking with him as a message when he goes to the United Nations, or now that he’s at the United Nations General Assembly.
"We’ve got the fastest reduction of emissions of any major developed economy, the UK is actually a real leader on this.
"So I have to say, my belief is that those disruptions and protests are more ego-driven, rather than issues-driven. And I would strongly urge the people involved in it not to put themselves and others at harm by this continued disruption."
He added: "These protesters are waking up at lunchtime and claiming credit for the sunrise. The simple fact is the UK is already pushing the world to do more and we are walking the walk as well as talking the talk and these protesters are adding nothing to that discussion."
Home Secretary Priti Patel is said to have told police to take "decisive" action to crack down on the "selfish" protests.
Transport Secretary Grant Shapps previously said of the demonstrations: "This is dangerous and counterproductive. We all agree that climate change must be tackled, but this sort of behaviour achieves nothing, puts drivers at risk and increases pollution. I expect the police to take swift action to clear the roads."