A spokesperson for the group, who gave his name as Biff, said safety was "paramount" and the protests would not have proceeded if cars did not slow down sufficiently.
"The intention is to enter the carriageway and walk towards the oncoming traffic along the white lines," he said.
"If cars don't slow down and are hurtling along at full speed then we will be on the hard shoulder wearing our hi-vis with the banners.
"We would hope that it slows down anyway.
He added: "We've had feedback that people are frustrated that they spent time in traffic queues.
"This is like a rolling traffic queue, so we'll move, and once they get to the front they will be able to move on.
"We're not planning to stop traffic but it could slow down to five miles an hour.