Eight people were arrested during a protest against work to widen a stretch of the M1 motorway in South Yorkshire.
The protest did not cause any traffic delays, police said
The group of Climate Camp activists had tried to stop work on the M1 widening scheme between junctions 31 and 32 by locking themselves to machinery.
A group spokeswoman said it wanted to "highlight the cost to the climate that road widening brings".
Three women and five men were arrested on suspicion of committing public order offences and later released on bail.
Police said the demonstrators were arrested before they could stop any work and the incident did not disrupt traffic.
The work will see the road widened from three lanes to four and will be carried out within the existing boundaries of the M1.
Campaigner Lucy Wainwright said: "Tony Blair has claimed that the government is taking climate change seriously but billions of pounds of taxpayers' money is now being wasted on a scheme that will do nothing to ease congestion but will increase emissions.
"There are much more effective and economic ways to tackle congestion such as improving public transport and transferring freight on to the railways."
When work began in January, roads minister Stephen Ladyman said: "Widening this section of motorway will support the major improvements that are under way on the M1, helping to ease congestion on this route, one of the busiest stretches of motorway in England.
"The project will only use land within the existing motorway boundaries, enabling us to deliver the benefits rapidly with minimum disruption to drivers and local communities."
Ch Insp Jason Harwin, from South Yorkshire Police, said Monday's protest had not disrupted the motorway.
"The aim of our operation is to ensure public safety in what is a potentially hazardous environment." he added.