Police accused the 250- strong crowd of showing "contempt" for the safety of motorists after manhole covers and rocks from the roadside were dumped on the carriageway.
The pounds 100m eight-mile stretch of road in Berkshire became the object of a passionate campaign during which a thousand people were arrested.
Marchers taking part in yesterday's demonstration split away from the prescribed route on to the road for about two hours, police said, forcing the closure of the road.
One person was arrested for obstruction of the highway. Police said only about 60 cars were delayed but "extensive damage" was done to the road.
The protesters left after a couple of hours to hold a candlelit vigil at Donnington Castle. The march was intended to highlight the consequences of the bypass, including accidents. They also wanted to raise fears of further building work on nearby greenfield sites, and problems of pollution.Reuse content