Delays are affecting traffic travelling westbound on the M4 between junctions 7 and 8/9 near Maidenhead.
A police spokeswoman said there was a collision between vehicles, but no one was hurt.
The damaged vehicles have been moved to the hard shoulder but traffic is still moving slowly.
Top Ten Articles
An extra £20,000 looks set to be allocated by the Royal Borough to fund a legal fight if Heathrow Airport is given permission to expand.