This is part of the new plan for pedestrianisation of London Road during weekends*. It makes the cafes on London Road much more peaceful.

It is closed from Manor Mount to Barclays so you can still slip down Davids Road to avoid traffic jams on Dartmouth or Devonshire Roads.

* Only kidding, it just seems to be temporary. I'm not sure what they are doing but it seems to be focused on the pedestrian crossing.