IIRC near Paris there are some highways with an extra lane on the far side that is normally outright blocked by barriers that can hinge themselves away in case

IIRC near Paris there are some highways with an extra lane on the far side that is normally outright blocked by barriers that can hinge themselves away in case of heavy traffic. I always wondered what the rationale was to _block_ the lane. Maybe it has to do with speed control (wider, empty roads induce a safety feeling) or an attempt to combat a form of Braess's paradox.