I've found out why they have sealed off the Rutland Street/Halford Street/Queen Street junction!
Halford Street pedestrian improvement schemeIt's not clear what it means by "public space". They are using a different pattern for the proposed pedestrianised bit of Halford Street between Charles Street and Yeoman Street, so maybe it won't be pedestrianised? But it's a bit hard to see how you can have a crossroads be a public space. Additionally, the line of the indicated space seems to indicate traffic would have to turn round.