The alterations are the start of work to create one-way systems around the city and a car free square by County Hall.
Today the one-way system on St John’s Square has been reversed, meaning traffic will have to travel anti-clockwise around the square.
The entrance road into St John’s Square leading to Hodgson Street remains two-way.
Also, the barrier at the end of Margaret Street has been removed for traffic to join the new system onto the square.
But there is no right turn from the square onto Margaret Street.
Changes began on Monday and motorists can no longer make right turns from Northgate into Westfield Road next to QEGS.
And a new right turn into this area has been put in from Marsh Way onto Saville Street.
Further changes to the city centre roads will take place at the start of January. See this week’s Express for details.