A temporary roundabout has been put in place at the Victoria Ave and Dublin St intersection as the traffic lights are upgraded.
The roundabout was installed on Monday. The old traffic lights will be removed over the next few weeks.
The $150,000 project is expected to be done by the end of next month.
Whanganui District Council senior roading engineer Brent Holmes said the intersection's traffic equipment was out of date and had become unreliable.
The basic existing layout will be retained but lane alignments improved. A new raised pedestrian/cycle platform crossing will be installed across the left-turn slip lane from Dublin St into Victoria Ave.