Consultants have advised the Wellington Regional Council that the capital's bus services will continue to worsen unless Manners Mall is opened up.
A proposal to allow buses to use the mall, which has been pedestrian-only for the past 30 years, has met with such heavy public criticism that it has been put back out for further public consultation.
In the meantime a study by the consulting firm Opus International has found that peak-hour public transport flows between the railway station and Courtenay Place are expected to grow by up to 30% by 2016.
Congestion between Taranaki and Willis streets is worsening, the study says, and will continue to do so unless changes are made.
Manners Mall lies between those two streets.
Opus trialled three scenarios before concluding that opening the mall to buses would be the most effective way of improving journey times and reliability.