Providing a "dynamic" bus station in Cardiff will be central to the success of the South Wales Metro project, a transport expert has warned.
University of South Wales' Prof Stuart Cole believes proposals could make it too small, saying buses must link easily with trains across the network.
Cardiff's new bus station was due to open in December but was redesigned and delayed amid funding concerns.
A council spokesman said a date for construction to start has not been set.
However, he said when construction begins it will take a maximum of two years to build.
Prof Cole wants to see commuters able to transfer seamlessly from nearby Cardiff Central train station.
But he said: "The latest plans are to reduce the number of bays from 25 to 14. This could make it overcrowded and cause confusion.
"It needs to be dynamic, making it easy to transfer from trains and between buses."
Andrew Potter, Wales chairman for the Chartered Institute of Logistics and Transport, said it is crucial "all the pieces fit together" for the metro.
He said: "There are many new housing developments cropping up around Cardiff.
"Everyone lives relatively close to bus stops but not train stations."
Paul Swinney, principal economist for the Centre for Cities think tank, said: "What's more important, a metro-type [light rail system] or better buses?
"The question is, how do you get places more connected? There needs to be a frank conversation on the most appropriate mode."
Four bidders - Abellio, Arriva, KeolisAmey and MTR - have been in discussions with the Welsh Government since June 2016 about the next Wales and Borders rail franchise, which will include the metro.
They will soon submit final tenders for the delivery of the £600m project from October 2018.
To make it "transformational", Prof Cole believes it must be inspired by European networks that have taken tens of thousands of motorists off the road.
He pointed to Bordeaux, where 40% of people left their cars at home when the system opened.
"In the Netherlands, deregulation - meaning a single ticket can be used on trains, trams and buses - has seen Utrecht get about 70% of commuters on public transport or cycling," he added.
"A similar system is essential in south Wales, but pivotal will be dynamic bus stations close to train stops so users can hop on and off."
The saga in Cardiff began when the former bus station was demolished to make way for Central Square in 2015.
Original plans for a nearby replacement was for it to have 25 bays.
But slimmed-down proposals include provision for 14, with Prof Cole believing this will cause confusion as services will leave from different bays each time and some from roads outside.
Making people fully aware of departure points, therefore, will be crucial, he said.
"Most metros have very good directional information. How to get people using public transport and not cars is to make journeys really easy in cities," Prof Cole added.
"You need information screens, the system should be so sophisticated and simple in station and on buses."
A Cardiff council spokesman said the station will be easy to navigate, with destinations grouped so buses going to a location will always leave from the same area.
He added: "Extensive modelling confirms that the proposed number of bays will accommodate at least as many departures per hour as the old bus station prior to its closure.
"It was never the case that all city centre services used the old bus station and there will be continued use of existing on-street stands."
The spokesman also said real-time information displays showing departures from the station and street will make it easy for commuters transferring from train.
Plans also include an interchange lounge, that will eventually link to central train station.
While cabinet has approved plans, the developer has to fill the upper floor to make the scheme viable - with offices or student accommodation options.