He spoke as An Bord Pleanála considers a planning application from the port company that would double the volume of trade it handles over the next 15 years.
Mr Ryan said the plan would add 2.5 million truck journeys to an already choked M50, and was designed for an increase in consumption on a scale he did not believe was necessary or sustainable.
Mr Ryan has made his views known previously on the €1.1bn project which Dublin Port calls 3FM – the third and final part of its 2040 development masterplan.
However, the TD repeated his concerns at a public meeting he convened in his Dublin Bay South constituency where the sites for the proposed work are located.
He said that, as Transport Minister, he could not intervene in the planning process but he wanted to share his thoughts on the proposals.
He reminded the attendance that the deadline for submitting observations to An Bord Pleanála was September 25.
A spokesperson for Dublin Port said the company had stated its position in its planning application and would not be making additional comment.
The port handles 35 million tonnes of goods annually but wants to increase its capacity to 77m by 2040.
It has already increased the number of berths and is working on a new jetty.
The final phase of the expansion would create more roll on, roll off capacity, extra space for container ships to load and unload and a large container and trailer park.
It would have a ‘maritime village’ to replace rowing, sailing and boat club facilities that would be removed to make way for an access road, and 7km of cycle path are promised along with a few hectares of parkland.
Mr Ryan said the plan was well-designed but he did not see the need to provide for a doubling of trade.
“Our population will grow so we do need to provide for that expansion but what will we be consuming twice the amount of in 2040?
“Maybe 25pc more, maybe even 50pc more but double? I don’t think so.”
He said some imports would fall by 2040, such as oil and other fossil fuels, while compliance with circular economy targets would mean reusing materials, not importing more.
Mr Ryan said there was a need for more balanced regional development and other ports could provide additional capacity.
He also said Dublin Port should be planning to develop rail freight rather than continuing movement of goods by truck.
He said Area O, a 13-acre site proposed for container and trailer storage, should be given up as a nature reserve.
And he said a 10-acre site at East Wall, used to store newly imported cars, should be handed over for housing.
An Bord Pleanála is due to make a decision on the proposals by next February.
