CONGESTION charging will have to be introduced to obtain value from the multi-billion euro spend on new roads and public transport.
And planned extensions of rail and light rail will provide an alternative to the car to just a "fraction" of commuters.
The ESRI also says it is "not clear" if the necessary planning has been undertaken to ensure the benefits accruing from public transport are realised.
"In addition, the ability of the public administration to manage and implement very large projects in a very tight time scale has yet to be proved," it says.
The ESRI assumes that cycling and walking will continue to decline and that the additional demand for motorised transport will be met by public transport.
As fuel rises in price, and a carbon tax is introduced, there will be a demand for small-engine cars.
A switch to moving freight by rail is unlikely over the next 20 years because of the "limited capacity" of the rail network.