A redesign of the Metro Link which would avoid closing a road in Beechwood would cost 35 million euro.
Building Dublin's first underground involves upgrading the Luas green line on the southside.
The plans are online for people to have their say, and locals in Beechwood have voiced opposition to the proposed closure of Dunville Avenue to Beechwood Road.
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It links Rathmines and Ranelagh and would force drivers to divert through Ranelagh Village which has some of the worst bottlenecks in the city.
The NTA is proposing two alternatives - a bridge, or a cutting to allow for trains to travel under the road.
However according to The Irish Times, that would add 25 to 35 million euro to the 3 billion euro budget.