The Green Party is set to seek a two-to-one split on public transport spending versus investment in new roads in government formation talks.
The demand is a key plank of the party's election manifesto and will be a central issue if it enters formal talks with Fianna Fail and Fine Gael next week.
The policy shift would result in a major overhaul of the Government's national development plan which commits to significant investment in new roads.
However, the Greens will insist there needs to be far greater focus on funding for new trains, buses and cycle paths if they are to enter government.
This could lead to major road projects being abandoned in the constituencies of government TDs.
Fianna Fail and Fine Gael's draft policy framework document commits to investing in public transport and electrifying trains and buses but does not set any targets.
The Green Party is not expected to set out any red lines ahead of talks with Fianna Fail and Fine Gael but will look for clarity on a range of issues beyond climate change measures.
Yesterday party leader Eamon Ryan signalled a significant shift in the Greens' position and opened the door to entering negotiations with Fianna Fail and Fine Gael.
Mr Ryan conceded that his party's plan to establish a national unity government was not working and it needed to explore other options.
He said the framework document published by the two parties on Wednesday was not very detailed.
"I agree with a lot of aspects in it in terms of that whole issue about measuring success not just by economic growth but by quality of life. We've been saying that for 30 years - I'd love to see that implemented," Mr Ryan said.
He acknowledged there are different views in the Green Party about entering government but said he was not worried about a potential heave against him.
Mr Ryan said the economic recovery would happen more quickly "if we were really precise and ambitious" with a programme of public housing.
"For us that includes how much of that is going to be cost-rental housing, be specific around the Land Development Agency, are we giving it CPO powers, what is the constitutional change?" he said.
Mr Ryan signalled that a 7pc reduction in emissions a year will be a key issue for his party in negotiations.
"That 7pc target we know that's what the scientists say we have to do and we know we agreed in the climate committee," he said.
"The other two parties have looked at this and we've been talking to them about it so let's be ambitious and be precise."
A Fine Gael source said the Government's Climate Action Plan committed to 3.5pc reduction in emissions a year or 35pc by 2030 through a range of ambitious targets.
"While many speak of the annual targets that should be met, it must be realised that many of the most effective measures require changes in technology or in assets which cannot happen in a single year," the source said.
The EU New Green Deal, which the Government supports, requires states to reduce emissions by 50 to 55pc.
"Ireland supports this and supports delivering net zero greenhouse gas emissions by 2050," the source added.