A Plaid Cymru government would invest £6bn in “shovel-ready” projects, the party has pledged.
It says its “rapid recovery” economic package would create thousands of jobs.
The plan will be put into action if the party gains power following May’s Senedd elections.
Projects in the “green economic stimulus” could include thousands of new social homes, greater investment in renewable energy, and more electric vehicle charging points.
Plaid would also offer long-term zero-interest loans “to get businesses back on their feet”.
Part of its plan to pay for the package would involve asking the UK government to increase the Welsh Government’s borrowing powers.
But if the Treasury rejects the request, then Plaid says it would use councils’ powers to borrow money and investment from the new UK infrastructure bank to fund the proposals.
Its “plan B” would also include “appropriate use” of the Mutual Investment Model (MIM) – a funding model developed by the current Welsh Government whereby private partners are awarded contracts to build and maintain public assets.
A project to turn an 11-mile (18km) stretch of the A465 heads of the Valleys road into a dual carriageway between Dowlais and Hirwaun is the first project to be delivered using the MIM.
Delyth Jewell, Plaid Cymru’s South Wales East Senedd member, said the scheme’s eventual cost of more than £1bn was a “waste of public money”.
Plaid leader Adam Price said the “ambitious but deliverable” ideas included in his party’s Rebuild Wales rapid recovery plan should have been introduced years ago had the Labour Welsh government shown “greater urgency”.
Mr Price said: “Within its first few hours, a Plaid Cymru government would announce a £6bn green economic stimulus, creating almost 60,000 jobs through tasking the National Infrastructure Commission with delivering shovel-ready investable projects.
“These could include building thousands of new social homes, retrofitting existing homes, expanding and electrifying the rail network, and delivering the fastest broadband to all parts of Wales,” he added.
The £6bn programme of investment is based on analysis commissioned by the Wales Trades Union Congress, which recommends 16 infrastructure projects over two years.
It suggests the projects could create 59,000 jobs, including 45,500 direct jobs and 13,500 indirect jobs in the supply chains.
Plaid is also promising an initial £50m investment to introduce a “Welsh youth guarantee giving secure employment to every 16 to 24-year-old on at least a living wage”.
People recently made redundant would potentially be able to benefit from a national training programme for workers to reskill.
A trial would be introduced to give people aged over 25 “a lifelong personal learning account’ with an initial tax-free credit of £5,000, and loans for more expensive courses on the same terms as university tuition fees.
Mr Price also promised that a Plaid government would “implement a new ‘local first’ procurement policy to give preference to small and medium-sized local businesses – setting a target of increasing Welsh firms’ share of public procurement from 52% to 75%, creating up to 46,000 jobs”.
