The Welsh Government has given the new Dyfi Bridge on the A487 north of Machynlleth the go-ahead.
The £46m new development will be a viaduct across the floodplain and a river bridge across the Afon (river) Dyfi approximately 480m upstream of the existing bridge.
Transport minister Ken Skates said that with climate change increasing the risk of flooding the bridge would provide protection for homes and businesses.
The current Dyfi Bridge is a 19th century stone narrow bridge with poor visibility and no footways and the river Dyfi frequently floods, severing communities on either side of the bridge. Officials said such incidents are likely to increase because of climate change.
Mr Skates said: ‘The A487 is a key route between North and South Wales linking Gwynedd, Powys, Ceredigion and Pembrokeshire. It is also an important local route providing access to the amenities and services of Machynlleth.
‘We are already making improvements further north with the Caernarfon and Bontnewydd bypass and it is clear to me that action needs to be taken to improve this section of the A487 so that there is a safe and reliable route linking the communities around Machynlleth, including better and more reliable access to bus and train services in the town.’
The scheme will include traffic calming and improved drainage on the A493 immediately north of the bridge to protect the existing cottages, and a flood bund will be constructed to protect the Dyfi Eco Park from river flooding.
Officials said the removal of large scale traffic from the old bridge and provision of a walking and cycle path will improve active travel opportunities increasing the attraction of Machynlleth and surrounding area as a tourist destination.
The next stage will include detailed design works and further ground investigation work. Construction could begin in the summer, subject to the statutory process, with completion by summer 2022.