Work on a bypass in Carmarthenshire will not begin until 2025 at the earliest, a letter from Welsh Government says.
Construction had been planned to start on the £50m Llandeilo road by the start of 2019.
Plaid Cymru accused the Welsh Government of breaking a promise made in a budget deal with the party in 2016.
The Welsh Government said it remained committed to the scheme.
Residents in Llandeilo have been calling for action for four decades – the town suffers from congestion from lorries driving through the main street.
The route, which is on the A483, is currently used as a route from Swansea to join the A40 to the Midlands.
Transport Minister Ken Skates had promised “shovels in the ground” by the end of 2019.
Earlier this year it was confirmed work had been delayed until autumn 2022 at least.
But in a letter to the area’s Member of the Senedd, Plaid Cymru leader Adam Price, Mr Skates laid out a new potential timetable for the project, with short, medium and long-term measures.
Constructing a “Llandeilo relief road” is listed as a long-term measure, pegged for at least five years away.
Short-term measures, to be implemented within a year, include new traffic lights, removal of parking and loading bays on Rhosmaen Street and additional public parking.
Medium-term measures would include “footway enhancements”, improved bus connections from Llandeilo railway station and a “Ffairfach relief road” at Ysgol Bro Dinefwr.
Story from BBC.co.uk