A cold winter and sizzling summer has forced developers to push back the expected completion date of the A45 link road near Weedon.
In August last year, the project looked on track for a spring 2018 finish but this year's extreme weather has had an impact on construction.
The A45 Daventry development link road will form a new 3.5-mile long single carriageway, which is aimed to improve transport links between Northampton and Daventry and improve access between Daventry and the M1 motorway.
A Balfour Beatty spokesperson said: “We are working closely with Northamptonshire County Council to ensure works to the A45 Daventry Development Link Road continue at pace.
"Despite difficult weather conditions earlier this year, all elements of the scheme are in their final stages and approaching completion.
"The link road is now on track for an early autumn opening.”
The project has long been on Northamptonshire County Council's agenda and it was not until 2015 that the first sod was cut.
Northamptonshire Highways' website states: "Construction commenced on the 18 July 2016, with completion due by September 2018.
"Whilst many aspects of the work have progressed as expected, a number of factors have affected progress including geological and ecological constraints and the need to undertake additional monitoring work.
"The prolonged and very cold winter in 2017, followed by torrential rain in early summer 2018 and the extreme heat during July and August 2018 has also caused unavoidable delays.
"Our principal contractor, Balfour Beatty, are finding it increasingly difficult, because of these weather conditions and external factors, to meet the anticipated completion date and we are now looking at completion in early October 2018."
A spokesman for the county council added: "The A45 Daventry development link road will form a new 3.5mile long single carriageway which will improve transport links between the towns of Northampton and Daventry, and improve access between Daventry and the M1 motorway.
"The project will also relieve communities in Flore, Weedon and Upper Heyford of through traffic as well as supporting future growth in the Daventry district.
"Overall, the scheme is progressing very well, despite the extremely difficult winter with heavy snowfall, prolonged freezing conditions, high winds and substantial rainfall which created very significant challenges for construction activities and inevitably affected timescales for completion.
"The link road is now on course for a completion in the autumn."