A section of Liverpool Road had been closed temporarily for the final construction work on the new bypass, which opened earlier this month.
It meant people were forced to use rat-runs through Penwortham to reach Liverpool Road, causing extra traffic on residential roads and along Cop Lane. It also caused problems for bus users, with some stops in the Cop Lane and Liverpool Road areas not serviced.
But now people are able to once again travel between Penwortham and Hutton along Liverpool Road, and access John Horrocks Way from the Howick Moor Lane side.
County Councillor Keith Iddon, Cabinet member for highways and transport, said: "Following the opening of John Horrocks Way earlier this month, we introduced the temporary closure on Liverpool Road for the final junction work.
"We know that this was disruptive and led to increased traffic on some parts of the network. We're sorry for the disruption caused to your journeys during this work.
"The temporary closure could only be carried out once the new bypass was open, otherwise it would have led to even bigger traffic issues on the network.
"The important thing for local people is that Liverpool Road is open once again, providing a route to and from Penwortham, and providing a new junction with John Horrocks Way.
"We’re pleased that our highways team have been able to deliver the work on the new road ahead of schedule, so that people can now benefit from the new road."
The aim of the new bypass is to reduce unnecessary traffic through the centre of Penwortham, which will particularly benefit local people and public transport.
Traffic signals will be monitored to check that they are working effectively, now that the construction work has finished.
There are no plans to reopen the slip road onto Guild Way, as this would affect the new flow of traffic along Golden Way towards Preston. It is part of the wider measures to encourage people to use John Horrocks Way, rather than travelling unnecessarily through Penwortham.
The new bypass is one of the major road schemes as part of the Preston, South Ribble and Lancashire City Deal.
This is an agreement between the Lancashire Enterprise Partnership, Preston City Council, South Ribble Borough Council and Lancashire County Council, along with central government and Homes England.
Councillor Bill Evans, Cabinet member for planning, regeneration and City Deal at South Ribble Borough Council, said: “The opening of John Horrocks Way is an important milestone in improving the highways infrastructure in South Ribble. The opening of the junction at Howick with Liverpool Road is welcomed and will ensure that local traffic is able to take full advantage of the new road.”
The City Deal will help to create more than 20,000 new private sector jobs and see over 17,000 new homes built across the area, along with new school places, open green spaces and new health provision to cater for the growing population.