Network Rail claims changes to the East West Rail project passing through Milton Keynes will save six months in construction time and £70 million in costs.
A combined project involving Network Rail and the East West Rail is reconnecting Oxford and Cambridge.
Engineers removed a flyover which crosses the busy West Coast main line at Bletchley.
In its place a new structure, on the line between Bicester and Bletchley, is being built, organisers hope it can last for 120 years with minimal future maintenance required.
Instead of replacing the old flyover like-for-like - which would involve closing the West Coast main line below to build five supporting columns in between the tracks - East West Rail project engineers have used modern methods of construction to build a protective ‘box structure.’
It acts very much like a rectangular railway tunnel, removing the need for separate supporting columns and providing a platform for the flyover to sit on.
This means the West Coast main line - which is one of the busiest mixed-use passenger and freight railway routes in Europe - doesn’t have to be closed during the flyover replacement taking place above as the box structure provides a protective, physical barrier.
Mark Cuzner, East West Rail Alliance project director, said: “By working smarter we’ve been able to speed-up the project by around six months.
"At the start of the project, we built a protective wall next to the West Coast main line so we could safely build the box structure during the day when the railway is open, instead of working piecemeal at night-time when the railway is closed.
“Most of the components for both the box structure, and the flyover, arrived pre-built and were simply assembled on site, like a model kit or set of Duplo bricks.
"The simplicity of construction meant we could safely reduce the workforce onsite by 60%, cut the previously-forecast cost by £70m and get the job done six months quicker than planned.”
Network Rail advises that the new track will be laid on top of the structure in the coming months, but didn't specify further.
The old flyover was built in the 1960s and has been deemed unsuitable by rail officials, it was demolished in 2020.
Simon Blanchflower CBE, East West Rail Company chief executive officer, said: “The transformation of the iconic Bletchley flyover has really brought the East West Rail project to life and brings communities from Oxford to Cambridge ever closer to a new, sustainable transport link across the region”