The milestone was reached on Monday, October 21, when a Chiltern Class 168 train made the journey over the newly rebuilt section of track from Bicester to Bletchley.
Network Rail and Chiltern Railways worked together to operate the first train on this section of line, which has been closed for nearly 60 years.
The test train left Oxford station at 9.43am and travelled via Bicester, Winslow, and Bletchley before arriving at Milton Keynes Central at 10.25am.
The entire journey took 42 minutes and saw the train reach speeds of up to 100mph on several sections of the line.
It was part of the East West Rail project, which aims to deliver transport connections for communities between Oxford and Cambridge.
Network Rail’s director of capital delivery, Christian Irwin, said: “Today is a huge milestone for the East West Rail project.
“I am incredibly proud of the partnership between Network Rail, our East West Rail Alliance supply chain partners, the Department for Transport, East West Rail Company, and Chiltern Railways, in successfully completing the construction and entry into service of the new railway between Bicester and Bletchley.
“The running of our first test train today is a huge achievement and brings us one step closer to restoring train services between Oxford and Milton Keynes for passengers.”
Chiltern Railways’ programme director, Rianna Stanwell, added: “I am delighted that Chiltern will be running the first series of test trains between Oxford and Milton Keynes.
“Working with colleagues at Network Rail and the East West Rail Alliance, this important step in the programme will ensure the infrastructure is ready for passenger service in the future.”
Connection Stage One of the East West Rail project includes the introduction of services from Oxford to Bletchley and Milton Keynes, with the aim of the first passenger services starting in 2025.
The services are expected to better connect passengers and help unlock economic growth, creating new opportunities across the region.
East West Railway Company’s CEO, David Hughes, said: “This is a fantastic achievement and an extremely proud moment for everyone here at East West Rail.
“We can all now look forward to passenger services beginning next year and delivering the improved connectivity which this region so desperately needs.”
Chiltern Railways is running test trains as part of technical preparations to open the line.
Testing and training will continue over the coming months, with further test runs to ensure the safety and reliability of the new infrastructure.