Engineering works will be carried out on the Great Eastern Main Line on weekends from January 31 until March 22, at Colchester, Marks Tey, Witham and Chelmsford.
The work involves two kilometres of track installed at Colchester, replacing existing track that is more than 30 years old. At Witham there are also track renewals and point replacements.
Overhead line renewals are being carried out at Chelmsford, while new points are being installed on the junction at Marks Tey for the Sudbury branch.
Network Rail Route Managing Director Richard Schofield said: “This investment is absolutely vital to help us deliver a better service for passengers. We know that people want to travel by train and not a bus, but the line from London Liverpool Street to Norwich carries a huge amount of traffic and desperately needs this boost
Buses will replace trains during the eight weekends.
NR said: “In 2015, there are currently no plans for any major disruptive engineering work on the main line out of Liverpool Street to Norwich beyond May to the end of the year that would require a bus replacement service during weekends on both days.”