Network Rail has been urged by two councils to start improving the Norwich to London line.
Norfolk and Suffolk county councils have also written to the Transport Secretary Ruth Kelly about recent disruption to services.
The councils are calling for work to modernise the overhead power lines, some of which date back to the 1940s, to be speeded up.
Network Rail was unavailable to comment on the letter the councils have sent.
Adrian Gunson, from Norfolk County Council and the chairman of the Norfolk Rail Alliance, said there was growing concern that the age and condition of overhead lines near Chelmsford were putting reliability at risk.
'Rail disruption'
"We fear that the sort of disruption experienced recently... is damaging to the Norfolk and Suffolk economies."
Councillor Guy McGregor of Suffolk County Council added: "Rail disruption will only deter people from using trains to get in and out of the county."
Overhead lines are due to be replaced by 2012 but the councils want the work completed earlier.
In the letter, also sent to Ms Kelly, the councils have called for work on signalling to be brought forward, more upgrading of cross-country routes and high maintenance standards.
The two county councils have agreed to ask all their MPs for support over the issue.
As well as recent overhead line problems, a goods train derailed causing delays in June.
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