The Elizabeth line has been up and running since May and there are already plans being outlined to extend it.
But plans proposed by Thurrock Council suggest it could go even further into Essex and Kent.
The council is attempting to put forward the idea of a 30-mile loop which would go through parts of both counties.
The idea is part of a wider proposal from Thurrock to improve local transport links.
Other plans include the possibility of adding connections to Fenchurch Street and Liverpool Street stations.
A map illustrating the plans shows the route would extend the London Overground line from Romford to Upminster.
It would then replace the existing single-track railway that runs between Upminster and Grays, onto Tilbury.
Finally, the line would go under the Thames out to the coast, in Gravesend, where it would link in with previously proposed extension between Abbey Wood and Northfleet.
However, there could be engineering problems to get around, as well as cost issues.
For example, a large flyover would be needed to link trains between Upminster and Romford as trains arrive at different sides of the station.
The plans are just ‘framework’ at the moment, but the council says: ‘[This would be] a transformation of Thurrock’s railways to support the delivery of new homes and jobs, improve public transport accessibility and realise the borough’s full potential as an important economic hub at the heart of the Thames Estuary.’
The council adds that its vision is to ‘realise the full potential’ of existing lines in the short to medium-term, while adding capacity through new rail lines would be a long-term project.
Elsewhere, the Abbey Wood to Northfleet extension is already estimated to cost around £3billion.
None of the issues surrounding cost and engineering work needed are highlighted in the report from Thurrock council.
But it does highlight that it would likely be more straightforward to upgrade the existing C2C line into London.
The proposal comes after data released last month shows that almost half of Londoners have already travelled on the Elizabeth Line.
Users who said they took a special trip to try it out has fallen from 37% in July 2022 to 25% in January 2023.
This suggests the route has already become part of people’s daily lives, with more than 100 million total journeys taken.
Metro.co.uk has contacted Thurrock council for comment.
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