Metropolitan Line Southern Extension?

The Transport Secretary, Chris Grayling, recently killed off the plan to allow the London Mayor to take over the Network Rail lines in South East London. This was despite a high benefit:cost ratio and broad agreement between all groups concerned earlier in 2016.

Given this, and the difficulty more generally of providing enough capacity in south London, this blog considers an alternative plan to provide additional capacity for South East London.

Metropolitan Line Southern Extension

South East London has a reasonable network of rail lines, and they reach two good central London terminals at Cannon Street and Charing Cross. But the time is fast approaching when that network is simply beyond capacity. Rather than look at Crossrail 3, or other super-expensive solutions requiring a new tunnel across Central London, it is time to consider extending the Metropolitan Line. Such an approach would complement the proposed Bakerloo Line extension to Lewisham.

Having looked at the options, an extension to Abbey Wood seems to make the most sense. In this scenario, the Elizabeth line (Crossrail 1) would extend to Dartford (or beyond) using the existing tracks:

The full route would be as follows:

• Aldgate - rebuilt, interchange with District line
• City Hall - new underground station
• Bermondsey - underground interchange with Jubilee line
• Surrey Quays - underground interchange with Overground
• Deptford
• Greenwich - interchange with DLR
• Maze Hill
• Westcombe Park
• Charlton - interchange with service to Lewisham & Victoria
• Woolwich Dockyard
• Woolwich Arsenal - interchange with DLR
• Plumstead
• Abbey Wood - interchange with Elizabeth line (Crossrail 1)

For comparison, here is the existing map:

The first question to ask is whether it is possible to extend the Metropolitan Line at Aldgate, the current terminus.

Given this is a site at the edge of the City, it is certainly tricky, but it seems that it should be feasible. Just south of the existing Aldgate station is a large bus station (behind the buffer stops in the second picture). The extension would use the bus station site to develop the new interchange station using standard top-down construction. To provide space, the Metropolitan line and Hammersmith & City line trains would have to terminate at Liverpool Street during the works, with the Circle line ceasing to run. The goal of the construction would be to build a four platform station - two platforms for the District line above two platforms for the Metropolitan line.

The Metropolitan line trains would need to descend from the current level to be beneath the District line. This would be achieved using the site of the existing Aldgate station (the first picture). Once complete, the tracks would be covered over, and the station turned into a bus station. The site of the new station (the existing bus station) would be developed.

Once complete and open, the service patterns of the existing lines would change radically. There would be no Circle line and no Hammersmith & City line. District line trains would all run from Earls Court through Victoria and Tower Hill to Whitechapel. Similarly, Metropolitan line trains from Hammersmith and Harrow would all run through Liverpool Street and on to Greenwich and Abbey Wood. In the west, a shuttle service would run from Edgeware Road to Gloucester Road in place of the existing Circle line. This service pattern eliminates most of the flat junctions from the District and Metropolitan lines, making services much more reliable and able to run at a higher frequency. Note that the loss of services from Liverpool Street to Whitechapel (the current Hammersmith & City line) is mitigated by the Elizabeth line, which runs on exactly that route.

Constructing the rest of the proposed extension is relatively easy by comparison with Aldgate station. It would involve two tunnel boring machines and three underground stations. The station at City Hall would be entirely new. The station at Bermondsey would be an underground interchange, designed for ease of use, while the station at Surrey Quays would require a rebuild of the Overground station as well.

The Bermondsey interchange is key to the success of the plan, because it provides passengers from the extended Metropolitan line a simple change to reach the West End. Journeys such as Greenwich to Bond Street become a pleasure, with one simple well-designed interchange. This is vital, as it greatly increases the time benefits to passengers, boosting the business case.

The final piece of the puzzle will be a tunnel portal location to access Deptford. One possibility would be to use the land of the New Cross branch of the Overground. Such an approach would allow more Overground services to run to Clapham Junction, Crystal Palace and/or West Croydon, but would also require the Metropolitan extension to have a short branch to New Cross.

Costs and Benefits

The benefits of this scheme are not limited to the line through Greenwich, because the scheme would free up paths into Cannon Street. (No services would run from Greenwich to Cannon Street - the line through Greenwich would be transferred from Network Rail to TfL.) Currently, there are 7 trains per hour from Greenwich to Cannon Street between 7am and 9am. These paths would be reallocated to other services, benefiting passengers on other lines, including the routes to Sevenoaks, Hayes, Bexleyheath and Sidcup.

Passengers currently using services from Greenwich would still have direct trains to the City, but would have a choice of Aldgate, Liverpool Street and Moorgate instead of Cannon Street. Passengers for London Bridge would get off at City Hall, while passengers for the West End would change at Bermondsey. As such, existing passengers would not see major changes to their journeys causing disbenefits.

Costs are always hard to estimate, but a rough guess can be based on 5km of tunnelling, four underground stations and line conversion works on takeover from Network Rail. Say £500m for the tunnels, £1bn for Aldgate, £2bn shared between the other three underground stations, and £1.5bn of other work, suggests a possible total of £5bn. This compares with £3bn for the Bakerloo line extension, so the cost estimate seems sound enough.

The cost of extending the Elizabeth line to Dartford would need separate examination. I'd note that initially, the Metropolitan line extension could run to Charlton, rather than Abbey Wood to side-step that problem.

Summary

This is a proposal to extend the Metropolitan line from Aldgate to South East London, taking over the line from Deptford to Abbey Wood via Greenwich and Charlton. It provides a step change in service to that line, a radically simpler and more reliable service on the District line, and an additional 7 peak-hour paths into Cannon Street for the rest of South East London and Kent. And all for around £5bn.

Given that there won't be a TfL run South Eastern Overground any time soon, a plan like this may well be the best way to improve rail services in this part of London. Thoughts welcome!