Crossrail 2 Swirl is a plan to take Crossrail 2 via Earlsfield, not Balham. The big issue with Swirl is that it does not directly relieve the Northern Line. This article provides a way to achieve that - "Swirl-Max".
How can Swirl be enhanced to relieve the Northern Line?
The Swirl plan deliberately takes Crossrail 2 away from the Northern Line. This is because any shared station (Balham or Tooting Broadway) on the main Crossrail 2 line allows passengers from places as diverse as Chessington, Kingston, Shepperton and Epsom to change onto the Northern Line, as well as for passengers to change from the Northern to Crossrail 2. My research suggests that the movement from Crossrail 2 to Northern will not be insignificant, and as such, it is far from clear that Crossrail 2 will make the Northern line less overcrowded. See my full analysis.
It is the case that simply by being built, Crossrail 2 will attract some journeys away from the Northern. This will notably be the case for residents around South Wimbledon. However, it is accepted that the Swirl plan alone would make little difference to Northern Line crowding.
Initially, it seemed that the best way to relieve the Northern Line would be to extend the Northern Line (West End Branch) from Battersea Power to Clapham South and/or Balham. However, the journey time analysis showed that such an approach would not achieve its goals, at least in part because the Northern Line Extension to Battersea Power does not interchange with the Victoria Line. As such, my view is that the best option is a branch of Crossrail 2 to relieve the Northern Line.
Swirl-Max - relieving the Northern Line
The Swirl-Max plan is an extension of the Swirl plan, proposing a branch of Crossrail 2 to relieve the Northern Line.
The branch would split from the main Crossrail 2 route south of Clapham Junction. It would then proceed to Balham, using a station alignment next to the existing station (the road between the station and Sainsburys). From there, it is proposed to take the branch on to Streatham.
Once the branch reaches Streatham, it makes sense to bring it to the surface to take over the existing line (coloured orange on the map) through Tooting (mainline) and Haydons Road to Wimbledon, where the branch would terminate. An additional station would be provided on the A24 near Tooting St.Georges hospital. The key benefit of doing this is that both Balham and Tooting on the Northern Line are relieved - it is no longer a choice of one or the other.
Note that all services from Chessington, Epsom, Kingston and Hampton Court would run via Earlsfield. The layout of the tracks at Wimbledon would make it impossible for those services to run via Streatham.
The branch would have 10tph (trains per hour), one every 6 minutes. While it may seem slightly low, this frequency does not turn out to be a problem for the branch. While relatively few people will change from the Northern Line to Crossrail 2 at Balham, my journey time analysis suggests that the numbers who would change with TfL's scheme are not as great as might be imagined. Thus, the key to relieving the Northern Line is attracting enough people to start their journey on Crossrail 2, rather than on the Northern. The Swirl-Max plan does this by providing four stations near the Northern Line - Balham, Tooting, St.Georges and Haydons Road. All four would provide competitive journey times to the West End, and considerably more comfort.
It is proposed that the 10tph currently proposed to terminate at Wimbledon would run via the Streatham branch. The key purpose of the 10tph TfL want to terminate at Wimbledon is to provide performance management for the core Central London section of Crossrail 2. As such, it is vital that the branch be able to perform the same role.
To ensure reliable performance, the branch would need to have two specific characteristics. Firstly, the branch must be completely isolated from Network Rail. Secondly, the branch must have overhead electrification (to avoid any problems due to changing from overhead to third rail power supply). When considering possible branches, these two characteristics were key.
The proposed branch is in tunnel from Clapham Junction to Streatham. South of Streatham, the branch would surface and completely take over the line from Streatham to Wimbledon, without sharing any track between Streatham and the junction for Tooting. The existing Thameslink services on that line would be diverted to run via Sutton to Wimbledon, effectively doubling the service between Sutton and Wimbledon.
The Tooting Broadway station saga has indicated that there is some tricky geology in the area. To mitigate this, it is proposed to build top-down station boxes at both Balham and Streatham. This should keep the stations within the band of London Clay.
At Wimbledon, it is proposed that platform 10 would be used for the Thameslink service from Sutton, and platform 9 for the Swirl-Max Crossrail 2 branch service via Streatham. Terminating 10tph in a single platform is not desirable, however it is feasible. It should be possible to provide an additional platform 11 in the area of the Queens Road car park to mitigate this. There is the potential to extend platform 10 south under the existing deck to provide more space. Furthermore, it is expected that an additional turn-back location would be provided somewhere along the branch. It is intended that at least a single track would be provided between platform 10 and the Weir Road depot for empty stock movements.
The proposed tunnel portal site is at, or near, Wandsworth Prison. While it is not yet certain that the prison will be closed, it must be considered at least possible. That site has reasonable road access via the A214, however it is assumed that most spoil would be sent down the main running tunnel to the New Malden portal. As such, tunnelling for the branch would begin later than that for the main line. If the prison does not close, the nearby car parks and nursery offer sufficient space for the worksite.
If the prison site does become available, it may be possible to move the "tunnel swap" location of the Swirl plan to the north of Earlsfield, near the prison. Doing so could save £300m by avoiding the need for a new sub-surface Earlsfield station.
While not essential, it is considered desirable to provide at least passive provision for four platforms at Clapham Junction. Doing so, could allow the branch to be separated from Crossrail 2 at some future point in time.
When deciding on the plan above, some other options were rejected. A one station branch to Balham or a two station branch to Balham and Streatham Hill would not attract enough traffic off the Northern Line. A route via Streatham Hill to Streatham would add to journey time and costs, plus be complicated to build (no easy way to create a tunnelled station at Streatham Hill. A branch with a tunnelled station at Tooting Broadway would run into the same geological problems that caused TfL to move to Balham.
The Swirl-Max plan has the same benefits as the Swirl plan, plus these additional benefits:
- Northern Line relief at both Balham and Tooting
- Ability to provide a station on the doorstep of St.Georges hospital
- No risk of overloading the Northern Line with passengers from beyond Wimbledon
- Significantly faster and more frequent service to Streatham
- Doubles the Thameslink service between Streatham and Sutton, and Sutton and Wimbledon
See also the full journey time analysis. For example, Streatham to Tottenham Court Road on Oxford Street would take just 15 minutes, with a train every 6 minutes.
It is difficult to quantify the potential Northern Line relief. However, if the four stations Haydons Road, St.Georges, Tooting and Balham could capture 35% of the traffic from the Northern Line at Colliers Wood, Tooting Broadway and Balham then around 1 in 4 people would be removed from the Northern Line north of Balham.
In addition, Swirl-Max provides far greater Victoria Line relief than the TfL scheme. This occurs, because many people that currently take the bus from Streathan to Brixton would instead take Crossrail 2 at Streatham.
My calculations suggest that this plan does not require a shaft on Wandsworth Common. This is because the proposed route is more direct to Balham. As such, a shaft at the prison site would suffice between Clapham Junction and Balham.
The following is a rough cost estimate for the Swirl-Max plan:
- Balham station - £300m
- Streatham station - £300m
- Additional tunnelling - £600m
- Surface works to take over line via Haydons Road - £300m
- Additional items / contingency - £500m
This comes to a total of £2bn. But it is important to remember that this is a high level estimate.
Potentially this means that the Swirl-Max plan is more expensive than TfL's current plan taking Crossrail 2 via Balham. However, it seems reasonable to suggest that Swirl-Max provides better transport benefits and greater reach for economic growth. A formal economic analysis would be needed to confirm this however.
While it is possible to end the branch at Streatham, it would seem that doing so misses the potential Northern Line relief from the Tooting and St.Georges stations. The additional cost to reach Wimbledon from Streatham should be easy to offset against the additional benefits.
The Swirl-Max plan for Crossrail 2 extends the Swirl plan, providing a branch from Clapham Junction to Balham, Streatham and Tooting. Instead of the question being "Balham or Tooting", it can be "Balham and Tooting, oh and Earlsfield and Streatham too!".
Feel free to comment to ask questions or support the plan.