A quick look at the Hammersmith Control Centre
Author: Patawee Jintana
Editor: Owen Harcombe
Disclaimer: this article was first published in the issue V of Guildsheet magazine on February 2020.
Imperial College Railway and Transport Society (ICRTS) was kindly granted a permission to visit Hammersmith Service Control Centre on December 12th, 2018.
Hammersmith Service Control Centre is the heart of the four lines modernisation (4LM) project aiming to increase capacity and improve journey experience across the 4 sub-surface underground lines (Circle, District, Hammersmith & City and Metropolitan) which make up of 40% of the London Underground network.
As you may be aware, the first phase of this project is in place with 192 air- conditioned, walk through trains now in service, replacing the older generation completely. The next steps in this project involve a lot of infrastructure work both inside the control centre, and out across the network.
After the warm welcome by staff, ICRTS were given an interesting lecture about 4LM and valuable experiences from operator pint of view.
Signalling systems — Out with the old, in with the new!
A signalling system is one of vital components of rail transport as it ensures passenger safety by preventing a train getting too close to the train in front whilst running at operational speed.
Trusty fix block signalling
Years ago, London underground and most metro systems relied on fix block signalling system. The principle of this system is simple. The railway is divided to many sections, where each section covers couple of hundred metres of track. A track-side signal protecting that block will only allow one train to enter the section at any given time. A train can be detected by applying a small voltage to the running rails. When a train is in the section, the wheels and axles close the circuit between the two rails, which allow electrical current to flow. This is detected by the signalling system which then sets the signal for the entrance to that block to red, stopping the next train from entering until the previous one has left. For safety reasons, at least one section will be reserved as a buffer to keep two running trains apart from each other.
The fix block system works, and many metro and mainline systems still use it, but there is one major problem. As the operator tries to run more trains to cope with increasing demand, the line capacity will be reached. If the demand exceeds the fix block system limit, a new signalling system must be deployed.
Communication Based Train Control CBTC: What is it? How does it impact your journey?
CBTC is a new signalling system that allows operator to squeeze more trains on existing tracks. It relies on continuous communication between each train and the control centre. With the aid of tags installed between the rails every 20–50 metres along the track, the control centre know exactly where trains are. Computers in the control centre can then give each train safe distance it can proceed, called a movement authority based upon where the other trains are on the track. On board computers installed on each train then calculate the appropriate running speed so that the train can come to rest before it collides with the train in front.
From the passenger point of view, this means more frequent train service with better live customer information. In addition, replacing ageing signalling system with a new one results in more reliable services and fewer signal failures. Once 4LM is fully completed in 2023, the capacity of sub-surface line will be increased by 33% during peak hours. Not only receiving more frequent services, passengers will eventually benefit from night tube on some parts of sub-surface lines as well.
What can be controlled from Hammersmith?
Basically, almost everything from monitoring the entire system to redirect a train to new destination. On the simulator, ICRTS was shown how staff in the control room can order a train to skip a station, hold a train at a station or between two stations, put a temporary speed limit on some sections or block all trains from entering some sections and reroute them instead.
Additionally, staff can monitor CCTV cameras installed on the platforms. They can see some people playing a popular commuter game called ‘Which Train Will Leave First’ at some stations such as Earl’s Court. ICRTS was told that seeing commuter moving back and forth trying to figure out which train will depart first is funny indeed.
Once the entire system is up, driving an underground train might be a bit more boring than it used to be. In fact, the system was designed to be capable of fully automatic operation without a driver in any circumstance. However, for public safety concerns, there will be a trained driver on board to deal with unexpected incident in foreseeable future.
Challenges of Installing 21st Century Signalling on Victorian Infrastructure
In most new metro systems, railway tracks dive over or under each other at junctions to allow train to pass through without affecting other trains coming from other direction. Unfortunately, Victorian engineers did not expect that the metro network they started would experience such a high demand in the 21st century. In those days, a train ran every 10–15 minutes with fewer passengers compared to today. As a result, features like flat junctions and short platforms at Baker Street station which were completely acceptable in Victorian era become bottlenecks of the modern system today.
As it is technically and financially impractical to close the lines and rebuild these junctions. The only choice remaining is to leave it to crack team of programmers to design the special software for London Underground. This software must deal with the four main flat junctions across the sub-surface underground network and schedule trains to prevent them from having to stop and wait for the junction to be cleared. Due to this complexity, not all railway signaling companies can handle this. Also, software needed to be checked and thoroughly tested to make sure that it will never cause an accident.
Shared Track
The other challenge for 4LM is the fact that some parts of sub-surface track are shared with national rail or other London Underground line. As trains operating on national rail network were designed to work with different signalling systems, computers in the control centre control track-side signal in the shared sections for both underground and other trains. For the shared section with other London Underground line, the railway signaling company that awarded the contract needed to make sure that the system will be compatible with the other line. The final solution to be put in place will be confirmed once the other line gets the signaling system upgraded.
Platform Edge Doors
In many new-built metro stations around the world, platform edge doors are important feature. (In London, underground stations in Jubilee Line extension and Elizabeth Line can give you an idea about what full-height platform edge doors look like.) The staff told ICRTS about the fact that the ‘main purpose’ of full-height platform edge doors is not all about preventing person or item from falling into railway track but to control the air flow in the tunnel.
Nowadays, many metro operators in major cities try to modernise their own network by installing platform edge doors. ICRTS was told that it is unlikely that installation platform edge doors on all existing stations will happen in the foreseeable future as many platforms across the London Underground are curvy (like curly fries). To make things even worse, some of them are S-shaped. These platforms were not designed for current day technology platform edge doors those require ‘almost straight’ platform to accommodate them.
The other limitation is the train fleet. With an exception of special designed platform edge doors, once platform edge doors are installed, that platform can only accommodate the train whose doors match the platform edge doors. This means for the lines that platform screen doors installation plan is in place, the current rolling stock must be replaced before they are fitted.
Safety Issues
Safety and security are important factor behind a lot of designs and decisions involving 4LM project. This is because London Underground is very important transport infrastructure that millions of people rely on. The system needs to be up and running almost 24/7. In the rare event the system must shut down unexpectedly, a rigid plan is in place to ensure the network can be evacuated quickly and safely. The control centre is designed to be able to remain online to coordinate the evacuation if one was required.
Being such a critical piece of infrastructure, the Hammersmith control centre is a highly secure building with several fences and physical obstacles to prevent unauthorised access. It has two different power supplies and back up generators to ensure it is never without power and can sustain its staff for a few days in the event it must be locked down because of a security incident.
CBTC highly rely on trains communicating over a special Wi-Fi network that is installed in the tunnels solely for this purpose. Although the technology is the same, unauthorized devices are not permitted to access it. In the event the computers do detect a foreign device attempting to masquerade as a train, the system will fail into a safe state by ordering all trains in the vicinity to stop and ignoring messages from the suspicious devices.
Did you know?
- Hammersmith depot had been used to maintain C-stock trains. After S7/S8 stock took over, it turned into a siding.
- The Four sub-surface lines are divided into 14 signaling areas.
About the Author
My name is Patawee Jintana. I am a final year Mechanical Engineering student at Imperial College London. I was a secretary of ICRTS in 2018/19 and 2019/20 academic years.
