Railway passengers are most at risk when boarding or alighting from trains at the platform-train interface (PTI) in stations.
Various methods have been used in the past to try to solve this but all fail in one way or another. Fixed-position mirrors or CCTV monitors on the platform are only useable while the train is at a standstill; as soon as it starts to depart, they cannot be viewed yet the risks remain. A guard can observe the departure from an open window on the train but platform curvature and other line of sight issues limit the effectiveness; in many cases other operational requirements prevent guards from being utilised anyway. Platform guards can be used but their duties are often interrupted by passengers and they still have to communicate with the train driver which may take critical seconds. Train-mounted cameras have been used before but often have distorted or relatively poor optics and sub-optimal placement driven by requirements and constraints of fitting within the limited loading gauge of the train. Some stations use platform-edge doors that do mitigate some issues, but also introduce many others such as passengers being stuck between platform doors and train doors or bag straps or dog leads getting caught leading to dragging injuries, so platform video monitoring is still required.
Our solution: Track to train CCTV transmission
To reduce the risk of death or injury our transmission solution gives train drivers complete visibility of the entire platform in order that they can react instantly to any safety issues. We use microwave transmission in licensed frequency bands to give guaranteed interference-free broadcast-quality video transmission with zero latency even underground. Live video from the optimally placed, high-quality platform cameras is combined and transmitted to the driver’s cab where the in-cab CCTV monitor displays bright and clear real-time images of the platform. This system reduces the response time to an absolute minimum and transmits continually until the entire train has departed the station.
Key benefits
Over 20 years service
Several variants are in service on railways across the world. A large number of systems are installed throughout the Mass Transit Railway (MTR) network in Hong Kong. Despite the MTR being generally regarded as one of the most demanding railway companies in the world, we have been supplying equipment to them for more than 20 years. We currently have significant orders for an extension to their network into mainland China. Our newest customer, the Ho Chi Minh City Metro now use our solution on their first metro line, which opened in December 2024.
High performance in challenging situations
We have supplied systems for several lines on the London Underground network. Our equipment operates at 105 London stations and on all 192 of the S-stock trains. These particular systems are specially adapted to overcome the difficulties associated with the age of some of the lines, which date back to 1863 and have unusual challenges compared to modern railways.
The technology
The system uses microwave transmission from discrete trackside transmitters to receivers on the train and employs a number of frequencies to avoid interference from transmitters on nearby tracks. Beacons tell the train which frequencies to tune to. Underground tunnels are difficult environments for microwave and radio transmission, so we use a sophisticated spatial diversity system where the receiver automatically selects the best quality video for display. The drivers always see a rock-solid picture when in fact it is rapidly switching many times as the train leaves the platform.
High reliability
All the equipment has an in-service reliability many times better than the specification and considerably better than Mean Time Between Failures (MTBF) predicted from a parts count analysis. The modular construction and Built In Self Test (BIST) circuits allow simple module replacement to occur in the depot if a fault does occur, minimising downtime. The robust and compact metal enclosures provide mechanical protection of trackside equipment. Microwave transmission avoids the use of long lengths of delicate leaky feeder cables that are vulnerable to damage.
Analogue or digital options
The equipment uses analogue video signals because there is no latency in the transmission. This is the preferred solution where the transmission ranges are relatively short, less than 100 metres or so, but if longer ranges are required or if there is considerable curvature in the track, then digital transmission using COFDM, similar to that employed in DVB-T terrestrial television broadcast, might be preferrable, although it may have a latency of up to a quarter of a second (250 milliseconds).
Multiple transmitters
An alternative for long or curved platforms is to use multiple transmitters over different lengths of the coverage with the receivers switching from one transmitter to another as the train progresses down the track. This is the concept used in for the London Underground system, but equally, we have proven the digital transmission concept, should it be required. For reference, a thorough comparison between all the different transmission concepts, including optical and leaky feeders, is available.