Installing sensors along a railway track to gather large quantities of real-time physical and technical data on train performance helps to improve the overall quality of the rail system and enhances safety.
Though we may dream of taking a ride in one of the magnetic levitation (Maglev) trains pioneered in Japan, floating over the track guided by magnets instead of travelling along on the old steel wheel and track system, a project being run by Hong Kong Polytechnic University offers some incremental improvements that may perhaps be more economically viable and more efficient. Over the last seven years, a remarkable experiment has been taking place along the 36 kilometres of track which connects Hong Kong with mainland China. Fibre optic sensors have been placed at regular intervals along the track, to measure and detect potential problems and gather a host of different types of information arising from the repeated passage of the trains. Sensors are also embedded in the mechanical parts of the trains. Under this Hong Kong initiative – a highly practical example of the machine-to-machine approach to smart objects – attention is focused on the contact between track and train, opening up a range of potential improvements to rail travel, the safety aspect being of paramount importance.
The new sensor system is based on a technology developed in the 1970s and 80s known as a Fiber Bragg grating (FBG), a type of sensor that reflects narrow spectra of light whose wavelengths shift due to temperature and/or strain variation. Coupling FBGs with a mechanical transducer – a device which transforms one type of signal into another, for example a light signal into an electrical signal – allows pressure, acceleration and other parameters to be measured. Thus both the train driver and the station operator on the platform who is monitoring the data can be alerted to an accident in the making. For instance, when excessive vibrations indicate that a train might be too heavy, the driver can be notified so that s/he can make any necessary adjustments, first and foremost by reducing train speed. The Hong Kong researchers are trying to provide train drivers with a comprehensive range of data and immediate alerts where necessary so as to avoid potential accidents. The system relies exclusively on optical detection and communication, so there are no problems with electromagnetic interference from electronic devices in use or from the power lines that run alongside many modern railway lines.
New safety standards in line with the expansion of high-speed trains
In comparison to air transport, railways are relatively cheap to run and quite easy to build, but everything still depends on ensuring the right relationship between train and track. If a train is travelling too fast, if it is too heavy or the rails are in a poor state, there is a very real risk that the train will derail. This was the background to the Hong Kong Polytechnic University project: the researchers were looking for a simple, low-cost way to improve safety. The experimental system has proved itself viable, and now Australia and Singapore are planning to roll out the system on their railways. The optical surveillance system costs less than a third the price of other warning systems, and saves the Hong Kong rail company an estimated $250,000 every year in maintenance costs. With high-speed rail in China now undergoing a major development boom, using the optical monitoring system throughout the country could make a major low-cost contribution to railway safety there, or anywhere else in the world.