Have you ever heard of the Weed Killer train? Not many people have, yet it plays a vital role in the maintenance and smooth running of the UK’s railway infrastructure. Without this behind the scenes maintenance Britain’s railways would more than likely grind to a halt, and disrupt not just the every- day travel of commuters, but also the transportation of goods and services across the length and breadth of the country. In spite of the ever-spiralling growth of the motor vehicle, the railway network is still crucially important in Britain. There can, however, still be ‘natural’ problems, like sudden climatic changes, that have the potential to bring the network to a standstill. Yes we’ve all no doubt complained about delayed journeys caused by what we regard as limp excuses like leaves on the track or frozen points, but these are real problems for the network, and real problems demand real solutions. So how do train companies face up to these problems? How does Railtrack manage to keep the network functioning when nature doesn’t do what it’s told?
Most people would suspect that the answer would be simple: use weed killer or de-icer and the problem will be sorted. Unfortunately it isn’t that simple. We now live in an environmentally-conscious age, where such practices are simply not acceptable: we quite correctly demand that the application of any herbicide or chemical compound solution has to be selective in order to protect the natural wildlife. So how do railway companies deal with the problems whilst ensuring they adequately protect wildlife? They use the latest Total Drop Control (TDC) spray applicators along with cutting-edge GPS technology.
However, although this solution is extremely effective, it I still not altogether totally risk-free. There are still other problems that they need to be addressed. The traditional methods of using a ‘weed killer train’ have worked effectively for a long time, but environmental concerns now mean that the companies have to exercise extreme caution when applying any chemical substance in the vicinity of the track and the surrounding areas. If they use too great a concentration of a chemical, the wildlife could suffer: certain weed killers have been scientifically proven to kill species like the lesser spotted newt, which is protected by law. On the other hand, using too weak a concentration of weed killer will simply mean that the problem will re-occur. The good news is that the train companies are now able to rely on new technology to ensure that they deliver the correct concentration of herbicide in an ecologically-approved way which effectively avoids any risk of point source pollution.
The technology works like this. The dispensing equipment is fixed to the train itself and is controlled by a GPS sensor: the flow of the chemical spray is linked to the speed of the train and is in turn monitored by a speed sensor. Unfortunately as good as GPS technology is, it too has its limitations. Britain’s railways have lots of tunnels and many trees which can affect the accuracy of the equipment. Therefore the train companies use Doppler radar technology to overcome this problem. Doppler non-contact radar speed sensors are already widely used by UK rolling stock engineers, and are valued for both their accuracy and their low cost. The new single beam and dual beam sensors provide accurate, independent speed and distance measurements in many railway environments. They are currently in use of both test tracks and the main lines. The latest application of Doppler radar technology has been refined to give accurate speed and distance data, free from the errors normally associated with wheel slip, GPS blank areas or surface changes. Because the non-contact radar Doppler speed sensor device is fitted independently from the train’s wheels, it is not affected by wheel slippage. These sensors also indicate the direction-of-travel, and offer both digital pulse and/or analogue voltage outputs.