Asked by: Nigel Wight, Exeter
To keep 1,000-tonne, 150m long Tunnel Boring Machines (TBMs) like those used for London’s Crossrail project on track, engineers rely on a laser-based system. Precise reference points are set up below ground behind the TBM, and laser beams are sent out from them into receivers in the machine. This keeps the TBMs heading in the right direction to within a millimetre or so over distances of up to 100 metres.
Robert is a science writer and visiting professor of science at Aston University.