SubWave uses leaky coax cables to extend the reach of GPS positioning to underground infrastructure. The technology, which is already in use on the Stockholm metro network, enables accurate location of trains and other assets in tunnels. Syntony says SubWave can already be used for non-safety-critical applications but it expects to gain SIL 2 certification for the technology this year and aims to achieve SIL 3 and SIL 4 certification within two years. The trial deployment in New York will cover around 1km of tunnel.