The Purple Line Extension Project spans a total of 14 kilometers (9.1 miles) and passes through Wilshire Boulevard, one of the busiest streets in Los Angeles.
The project was already equipped with sensors for monitoring various parameters such as pore water pressure, subsidence above tunnels, ground movements in-depth, horizontal displacements in-depth, induced movements in buildings (settlements and tilt), stresses in structural elements, stresses in tunnel linings and others. Some of these sensors were placed in boreholes drilled from the road surface or sidewalk. The project developers wanted to avoid interrupting traffic every time a sensor needed to be checked, but the alternative of installing cables to power and read the sensors, was too expensive because it would have required digging trenches for the cables. This made wireless monitoring the best solution.