The Purple Line Rail Link in Washington D.C. is a 16.2 mi (26.1 km) light rail line under construction to link the Maryland suburbs to the Washington metropolitan area. The line will allow riders to move between the other lines of the Washington Metro transportation system without needing to ride into central Washington, D.C. Meanwhile, the Purple Line Extension in Los Angeles, formerly known as the Westside Subway Extension and the Subway to the Sea, is a new heavy rail subway corridor in Los Angeles County, extending the Metro Purple Line from its current terminus at Wilshire/Western station in Los Angeles to the Westside region.
The two projects had similar pain points. While installing cables, some of the sensors were placed in boreholes drilled from the road surface or sidewalk. Installing cables to power and read the sensors were too expensive due to the necessity of trenches. The instrumentation monitoring in a tunnel is crucial not only during the initial phase of tunnel boring but also for some time after project completion. During the initial tunnel construction stages, it is very costly and inefficient to conduct monitoring using cabling because of the rapidly changing environment as the tunneling progresses, difficult access areas, etc. The sensors could be read manually but it required traffic interruptions and resulted in sporadic data acquisition. Also, the nodes are usually installed underneath manholes covered with a metal lid which is a very limiting condition for the radio transmission.