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The Washington Metropolitan Area Transit Authority (WMATA) is expanding a pilot of a new waterproofing membrane along the Red Line.The agency will continue installing the material along another 4,000-foot section of inbound track between the Medical Center and Grosvenor stations. The material is injected into the tunnel walls to form a waterproof membrane on the exterior of tunnel walls. The work is aimed at mitigating leaks that could cause arcing insulator incidents.WMATA in summer began testing the material on a 2,000-foot section of inbound track on the Red Line. Tunnels in that segment have remained "relatively dry, even with excessive rains in late July and August," WMATA officials said in a press release.Those Red Line segments were built before widespread use of the "New Austrian Tunneling Method," which provides tunnels with a waterproof membrane. Injecting the material requires drilling hundreds of holes through the tunnel ceiling and can only be done when trains aren't running. As a result, WMATA will temporarily single-track Red Line trains on weeknights over a six-week period. The work also will require two weekend shutdowns.