Pepco is the city's electric utility and services 793,000 customers in the district and suburban Maryland. An 1889 law prohibits overhead wires within much of the historic City of Washington. As a result, all power lines and telecommunication cables are located underground in downtown Washington, and traffic signals are placed at the edge of the street. The D.C. Public Service Commission approved a seven-year, $500million plan in 2017 to bury more lines underground; construction started in 2019.