What is a pantograph and why does the MBTA Green Line use them?

A pantograph is the flexible, angled arm on the top of the trolley that connects the train to overhead power lines.

What's the deal with the pantographs? : r/mbta

MBTA AnsaldoBreda Type 8 - Wikipedia

Power issue halts Green Line service day after track defects revealed - CBS Boston

Full rail service resumes after 'pantograph issue' forced switch to shuttle buses for portion of Green Line's C Branch - Boston News, Weather, Sports

Boston: Subways, Wonderland, Trams and Mattapan

Another pantograph problem on the Green Line prompts delays, shuttle bus services – Boston 25 News

MBTA Blue Line

Passengers walk along tracks after MBTA Green Line extension shuts down

MBTA board approves $811-million purchase of Green Line 'supercars

MBTA Green Line