 Built to replace the Charlestown Elevated and originally intended to be extended as far as Reading, it opened in stages between 1975 and 1977.Unlike the Washington Street Elevated (which was built as the same time and with a similar design), the Charlestown El was located very near Boston Harbor and the Mystic River tidal estuary, and was thus continually exposed to accelerated corrosion caused by salt air.The elevated was also unpopular with many local residents, as it was noisy and blocked out sunlight to Main Street.