As the 20th century approached, Boston was choking on its own success - its streets were just too crowded. Today, the Green Line is a reminder of the innovation it took to deal with the problem - the nation's first subway and all, opened in 1897.
But putting trolleys, and eventually longer subway cars, underground wasn't the only way Boston tried to overcome its over-clogged streets. Dedicated mail streetcars and pneumatic tubes also played a key, if ultimately just short-term, role. Read more.