Final answer:
The major innovation attempted at South Station was the implementation of an underground trolley system. The crowded streets made above-ground trolleys impractical and dangerous due to accidents, leading to the adoption of elevated trains and subways as a solution for urban transport.
Step-by-step explanation:
The major innovation that was tried at South Station but ultimately failed was the creation of an underground trolley system to avoid the congestion of street-level trolleys.
In many populous cities like New York, trolleys, which were significantly more efficient than horse-drawn carriages, often resulted in frequent accidents due to overcrowding on the streets.
To alleviate this problem, city planners began to move the trolley lines to elevated trains or underground as subways, similar to Boston's subway system which began operating in 1897 as the oldest subway tunnel in the United States.
Despite the innovation of underground trolleys at South Station, the concept faced challenges. The problem was exacerbated by the fact that trolleys were unable to move efficiently through the crowds of pedestrians.
This highlighted the need for a more sustainable solution, which eventually led to subways becoming a preferred method of public transportation in dense urban environments.