I want to know the answer to the following question:
What was the transportation advancement made possible by Sprague's designs?
All the background I'm provided with is that "This allowed Sprague to use electric motors to invent the first electric trolley system in 1887–88 in Richmond VA, the electric elevator and control system in 1892, and the electric subway with independently powered centrally controlled cars, which were first installed in 1892 in Chicago by the South Side Elevated Railway where it became popularly known as the "L".". Is that enough to answer the question?
Answer: yes