His contributions were especially important in promoting urban development by increasing the size cities could reasonably attain (through better transportation) and by allowing greater concentration of business in commercial sections (through use of electric elevators in skyscrapers).

After he was transferred to the USS Lancaster, the flagship of the European Squadron, he installed the first electric call-bell system on a United States Navy ship.

Sprague took leave to attend the International Exposition of Electricity of 1881 in Paris and the Crystal Palace Exhibition in Sydenham, England, in 1882, where he was on the jury of awards for gas engines, dynamos and lamps.

By the summer of 1888, Henry M. Whitney of the West End Street Railway in Boston had witnessed the simultaneous startup of multiple streetcars on a single power source and had signed up for conversion.

[8]: 10  By January 1889, Boston had its first electric streetcars – which would be the first in the Americas to go underground, some eight years later, as the Tremont Street Subway[9] – and which had become so popular and noteworthy that poet Oliver Wendell Holmes composed a verse about the new trolley pole technology, and the sparking contact shoe at its apex:[8]: 10 Within a year, electric power had started to replace more costly horsecars in many cities.

[10] Sprague's system of electric supply was a great advantage in relation to the first bipolar U-tube overhead lines, in everyday use since 1883 on the Mödling and Hinterbrühl Tram.

While electrifying the streetcars of Richmond, the increased passenger capacity and speed gave Sprague the notion that similar results could be achieved in vertical transportation — electric elevators.

By means of relays energized by train-line wires, the engineer (or motorman) commands all of the traction motors in the train to act together.

Along with William J. Wilgus, he designed the Wilgus-Sprague bottom contact third rail system used by the railroads leading into Grand Central Terminal.

Then, in the 1920s, he devised a method for safely running two independent elevators, local and express, in a single shaft, to conserve floor space.

Sprague's inventions made modern light rail and rapid transit systems possible, which today still function on the same principles.

A five-horsepower Lundell electric motor used at the Cockatoo Island Dockyard between 1900 and 1980 is now in the collection of the National Museum of Australia in Canberra.

His interest in his work never ceased; only a few hours before the end, he asked to have a newly designed model of his latest invention brought to his bedside.

[19] Other papers, including six volumes of congratulatory letters and photographs presented to Sprague on the occasion of his 75th birthday, are held at the Chapin Library, Williams College.

At its peak, Sprague Electric employed 12,000 people worldwide with plants in Scotland, France, Italy, and Japan, in addition to multiple locations in the United States, to become a leading manufacturer of capacitors and other electronic components.

[22] In 2017, Sprague was the subject of an episode on season 29 of American Experience, a documentary series that was broadcast on PBS television stations.

Titled The Race Underground, it partly chronicled the beginnings of the Boston-area MBTA's streetcar network, and described Sprague as "The Forgotten Hero of the American Subway".