William Phelps Eno was an American businessman responsible for many of the earliest innovations in road safety and traffic control. He is sometimes known as the "Father of traffic safety", despite never having learned to drive a car himself.

Aquilo was a steam yacht which was built in Boston in 1901 for William Phelps Eno, a wealthy man who was the inventor of the stop sign. In 1910, Eno sold Aquilo and the yacht was brought to the west coast of North America, where it was operated principally in Puget Sound and coastal British Columbia. Aquilo had a long succession of wealthy owners. In 1966, the yacht caught fire and sank while en route from Seattle to Los Angeles.