Philadelphia - Service supervisor John Stevens uses a two-way radio to tell has office that a Philadelphia Transportation Company trolley is cleared to continue its course. Forty two service supervisors are strategically located throughout the city where they are alerted by radio to check on tardy trolleys. The system is controlled from a centralized headquarter where a battery of time switched developed by GE engineers keep track of the progress of the trolleys.

General Electric Company1951-04-19