What was a forerunner of the electronic controllers used in modern traffic systems?

The electronic controllers used in modern traffic systems evolved from earlier technologies that managed traffic flow. The electro-mechanical controller is identified as a significant forerunner because it integrated electrical components and mechanical functions to improve the control of traffic signals.

These controllers operated using a combination of relays and timers, allowing for more sophisticated traffic management compared to purely mechanical systems. They could be programmed to change lights based on time intervals or vehicle detection, which laid the groundwork for the development of fully electronic systems.

While timer-based, pneumatic, and hydraulic controllers also played roles in traffic management, they did not combine both electrical and mechanical components in the way that electro-mechanical controllers did. Timer-based controllers relied solely on set time intervals for signal changes, while pneumatic and hydraulic controllers used air pressure or fluid pressure, respectively, to operate mechanical signal devices. The advancement to electro-mechanical systems represents a critical step towards the sophisticated electronic controllers that manage traffic today.