How Garrett Morgan Invented the Three-Position Traffic Signal

Garrett Morgan's 1923 patent for a T-shaped traffic signal introduced a 'caution' position to manage vehicle flow more safely at busy intersections.

What it covers

The patent describes a T-shaped pole featuring three distinct positions to control traffic flow. Unlike earlier two-position signals that only signaled 'stop' or 'go', this design introduced a third state to halt traffic from all directions simultaneously. This allowed for a safer transition period, preventing collisions between vehicles clearing the intersection and those just starting to move.

What it doesn't cover

• —Does not cover electric or automated traffic light systems.
• —Does not cover signals that use colored lights (red, yellow, green) as the primary indicator.
• —Does not cover systems that detect vehicle presence via sensors or loops.

The clever bit

The innovation was the introduction of a 'neutral' or 'caution' state that stopped all traffic flow, rather than just switching between two opposing directions.

Why it matters

Before this invention, intersections were dangerous places with primitive, two-state signals that often led to accidents. Morgan's inclusion of a 'stop-all' position provided the necessary buffer time for city streets, forming the conceptual foundation for the modern yellow light interval used worldwide today.

Real-world examples

• 1.Early 20th-century manual traffic control towers
• 2.Mechanical semaphore-style intersection signals