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.
Original patent title: “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. Granted to Individual in 1923 with 2 forward citations, and it is now in the public domain.
Key facts
Coverage
What does this patent actually cover?
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.
The gap
What does this patent NOT 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.
These exclusions are unique to PatentBrief — derived from the actual claim language, not patent-office boilerplate.
What made this novel
The innovation was the introduction of a 'neutral' or 'caution' state that stopped all traffic flow, rather than just switching between two opposing directions.
The Patent Drawing
Schematic visualization of the patent's claim structure. Hand-drawn diagrams in progress for each landmark patent.
Where you've seen this
Real-world examples
Early 20th-century manual traffic control towers
Mechanical semaphore-style intersection signals
Why it matters
The bigger picture
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.
Filed
February 27, 1922
Granted
November 20, 1923
Market context
Who's building on this
Companies in this space
Modern traffic management companies like Econolite and Siemens build on the logic of intersection safety intervals, though they now use advanced AI and sensor-based systems instead of mechanical poles.
Market impact
This patent helped standardize intersection safety protocols in the early automotive era. It served as a critical bridge between unregulated, chaotic street crossings and the sophisticated, automated traffic management systems used in cities today.
Claim 1 — Plain English
What this patent 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.
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.
What it does not 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.
Patent Journey
From filing to expiry
PatentBrief Score
Impact Score
Limited data
Citation count
10/40
Early citations
Claim breadth
0/20
Narrow claimsclaimsThe numbered statements at the end of a patent that legally define what the inventor owns.Read more →
Recency
0/20
Older than 20 years
Assignee scale
0/20
Independent or smaller assigneeassigneeThe entity that owns the patent — usually the inventor's employer or a company.Read more →
PatentBrief Impact Score — based on citation count, claim breadth, recency, and assignee scale. Not a legal assessment.
Heuristic Value Estimate
What this patent might be worth
$5K – $14K
Midpoint $9K · expired or expiring · industry ×1.5
Heuristic only — blends forward/backward citation counts, claim scope, time remaining, litigation history, and CPC-derived industry baseline. Real valuations need a professional appraisal.
Concepts involved
Citations
Patent lineage
Cite this patent
Morgan, G. A. (1923). How Garrett Morgan Invented the Three-Position Traffic Signal (U.S. Patent No. 1,475,024). U.S. Patent and Trademark Office. https://patentbrief.org/patent/us/1475024/traffic-signal-morgan
Auto-generated from the patent record. Double-check author order and the issue date against the official USPTO document before submitting.
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Common Questions
Frequently Asked Questions
What does How Garrett Morgan Invented the Three-Position Traffic Signal cover?
Garrett Morgan's 1923 patent for a T-shaped traffic signal introduced a 'caution' position to manage vehicle flow more safely at busy intersections.
Who owns patent US 1475024?
Individual owns this patent, granted in 1923.
When does this patent expire?
This patent has expired and is now in the public domain — anyone can use the invention freely.
What is patent US 1475024 cited by?
This patent has been cited by 2 later patents that build on its ideas.
What problem does this patent solve?
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.
What does this patent NOT cover?
Does not cover electric or automated traffic light systems.
Same assignee
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