Why do traffic lights use red for stop?

Answer: Red light travels farthest distance

Red is easiest color to produce — Wrong. Red isn't easier to produce than other colors. Red was chosen because red light has the longest wavelength and travels farthest through fog/dust.

Red light travels farthest distance ✓ — Correct! Red light has the longest wavelength in the visible spectrum (~700nm). Long wavelengths scatter less in fog, rain, and dust, so red signals remain visible from farther away than other colors. This makes red ideal for the critical 'stop' command.

Most people can see red best — Wrong. Color perception varies, and red-green colorblindness is common. Red was chosen for its physical property—long wavelength makes it visible from far distances.