The automobile street signal colors of red and green were adopted because those colors were already in use by the railroads. Was the color red associated with "stop" before railroads? Was it ever associated with "Danger"?

Edit: The association with blood has always seemed like a backwards rationalization to me; we don't see a lady in a red dress, or watch the Chiefs play, and think "Blood! Danger!". But yes, I should have phrased it better, to ask about pre-stoplight associations. I probably didn't google with the right terms, but I seemed to run into sites that said things like "Red is the color of extremes. It’s the color of passionate love, seduction, violence, danger, anger, and adventure. Our prehistoric ancestors saw red as the color of fire and blood – energy and primal life forces – and most of red’s symbolism today arises from its powerful associations in the past.".

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    Quoting from the source you cite, "They chose red as the color for stop, it is thought, because red has for centuries been used to indicate danger." A simple google search reveals multiple additional answers example
    – MCW
    Commented Jun 17, 2019 at 17:34
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    @drewbenn: Ha ha! I always think of Blood! Danger! when i watch those Chiefs play. Commented Jun 17, 2019 at 21:40
  • we don't see a lady in a red dress, or watch the Chiefs play, and think "Blood! Danger!" How long has it been since the last time you hunted, skinned and cut into pieces your supper (Pizza does not count!)
    – SJuan76
    Commented Jun 17, 2019 at 22:08
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    @PieterGeerkens, hopefully recently and in the next 10 years! @Sjuan76...Apples? Commented Jun 18, 2019 at 12:41
  • there are physical reasons too... Yellow is obviously the sun's color, thus our eyes evolved to be more sensitive to yellow (which has more R than B or G - our eyes have Red, Green, and Blue cells). Red is also at the extreme of the visible spectrum, the energy threshold required to perceive red is lower to our eyes - so it is easier to see a red light in fog, e.g.. I think that at the end practical reasons would force any convention to converge to red / yellow / orange as warning colors, once people get used to practical difficult situations such as warning lights in rain or fog.
    – Luiz
    Commented Jun 19, 2019 at 13:23

1 Answer 1


Merriam-Webster dates the first usage of red flag meaning "a warning signal" to 1748, but it does not cite the example. However, the Collins Dictionary Trends of 'red flag' graph lends support to this early usage

Still well before railways, the earliest actual example of the use of red for a warning I've found is in this Wikipedia note:

1777 Philip Thicknesse, Year's Journey I. iii. 23 There is a red flag hoisted gradually higher and higher, as the water flows into the harbour [at Calais].

Early Western Travels 1748-1846 has this passage from 1812-1819, a possible reference to warning or danger:

Several times hearing the noise of cannon, and seeing a red flag hoisted, on inquiry I found that one or more negroes were to be executed.

The Army and Navy Chronicle, volume VI has this use (1837) of a red flag to warn against fog at sea:

In rainy and foggy weather, this vessel's bell will be rung for 10 minutes at a time, after intervals of 5 minutes duration. During the day time a red flag will be kept flying at the foretop, and in stormy weather a red jack will be hoisted at the same top.

Red did not actually become the standard warning colour on railways until 1841 or a little later, partly at the urging of Henry Booth of the Liverpool and Manchester Railway when his views were sought by the House of Lords Select Committee on Railways. The gas lamps sometimes used (with red or green glass) were soon phased out in favour of semaphore signals.

Perhaps the most notable use of red meaning 'warning' or 'danger' does, though, relate to railways (and other 'self-propelled vehicles') in the form of the The Locomotive Act 1865, also known as the Red Flag Act which stipulated that

self-propelled vehicles should be accompanied by a crew of three; if the vehicle was attached to two or more vehicles an additional person was to accompany the vehicles; a man with a red flag was to walk at least 60 yd (55 m) ahead of each vehicle, who was also required to assist with the passage of horses and carriages. The vehicle was required to stop at the signal of the flagbearer. (Section 3)

Red flags were also used by ships of the Royal Navy from at least 1602 to indicate that they were going to engage the enemy. A specific example is cited here in The Navy Chronicle. Also, pirates of the late 17th and early 18th centuries

actually bore no designs, but were flags of solid red or black. The origin of the red flag can be traced back to the English privateers of the late 1600s, who were required to fly red flags to distinguish their vessels from those of the Royal Navy. Many of these privateers later turned to piracy, and continued to use the red flag.

  • Are the early examples of "red flag" really purely red? Compare eg signal flag "Lima" called the "Yellow Jack" with "Quebec" & "Uniform"! (I guess your A goes in at a too-early date, even for locomotives… Commented Jun 18, 2019 at 9:28
  • @LangLangC Can't be 100% sure without contemporary visual or precise descriptive evidence, but one source I cited (Army and Navy Chronicle) does specify at one point 'red jack' in contrast to 'red flag'. Commented Jun 18, 2019 at 12:36
  • I think the "red Jack" is the flag the RN flies during war - Union Jack (Great Britain flag) in upper left corner, rest of flag is red. Commented Jun 18, 2019 at 12:39
  • @AmorphousBlob Since 1707, the Red Ensign has been used for merchant and passenger ships but it was also used by the Red Squadron of the Royal Navy until 1864. See Red Ensign for more info. Interestingly, the Red Squadron used a solid red flag in the 16th century. Commented Jun 18, 2019 at 12:53

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