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The Random Fact Generator website told me:

By 1955, forty-nine of the U.S. states agreed that state highways should have a white stripe down the middle between cars going in different directions. The lone holdout was Oregon, who believed that a yellow line was safer. Sixteen years later, the government mandated these white lanes be painted yellow, proving Oregon right.

Is using yellow for a center line marking safer than white?

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    "Is it true that yellow is safer that white road marking" This isn't what's being said. Both yellow and white lines are found on roads in the US. Both are even used in the middle of the road. It's just that using a color other than white to separate opposing traffic means that you can tell the difference between a 1-way and a 2-way street just by looking at the pavement. Glass beads are not mentioned in the quote so I'm not sure why you bring them up.
    – Laurel
    Mar 26 at 13:25
  • The spherules of glass is because, 1955 the visibility technology isn't as advanced as today, and all road paint now has glass paint, that's why it glitters, it reflects the light of the cars at night. So, the statement sounds like it would not be an accurate generalization in 2022. The statement specifically talks abotut yellow being safer, which is very vague and I don't know why they'd state that.
    – bandybabboon
    Mar 26 at 13:31
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    @bandybabboon: Because no-one cited claimed that glass bead paint is safer or less safe, it isn't a notable claim here. I have focussed on the actual claim. [The notablility here is still dubious.]
    – Oddthinking ♦
    Mar 26 at 13:34
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    Also what doesn't make sense is that the government endorsement proves someone is right. Science proves theories, not government mandates.
    – bandybabboon
    Mar 27 at 5:25
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    The whole issue could be one of confusion between standardisation of markings being safer and yellow markings being safer. I can see why a national standard is better than variation (but the colour is arbitrary). But evidence that one colour is safer would need to explain why other countries didn't adopt the same standard.
    – matt_black
    Mar 28 at 15:02

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There are problems with that story

To start with a technicality, Alaska and Hawaii did not become states until 1959, so all-states-but-one would have been 47 states in 1955.

Yellow lines were already supposed to be used in certain circumstances in 1961. In 1961 edition of the Manual on Uniform Traffic Control Devices, part two:

2B-2 Center Lines on Rural Roads

The center line on a two-lane paved rural highway shall be a broken white line, [...]

On four-lane undivided rural pavements, or on pavements of a greater even number of lanes, the center line shall consist of two solid yellow lines [...]

2B-3 Center Lines on Urban Streets

The center line on a two-way city street with less than four lanes for moving traffic at any time shall be a solid white line. [...]

The center line on a two-way street with four or more lanes for moving traffic at all times shall be a double solid yellow line except on a street involving reversible lane control.

2B-8 No-Passing Zone Markings

A no-passing zone shall be marked by a solid barrier line placed as the right-hand element of a combination line along the center or lane line. This barrier line shall be yellow.

As these quotes show, there were times when yellow lines were to be used and times when white lines were to be used.

One thing that the story does get right is the change in 1971. The 1971 manual's part three has the following:

3A-5 General Principles-Longitudinal Pavement Markings

Longitudinal pavement markings shall conform to the following basic concepts:

  1. Yellow lines delineate the separation of traffic flows in opposing directions or mark the left boundary of the travel path at locations of particular hazard.
  2. White lines delineate the separation of traffic flows in the same direction.

So here we see that yellow lines did indeed become the standard divider between opposing directions at that time.

There has been at least one study about switching to all white lane lines. Among the reasons for possibly switching they list

  • All other factors being equal, white markings have higher retroreflectivity than yellow markings.
  • Most of the industrialized countries of the world use all-white pavement markings.

The study advises against switching because of the cost of implementing a switch and because drivers are already used to yellow lines. For safety, they say

Safety is a factor in any potential improvement to the transportation system. At this time, it is not possible to assess the possible reductions (or increases) in crashes that would be associated with implementing an all-white pavement marking system.

Looking at a chart of fatalities, there's no obvious change in the early 70's when yellow dividing lines became the standard. Do note that this is only fatalities, which would not show any effects on accidents in which fatalities were unlikely to occur.

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    My opinion (which is why I didn't include this in the answer) is that mandating the yellow lines was just to simplify things. Unfortunately I couldn't find any good references for their motivation. Also, comparing the 1961 and 1971 manuals made me feel like there was also a shift in intent, as if previously there was a greater expectation that people should be able to use the opposite lane for passing in most circumstances, while later they're effectively saying "no, people really shouldn't do that in most cases."
    – Rob Watts
    Mar 29 at 21:56
  • When I've been in white-line countries, I often found it somewhat terrifying (as a passenger) that it was seldom obvious where the traffic direction changes. If I were to drive there, I suspect I'd occasionally end up on the wrong side. ¶ Meanwhile, back at home, I find it so convenient and comforting at entrance ramps, shopping mall entrances, one way streets, etc. to see a yellow post or marker on my left. If I ever see yellow on my right, I'll immediately know I've made a bad turn and correct it at once.
    – Ray Butterworth
    Mar 29 at 23:13
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    @RayButterworth that's anecdotal evidence that changing systems could easily cause problems, but not that the other system is worse or better for those who are already used to it. I am definitely glad that the US has a standard so that it's consistent across states.
    – Rob Watts
    Mar 29 at 23:34
  • "changing systems could easily cause problems". But it's not symmetric. If my yellow lines suddenly became white, I might easily cross them; if other people's white lines suddenly became yellow, they might be a bit confused for a while, but it wouldn't alter their driving. ¶ "a standard so that it's consistent". Definitely. It's nice to finally see the inconsistent flashing-green-light going away. I once nearly turned left in front of oncoming traffic because in British Columbia it meant something completely different from what it meant in Ontario.
    – Ray Butterworth
    Mar 30 at 1:57
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    To you point that most other industrialized countries use all white: Germany uses white everywhere as the standard permanent markings and uses yellow for temporary changes of the road marking usually due to a construction site. So you will see white and yellow road markings on top of each other which means the yellow markings overrule the white ones and as long as the yellow ones are there the white ones are void.
    – quarague
    Mar 30 at 8:50

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