3289: Highway Signs

Highway Signs

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Title text: Highway engineers like Planck units because, like the speed of light, the energy capacity of a typical car's gas tank is 1.

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Explanation

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In Planck units, speeds are measured in terms of the speed of light, c. 0.000000097c is ~104.6 k/h or 65mph.

The "Next Exit" sign references the Planck Length, which is the (theoretically) smallest possible length, equal to approximately 1.616255 × 10^-35 m. 1.39 × 10³⁹ Planck lengths is about 22.5 km, or 14.0 miles. It would likely be impractical for drivers to count the digits in that sign at highway speeds^{[Citation Needed]}. The signs would be better if they provided the numbers in scientific notation for those drivers who understood it, perhaps in addition to the displays as currently shown.

The title text claims that highway engineers like Planck units because the energy capacity of a gas tank is 1. It is true that the Planck Energy is approximately equal to the chemical energy stored in a typical gas tank, see Plank Energy. From a certain point of view, cars' gas gauges already commonly use 1 to denote a tank's maximum volume: Empty means 0, then come fractions ¼, ½, and ¾, and then Full means 1. Of course, these numbers correspond to different real volume measurements between different makes of car. However, it is unclear why the units used to measure the capacity of individual gas tanks would matter to highway engineers, who are primarily concerned with the safety of the roads those vehicles drive on, not how they operate.

Transcript

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[Two highway signs stand along a road with mountains in the background. One wide sign reads "NEXT EXIT" above a number starting with 1,390 followed by around thirty six zeros (some zeros are blocked by post of taller sign). A second, taller sign reads "SPEED LIMIT" above the number 0.000000097.]

[Caption below the panel:] OUR LOCAL HIGHWAY DEPARTMENT IS SWITCHING TO PLANCK UNITS.

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Discussion

OK, well, my local highway department is switching to Scientific Planck units. Maybe they'd be better off with Engineering Planck units, though. JohnHawkinson (talk) 03:20, 25 August 2026 (UTC)

But "1.39×10³⁹" would fit both. 84.2.104.152 03:56, 25 August 2026 (UTC)

65 meters per hour seems kind of slow 198.84.136.233 03:23, 25 August 2026 (UTC)

Agreed. I tried changing m/h to mph but my edit doesn't stick. Martin (talk) 03:35, 25 August 2026 (UTC)
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