Talk:3174: Bridge Clearance

But when the moon is directly overhead they also have to edit the contents of the sign Mathmaster (talk)

The Moon being overhead only applies to places in latitudes roughly between 28.5 degrees N and S, at its absolute most extreme inclinations. So, for the contiiguous US, that potentially affects only roads in some bits of Florida and Texas.

Louisiana's most southern point is very close to that, such that the 'upper limb' of our satellite would 'overhead' an additional quarter of a degree of latitude, taking in this spot and a bit more. But that location is also an island. Port Fourchon, Louisiana, seems to be the most southerly stretch of regular (mainland) road in that state, and that's still just too far north to be affected. 78.144.255.82 23:10, 28 November 2025 (UTC)

Note how the second sign extends off the panel, presumably with a warning further up for any vehicles under clearance. That’s quite the space elevator. KelOfTheStars! (talk) 01:21, 29 November 2025 (UTC)

Also note that in latitudes where the moon could possibly be directly overhead, the sun could also be directly overhead. This would also necessitate a change to the sign 24.210.252.188 02:56, 29 November 2025 (UTC)

(Moon tilt on top of Earth tilt makes the all-seasons "Sun overhead" a narrower band than the potential "Moon-overhead", i.e. Tropic Of Capricorn to Tropic Of Cancer).

For an even greater range, and lower clearance, consider the ISS. Then there's the Starlink/etc constellation 'mesh' of orbits that deliberately stretches further out. Or indeed polar-(/near-polar-)orbits for Earth Observation (Sun-synchronous orbits, slightly off polar, typically can be directly above anything up to 82-ish° N/S, being 98° and retrograde.

And clearances of GSOs (there will be locations where sufficiently geostationary satellites are pretty much perpetual, though mere geosynchronous ones may have daily (or twice-daily, on the crux of the figure-of-8 ground track) 'exposure') are so much greater than what the LEO ones would.

A particular favourite of the Russian civil/military programmes are highly eccentric (and oblique) to service the kind of latitudes they want more loiter (slow, and far away) or passage (near, but rapid) over, often in teams of craft spread across the track to pass coverage over to another when one of them zooms on out of the desired 'sweet spot'... "Tundra Orbits", I think it is? So accounting for them might involve vastly varying heights (though usually similar, overhead to overhead, barring any ascending-/descending-track differences) over a greater-than-average spread of latitudes (but still less than pure 90°-polar would, which is potentially over everywhere at some time or another). 82.132.237.174 14:06, 29 November 2025 (UTC)

When I first read the title text I thought it was talking about the tide's effect on the height of the bridge. Barmar (talk) 03:55, 29 November 2025 (UTC)

How old is the sign that needs to he updated every day? These days they have automated signs for things like travel time to important exits, that type of system could easily be used to keep the clearance up-to-date. Barmar (talk) 03:59, 29 November 2025 (UTC)

It'll cost more to at least maintain a changable sign. Perhaps power connection (unless solar+battery is enough), probably data connection (push- or pull- reconfiguration, unless relying upon continually internally calculated via RTC and the appropriate ephemera). It might not need to be visited each day, but periodic checks are going to be more than checking it hasn't been overly pierced by buckshot (or being told it's been flattened by a carelessly driven vehicle), and other charges will apply. Especially if you're covering every few yards (even hundreds of yards) of road with individually personalised warnings for that particular stretch. 82.132.237.174 14:06, 29 November 2025 (UTC)

> clearance of 10 feet and 6 inches, which is a realistic clearance..... Anything less than 13'6" (in the US) will get hit frequently. Yes, we know some bridges that get hit frequently. --PRR (talk) 06:42, 29 November 2025 (UTC)

It says realistic, not common. Storrow Drive, which should be very familiar to Randall, has a clearance of just 10 feet. --Coconut Galaxy (talk) 07:08, 29 November 2025 (UTC)