https://www.explainxkcd.com/wiki/api.php?action=feedcontributions&feedformat=atom&user=Pinkgothicexplain xkcd - User contributions [en]2026-04-16T11:37:36ZUser contributionsMediaWiki 1.30.0https://www.explainxkcd.com/wiki/index.php?title=3174:_Bridge_Clearance&diff=3927223174: Bridge Clearance2025-11-28T23:28:58Z<p>Pinkgothic: Fixed a typo ('highwa' -> 'highway')</p>
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<div>{{comic<br />
| number = 3174<br />
| date = November 28, 2025<br />
| title = Bridge Clearance<br />
| image = bridge_clearance_2x.png<br />
| imagesize = 450x233px<br />
| noexpand = true<br />
| titletext = A lot of the highway department's budget goes to adjusting the sign whenever the moon passes directly overhead.<br />
}}<br />
<br />
==Explanation==<br />
{{incomplete|This page was created BY A BRIDGE WITH NO CLEARANCE. Don't remove this notice too soon.}}<br />
Bridges will often have signs indicating the height of the bridge, primarily to indicate to taller vehicles the potential hazard of driving under them, sometimes along with {{w|Bridge strike#Passive devices|physical warning systems}} to alert unobservant drivers any imminent errors. In this comic, there is a bridge with one of these signs and 'sacrificial' bars, indicating a clearance of 10 feet and 6 inches, which is a normal clearance for a bridge to have. To its right, there's a sign which says "no bridge", indicating a clearance of 46 billion light years. This sign indicates a (default) clearance on this stretch of highway that is approximately equal to the radius of the observable universe. This is because there isn't any bridge or obstruction any lower than this particularly generous 'limit'.<br />
<br />
The title text references the fact that at times when the Moon passes over the road, the clearance would be reduced to the distance between Earth and the Moon, as any vehicle driving there would need to be shorter (than this ''still'' very generous limit), otherwise it could crash into the Moon. Both of these signs ignore the fact that vehicles cannot be large enough that either clearances would be something necessary to account for while driving.<br />
<br />
The title text says that the sign might crash into the Moon during certain times. However, they also need to adjust it for any stars, which would be easier if there were just people living on the sign and adjusting it with some smart mechanism.<br />
<br />
==Transcript==<br />
{{incomplete transcript|Don't remove this notice too soon.}}<br />
[:There is a road with a fork and one side that goes to the left has a sign. The one that goes forward has a bridge and a clearance sign.]<br />
<br />
[:left sign with bridge underlined, it has a horizontal line that is dotted with slashes.]<br />
<br />
Bridge<br />
<br />
Clearance<br />
<br />
10 ft 6 in<br />
<br />
[:right sign with No bridge underlined]<br />
<br />
No Bridge<br />
<br />
Clearance<br />
<br />
46+ Billion light years<br />
{{comic discussion}}<noinclude></div>Pinkgothic