3174: Bridge Clearance - Revision history

Sturmovik: /* Explanation */ Fixed link

2025-12-10T16:55:18Z

‎Explanation: Fixed link

Sturmovik: /* Explanation */ Changed wording

2025-12-10T16:54:07Z

‎Explanation: Changed wording

71.179.132.189: /* It is unproven that there is a mobial space elevator */

2025-12-09T18:13:30Z

‎It is unproven that there is a mobial space elevator

Sturmovik: /* Explanation */

2025-12-09T14:36:26Z

‎Explanation

Sturmovik: /* Explanation */ Improved wording

2025-12-09T14:24:42Z

‎Explanation: Improved wording

Sturmovik at 14:19, 9 December 2025

2025-12-09T14:19:58Z

Sturmovik: /* Explanation */

2025-12-09T14:16:49Z

‎Explanation

Sturmovik: /* Explanation */ Typo

2025-12-09T14:12:42Z

‎Explanation: Typo

Sturmovik at 14:11, 9 December 2025

2025-12-09T14:11:13Z

Sturmovik: /* Explanation */

2025-12-09T14:09:13Z

‎Explanation

@@ Line 12: / Line 12: @@
 Roads passing under bridges (or other overhead structures) often have signs indicating the "clearance" or lowest height of the bridge above the road, primarily to indicate to drivers of taller vehicles the potential hazard of driving underneath. In extreme cases warnings usually start with signs advising which routes to avoid starting down, but on most highways the signs are placed in the immediate vicinity of the offending structure. The comic shows one such sign with the low bridge in the background. An exit ramp, which conveniently avoids the bridge, has another sign has its own clearance information that, while technically accurate, is humorously pointless in the XKCD style as it is unlikely that a road vehicle on Earth{{Citation needed}} will care about running into the edge of the {{w|observable universe}} (46 billion light years).
-In the context of the North American road network, 10 feet 6 inches would be considered to be dangerously low and present a condition that would be likely to rip the roof off typical tractor trailers and box trucks as those tend to have a height of 12 to 13.5 feet. While a "No Bridge" type of sign is not generally used for clearance information above 13.5 feet, in this case the second sign can be justified as an additional aid to over height traffic that an alternative does exist. The situation depicted in the comic most frequently exists in the situation of North American railroad level crossings.  In the in the early decades of motoring (1920 to 1950) an underpass could be built in a busy area that motor vehicles could use if the existing roads were blocked by a train. Because road trucking was less common, the underpasses often had lower clearances in the range of 8.5 to 12 feet which later proved to be inadequate. One example of this can be found in Greensboro, North Carolina where [https://www.google.com/maps/@36.067412,-79.789736,3a,53.2y,316.29h,85.38t/data=!3m7!1e1!3m5!1saUzKZ66QfyUNXBY9DOe1og!2e0!6shttps:%2F%2Fstreetviewpixels-pa.googleapis.com%2Fv1%2Fthumbnail%3Fcb_client%3Dmaps_sv.tactile%26w%3D900%26h%3D600%26pitch%3D4.617549958018117%26panoid%3DaUzKZ66QfyUNXBY9DOe1og%26yaw%3D316.2907152075811!7i16384!8i8192!5m1!1e1?entry=ttu&g_ep=EgoyMDI1MTIwMi4wIKXMDSoASAFQAw%3D%3D| Elm Street crosses the former Southern Railway main line] and the bypass route has an 11 foot clearance. Although some early motor parkways do have bridge clearances in the vicinity of 10.5 feet, those routes were designed exclusively for passenger cars and have blanket restrictions on large and/or commercial vehicles.
+In the context of the North American road network, 10 feet 6 inches would be considered to be dangerously low and present a condition that would be likely to rip the roof off typical tractor trailers and box trucks as those tend to have a height of 12 to 13.5 feet. While a "No Bridge" type of sign is not generally used for clearance information above 13.5 feet, in this case the second sign can be justified as an additional aid to over height traffic that an alternative does exist. The situation depicted in the comic most frequently exists in the situation of North American railroad level crossings.  In the in the early decades of motoring (1920 to 1950) an underpass could be built in a busy area that motor vehicles could use if the existing roads were blocked by a train. Because road trucking was less common, the underpasses often had lower clearances in the range of 8.5 to 12 feet which later proved to be inadequate. One example of this can be found in Greensboro, North Carolina where [https://www.google.com/maps/@36.0684464,-79.7905775,3a,48.5y,158.3h,90.69t/data=!3m7!1e1!3m5!1sGpvq3bTrLDrc7ODxC07Bkw!2e0!6shttps:%2F%2Fstreetviewpixels-pa.googleapis.com%2Fv1%2Fthumbnail%3Fcb_client%3Dmaps_sv.tactile%26w%3D900%26h%3D600%26pitch%3D-0.6863818786752063%26panoid%3DGpvq3bTrLDrc7ODxC07Bkw%26yaw%3D158.2953474294634!7i16384!8i8192!5m1!1e1?entry=ttu&g_ep=EgoyMDI1MTIwNy4wIKXMDSoKLDEwMDc5MjA2N0gBUAM%3D| Elm Street crosses the former Southern Railway main line] and the bypass route has an 11 foot clearance. Although some early motor parkways do have bridge clearances in the vicinity of 10.5 feet, those routes were designed exclusively for passenger cars and have blanket restrictions on large and/or commercial vehicles.
 The title text references the fact that the Moon periodically passes over the road (or, from a different point of view, the road passes under the Moon). This implies that the road lies between {{w|Orbit of the Moon#Inclination|latitudes approximately 28.5° N and S}}. The Moon passes over any given longitude almost daily ({{w|Sidereal time|roughly every 24 hours}} but shifted by the Moon's own {{w|Lunar month#Sidereal month|slower motion}}). Whenever the Moon passes overhead, the theoretical clearance reduces to the distance between Earth and the Moon (around 225-250,000 miles or 360-400,000 km) and the same pedantic highway department would likely feel inclined to dynamically update the sign to remain technically correct at all times. This would be theoretically practical with active signage and some basic programming.

@@ Line 12: / Line 12: @@
 Roads passing under bridges (or other overhead structures) often have signs indicating the "clearance" or lowest height of the bridge above the road, primarily to indicate to drivers of taller vehicles the potential hazard of driving underneath. In extreme cases warnings usually start with signs advising which routes to avoid starting down, but on most highways the signs are placed in the immediate vicinity of the offending structure. The comic shows one such sign with the low bridge in the background. An exit ramp, which conveniently avoids the bridge, has another sign has its own clearance information that, while technically accurate, is humorously pointless in the XKCD style as it is unlikely that a road vehicle on Earth{{Citation needed}} will care about running into the edge of the {{w|observable universe}} (46 billion light years).
-In the context of the North American road network, 10 feet 6 inches would be considered to be dangerously low and present a condition that would be likely to rip the roof off typical tractor trailers and box trucks as those tend to have a height of 12 to 13.5 feet. While a "No Bridge" type of sign is not generally used for clearance information above 13.5 feet, in this case the second sign can be justified as an additional aid to over height traffic that an alternative does exist. The situation depicted in the comic most frequently exists in the situation of North American railroad level crossings that were partly replaced in the early days of motoring (1920 to 1950) before truck transport became widespread. In the case the crossing is blocked by a train, cars will have free use of the underpass while trucks would need to wait. One example of this can be found in Greensboro, North Carolina where [https://www.google.com/maps/@36.067412,-79.789736,3a,53.2y,316.29h,85.38t/data=!3m7!1e1!3m5!1saUzKZ66QfyUNXBY9DOe1og!2e0!6shttps:%2F%2Fstreetviewpixels-pa.googleapis.com%2Fv1%2Fthumbnail%3Fcb_client%3Dmaps_sv.tactile%26w%3D900%26h%3D600%26pitch%3D4.617549958018117%26panoid%3DaUzKZ66QfyUNXBY9DOe1og%26yaw%3D316.2907152075811!7i16384!8i8192!5m1!1e1?entry=ttu&g_ep=EgoyMDI1MTIwMi4wIKXMDSoASAFQAw%3D%3D| Elm Street crosses the former Southern Railway main line] and the bypass route has an 11 foot clearance. Although some early motor parkways do have bridge clearances in the vicinity of 10.5 feet, those routes were designed exclusively for passenger cars and have blanket restrictions on large and/or commercial vehicles.
+In the context of the North American road network, 10 feet 6 inches would be considered to be dangerously low and present a condition that would be likely to rip the roof off typical tractor trailers and box trucks as those tend to have a height of 12 to 13.5 feet. While a "No Bridge" type of sign is not generally used for clearance information above 13.5 feet, in this case the second sign can be justified as an additional aid to over height traffic that an alternative does exist. The situation depicted in the comic most frequently exists in the situation of North American railroad level crossings.  In the in the early decades of motoring (1920 to 1950) an underpass could be built in a busy area that motor vehicles could use if the existing roads were blocked by a train. Because road trucking was less common, the underpasses often had lower clearances in the range of 8.5 to 12 feet which later proved to be inadequate. One example of this can be found in Greensboro, North Carolina where [https://www.google.com/maps/@36.067412,-79.789736,3a,53.2y,316.29h,85.38t/data=!3m7!1e1!3m5!1saUzKZ66QfyUNXBY9DOe1og!2e0!6shttps:%2F%2Fstreetviewpixels-pa.googleapis.com%2Fv1%2Fthumbnail%3Fcb_client%3Dmaps_sv.tactile%26w%3D900%26h%3D600%26pitch%3D4.617549958018117%26panoid%3DaUzKZ66QfyUNXBY9DOe1og%26yaw%3D316.2907152075811!7i16384!8i8192!5m1!1e1?entry=ttu&g_ep=EgoyMDI1MTIwMi4wIKXMDSoASAFQAw%3D%3D| Elm Street crosses the former Southern Railway main line] and the bypass route has an 11 foot clearance. Although some early motor parkways do have bridge clearances in the vicinity of 10.5 feet, those routes were designed exclusively for passenger cars and have blanket restrictions on large and/or commercial vehicles.
 The title text references the fact that the Moon periodically passes over the road (or, from a different point of view, the road passes under the Moon). This implies that the road lies between {{w|Orbit of the Moon#Inclination|latitudes approximately 28.5° N and S}}. The Moon passes over any given longitude almost daily ({{w|Sidereal time|roughly every 24 hours}} but shifted by the Moon's own {{w|Lunar month#Sidereal month|slower motion}}). Whenever the Moon passes overhead, the theoretical clearance reduces to the distance between Earth and the Moon (around 225-250,000 miles or 360-400,000 km) and the same pedantic highway department would likely feel inclined to dynamically update the sign to remain technically correct at all times. This would be theoretically practical with active signage and some basic programming.

@@ Line 10: / Line 10: @@
 ==Explanation==
-Roads passing under bridges (or other overhead structures) often have signs indicating the "clearance" or lowest height of the bridge above the road, primarily to indicate to drivers of taller vehicles the potential hazard of driving underneath. In extreme cases warnings usually start with signs advising which routes to avoid starting down, but on most highways the signs are placed in the immediate vicinity of the offending structure. The comic shows one such sign with the low bridge in the background. An exit ramp, which conveniently avoids the bridge, has another sign has its own clearance information that, while technically accurate, is humorously pointless in the XKCD style as it is unlikely that a road vehicle on Earth will care about running into the edge of the {{w|observable universe}} (46 billion light years).
+Roads passing under bridges (or other overhead structures) often have signs indicating the "clearance" or lowest height of the bridge above the road, primarily to indicate to drivers of taller vehicles the potential hazard of driving underneath. In extreme cases warnings usually start with signs advising which routes to avoid starting down, but on most highways the signs are placed in the immediate vicinity of the offending structure. The comic shows one such sign with the low bridge in the background. An exit ramp, which conveniently avoids the bridge, has another sign has its own clearance information that, while technically accurate, is humorously pointless in the XKCD style as it is unlikely that a road vehicle on Earth{{Citation needed}} will care about running into the edge of the {{w|observable universe}} (46 billion light years).
 In the context of the North American road network, 10 feet 6 inches would be considered to be dangerously low and present a condition that would be likely to rip the roof off typical tractor trailers and box trucks as those tend to have a height of 12 to 13.5 feet. While a "No Bridge" type of sign is not generally used for clearance information above 13.5 feet, in this case the second sign can be justified as an additional aid to over height traffic that an alternative does exist. The situation depicted in the comic most frequently exists in the situation of North American railroad level crossings that were partly replaced in the early days of motoring (1920 to 1950) before truck transport became widespread. In the case the crossing is blocked by a train, cars will have free use of the underpass while trucks would need to wait. One example of this can be found in Greensboro, North Carolina where [https://www.google.com/maps/@36.067412,-79.789736,3a,53.2y,316.29h,85.38t/data=!3m7!1e1!3m5!1saUzKZ66QfyUNXBY9DOe1og!2e0!6shttps:%2F%2Fstreetviewpixels-pa.googleapis.com%2Fv1%2Fthumbnail%3Fcb_client%3Dmaps_sv.tactile%26w%3D900%26h%3D600%26pitch%3D4.617549958018117%26panoid%3DaUzKZ66QfyUNXBY9DOe1og%26yaw%3D316.2907152075811!7i16384!8i8192!5m1!1e1?entry=ttu&g_ep=EgoyMDI1MTIwMi4wIKXMDSoASAFQAw%3D%3D| Elm Street crosses the former Southern Railway main line] and the bypass route has an 11 foot clearance. Although some early motor parkways do have bridge clearances in the vicinity of 10.5 feet, those routes were designed exclusively for passenger cars and have blanket restrictions on large and/or commercial vehicles.

@@ Line 12: / Line 12: @@
 Roads passing under bridges (or other overhead structures) often have signs indicating the "clearance" or lowest height of the bridge above the road, primarily to indicate to drivers of taller vehicles the potential hazard of driving underneath. In extreme cases warnings usually start with signs advising which routes to avoid starting down, but on most highways the signs are placed in the immediate vicinity of the offending structure. The comic shows one such sign with the low bridge in the background. An exit ramp, which conveniently avoids the bridge, has another sign has its own clearance information that, while technically accurate, is humorously pointless in the XKCD style as it is unlikely that a road vehicle on Earth will care about running into the edge of the {{w|observable universe}} (46 billion light years).
-In the context of the North American road network, 10 feet 6 inches would be considered to be dangerously low and present a condition that would be likely to rip the roof off typical tractor trailers and box trucks as those tend to have a height of 12 to 13.5 feet. While a "No Bridge" type of sign is not generally used for clearance information above 13.5 feet, in this case the second sign can be justified as an additional aid to over height traffic that an alternative does exist. The situation depicted in the comic most frequently exists in the situation of North American railroad level crossings that were partly replaced in the early days of motoring (1920 to 1950) before truck transport became widespread. In the case the crossing is blocked by a train, cars will have free use of the underpass while trucks would need to wait. One example of this can be found in Greensboro, North Carolina where [https://www.google.com/maps/@36.067412,-79.789736,3a,53.2y,316.29h,85.38t/data=!3m7!1e1!3m5!1saUzKZ66QfyUNXBY9DOe1og!2e0!6shttps:%2F%2Fstreetviewpixels-pa.googleapis.com%2Fv1%2Fthumbnail%3Fcb_client%3Dmaps_sv.tactile%26w%3D900%26h%3D600%26pitch%3D4.617549958018117%26panoid%3DaUzKZ66QfyUNXBY9DOe1og%26yaw%3D316.2907152075811!7i16384!8i8192!5m1!1e1?entry=ttu&g_ep=EgoyMDI1MTIwMi4wIKXMDSoASAFQAw%3D%3D| Elm Street crosses the former Southern Railway main line] and the bypass route has an 11 foot clearance.
+In the context of the North American road network, 10 feet 6 inches would be considered to be dangerously low and present a condition that would be likely to rip the roof off typical tractor trailers and box trucks as those tend to have a height of 12 to 13.5 feet. While a "No Bridge" type of sign is not generally used for clearance information above 13.5 feet, in this case the second sign can be justified as an additional aid to over height traffic that an alternative does exist. The situation depicted in the comic most frequently exists in the situation of North American railroad level crossings that were partly replaced in the early days of motoring (1920 to 1950) before truck transport became widespread. In the case the crossing is blocked by a train, cars will have free use of the underpass while trucks would need to wait. One example of this can be found in Greensboro, North Carolina where [https://www.google.com/maps/@36.067412,-79.789736,3a,53.2y,316.29h,85.38t/data=!3m7!1e1!3m5!1saUzKZ66QfyUNXBY9DOe1og!2e0!6shttps:%2F%2Fstreetviewpixels-pa.googleapis.com%2Fv1%2Fthumbnail%3Fcb_client%3Dmaps_sv.tactile%26w%3D900%26h%3D600%26pitch%3D4.617549958018117%26panoid%3DaUzKZ66QfyUNXBY9DOe1og%26yaw%3D316.2907152075811!7i16384!8i8192!5m1!1e1?entry=ttu&g_ep=EgoyMDI1MTIwMi4wIKXMDSoASAFQAw%3D%3D| Elm Street crosses the former Southern Railway main line] and the bypass route has an 11 foot clearance. Although some early motor parkways do have bridge clearances in the vicinity of 10.5 feet, those routes were designed exclusively for passenger cars and have blanket restrictions on large and/or commercial vehicles.
 The title text references the fact that the Moon periodically passes over the road (or, from a different point of view, the road passes under the Moon). This implies that the road lies between {{w|Orbit of the Moon#Inclination|latitudes approximately 28.5° N and S}}. The Moon passes over any given longitude almost daily ({{w|Sidereal time|roughly every 24 hours}} but shifted by the Moon's own {{w|Lunar month#Sidereal month|slower motion}}). Whenever the Moon passes overhead, the theoretical clearance reduces to the distance between Earth and the Moon (around 225-250,000 miles or 360-400,000 km) and the same pedantic highway department would likely feel inclined to dynamically update the sign to remain technically correct at all times. This would be theoretically practical with active signage and some basic programming.

@@ Line 10: / Line 10: @@
 ==Explanation==
-Roads passing under bridges (or other overhead structures) often have signs indicating the "clearance" or lowest height of the bridge above the road, primarily to indicate to drivers of taller vehicles the potential hazard of driving underneath. In extreme cases warnings usually start with signs advising which routes to avoid starting down, but on most highways the signs are placed in the immediate vicinity of the offending structure. The comic shows one such sign with the low bridge in the background. An exit ramp, which conveniently avoids the bridge, has another sign has its own clearance information that, while technically accurate, is humorously pointless in the XKCD style as it is unlikely that a road vehicle on Earth will care about running into the edge of the observable universe.
+Roads passing under bridges (or other overhead structures) often have signs indicating the "clearance" or lowest height of the bridge above the road, primarily to indicate to drivers of taller vehicles the potential hazard of driving underneath. In extreme cases warnings usually start with signs advising which routes to avoid starting down, but on most highways the signs are placed in the immediate vicinity of the offending structure. The comic shows one such sign with the low bridge in the background. An exit ramp, which conveniently avoids the bridge, has another sign has its own clearance information that, while technically accurate, is humorously pointless in the XKCD style as it is unlikely that a road vehicle on Earth will care about running into the edge of the {{w|observable universe}} (46 billion light years).
-Note that 10 feet 6 inches would be considered to be an dangerously low bridge that would be likely to rip the roof off most North American tractor trailers and box trucks as those tend to have a height of 12 to 13.5 feet. While a "No Bridge" type of sign is not generally used for clearance information above 13.5 feet, in this case the second sign can be justified as an additional aid to over height traffic that an alternative does exist. The situation depicted in the comic most frequently exists in the situation of North American railroad level crossings that were partly replaced in the early days of motoring (1920 to 1950) before truck transport became widespread. In the case the crossing is blocked by a train, cars will have free use of the underpass while trucks would need to wait. One example of this can be found in Greensboro, North Carolina where [https://www.google.com/maps/@36.067412,-79.789736,3a,53.2y,316.29h,85.38t/data=!3m7!1e1!3m5!1saUzKZ66QfyUNXBY9DOe1og!2e0!6shttps:%2F%2Fstreetviewpixels-pa.googleapis.com%2Fv1%2Fthumbnail%3Fcb_client%3Dmaps_sv.tactile%26w%3D900%26h%3D600%26pitch%3D4.617549958018117%26panoid%3DaUzKZ66QfyUNXBY9DOe1og%26yaw%3D316.2907152075811!7i16384!8i8192!5m1!1e1?entry=ttu&g_ep=EgoyMDI1MTIwMi4wIKXMDSoASAFQAw%3D%3D| Elm Street crosses the former Southern Railway main line] and the bypass route has an 11 foot clearance.
+In the context of the North American road network, 10 feet 6 inches would be considered to be dangerously low and present a condition that would be likely to rip the roof off typical tractor trailers and box trucks as those tend to have a height of 12 to 13.5 feet. While a "No Bridge" type of sign is not generally used for clearance information above 13.5 feet, in this case the second sign can be justified as an additional aid to over height traffic that an alternative does exist. The situation depicted in the comic most frequently exists in the situation of North American railroad level crossings that were partly replaced in the early days of motoring (1920 to 1950) before truck transport became widespread. In the case the crossing is blocked by a train, cars will have free use of the underpass while trucks would need to wait. One example of this can be found in Greensboro, North Carolina where [https://www.google.com/maps/@36.067412,-79.789736,3a,53.2y,316.29h,85.38t/data=!3m7!1e1!3m5!1saUzKZ66QfyUNXBY9DOe1og!2e0!6shttps:%2F%2Fstreetviewpixels-pa.googleapis.com%2Fv1%2Fthumbnail%3Fcb_client%3Dmaps_sv.tactile%26w%3D900%26h%3D600%26pitch%3D4.617549958018117%26panoid%3DaUzKZ66QfyUNXBY9DOe1og%26yaw%3D316.2907152075811!7i16384!8i8192!5m1!1e1?entry=ttu&g_ep=EgoyMDI1MTIwMi4wIKXMDSoASAFQAw%3D%3D| Elm Street crosses the former Southern Railway main line] and the bypass route has an 11 foot clearance.
 The title text references the fact that the Moon periodically passes over the road (or, from a different point of view, the road passes under the Moon). This implies that the road lies between {{w|Orbit of the Moon#Inclination|latitudes approximately 28.5° N and S}}. The Moon passes over any given longitude almost daily ({{w|Sidereal time|roughly every 24 hours}} but shifted by the Moon's own {{w|Lunar month#Sidereal month|slower motion}}). Whenever the Moon passes overhead, the theoretical clearance reduces to the distance between Earth and the Moon (around 225-250,000 miles or 360-400,000 km) and the same pedantic highway department would likely feel inclined to dynamically update the sign to remain technically correct at all times. This would be theoretically practical with active signage and some basic programming.

@@ Line 12: / Line 12: @@
 Roads passing under bridges (or other overhead structures) often have signs indicating the "clearance" or lowest height of the bridge above the road, primarily to indicate to drivers of taller vehicles the potential hazard of driving underneath. In extreme cases warnings usually start with signs advising which routes to avoid starting down, but on most highways the signs are placed in the immediate vicinity of the offending structure. The comic shows one such sign with the low bridge in the background. An exit ramp, which conveniently avoids the bridge, has another sign has its own clearance information that, while technically accurate, is humorously pointless in the XKCD style as it is unlikely that a road vehicle on Earth will care about running into a star in a galaxy far far away.
-Note that 10 feet 6 inches would be considered to be an dangerously low bridge that would be likely to rip the roof off most North American tractor trailers and box trucks that typically have a height of 12 to 13.5 feet. While a "No Bridge" type of sign is not generally used for clearance information above 13.5 feet, in this case the second sign can be justified as an additional aid to over height traffic that an alternative does exist. The situation depicted in the comic most frequently exists in the situation of North American railroad level crossings that were partly replaced in the early days of motoring (1920 to 1950) before truck transport became widespread. In the case the crossing is blocked by a train, cars will have free use of the underpass while trucks would need to wait. One example of this can be found in Greensboro, North Carolina where [https://www.google.com/maps/@36.067412,-79.789736,3a,53.2y,316.29h,85.38t/data=!3m7!1e1!3m5!1saUzKZ66QfyUNXBY9DOe1og!2e0!6shttps:%2F%2Fstreetviewpixels-pa.googleapis.com%2Fv1%2Fthumbnail%3Fcb_client%3Dmaps_sv.tactile%26w%3D900%26h%3D600%26pitch%3D4.617549958018117%26panoid%3DaUzKZ66QfyUNXBY9DOe1og%26yaw%3D316.2907152075811!7i16384!8i8192!5m1!1e1?entry=ttu&g_ep=EgoyMDI1MTIwMi4wIKXMDSoASAFQAw%3D%3D|Elm Street crosses the former Southern Railway main line] where the bypass route has an 11 foot clearance.
+Note that 10 feet 6 inches would be considered to be an dangerously low bridge that would be likely to rip the roof off most North American tractor trailers and box trucks that typically have a height of 12 to 13.5 feet. While a "No Bridge" type of sign is not generally used for clearance information above 13.5 feet, in this case the second sign can be justified as an additional aid to over height traffic that an alternative does exist. The situation depicted in the comic most frequently exists in the situation of North American railroad level crossings that were partly replaced in the early days of motoring (1920 to 1950) before truck transport became widespread. In the case the crossing is blocked by a train, cars will have free use of the underpass while trucks would need to wait. One example of this can be found in Greensboro, North Carolina where [https://www.google.com/maps/@36.067412,-79.789736,3a,53.2y,316.29h,85.38t/data=!3m7!1e1!3m5!1saUzKZ66QfyUNXBY9DOe1og!2e0!6shttps:%2F%2Fstreetviewpixels-pa.googleapis.com%2Fv1%2Fthumbnail%3Fcb_client%3Dmaps_sv.tactile%26w%3D900%26h%3D600%26pitch%3D4.617549958018117%26panoid%3DaUzKZ66QfyUNXBY9DOe1og%26yaw%3D316.2907152075811!7i16384!8i8192!5m1!1e1?entry=ttu&g_ep=EgoyMDI1MTIwMi4wIKXMDSoASAFQAw%3D%3D| Elm Street crosses the former Southern Railway main line] where the bypass route has an 11 foot clearance.
 The title text references the fact that the Moon periodically passes over the road (or, from a different point of view, the road passes under the Moon). This implies that the road lies between {{w|Orbit of the Moon#Inclination|latitudes approximately 28.5° N and S}}. The Moon passes over any given longitude almost daily ({{w|Sidereal time|roughly every 24 hours}} but shifted by the Moon's own {{w|Lunar month#Sidereal month|slower motion}}). Whenever the Moon passes overhead, the theoretical clearance reduces to the distance between Earth and the Moon (around 225-250,000 miles or 360-400,000 km) and the same pedantic highway department would likely feel inclined to dynamically update the sign to remain technically correct at all times. This would be theoretically practical with active signage and some basic programming.