How high is that overpass -- REALLY?!

[Oldyeller]

Originally Posted by lawdog71

Purchase a copy of the Rand McNally Motor Carrier Road Atlas, they list low overpass clearances.


I'm a trucker and we use that resource all the time.


~s

I think I saw that recommended in one of the previous threads on this subject I found in my search. If I actually get out in my bus I'll probably buy one, thanks.

[Deb&John]

[Great info here- I didn’t know about the color code- (don’t worry, I’m just a passenger!) But you’ve led me to add my question to the original question: What about road resurfacing? There have been several times I’ve seen the road get resurfaced- potentially adding several inches of concrete or blacktop, yet the sign remains with the original measurement...

And since we’re on the topic- how DO you accurately measure Your height? How DO road crews accurately measure the clearance?
All this makes me want to stay a passenger!

QUOTE=Sehnsucht;456913]Not consistent but as a general rule:

If the clearance sign is white background, that's regulatory. Most likely they've measured the lowest point of the overpass and compensating for the road grade you can trust that.

If the clearance sign is yellow background, that's advisory. The clearance has been estimated or could vary depending on how you approach it. For instance, if the overpass is arched, you may be able to make it through if you're in the middle of the arch (straddling lanes on a two-lane) but not if you maintain your own lane. Often times also if the lane is regulation but the shoulder is less, there might be a specific clearance sign with an arrow indicating where in the arch it is lower than standard clearance.

For semi trucks, the national standard has been 13ft 6inches since the early 80s. The STAA designated truck appropriate routes and adequate signage along those routes for anything that's below the standard. In the northeast specifically and in older cities in general, it takes a sharp eye and diligence to avoid getting on the 'wrong' route then encountering an impassible low clearance. And if you end up there, plan on paying multiple fines.

Based on the OP's assessment, I would not attempt any route where there's a known low clearance of 8ft 6inches. I wouldn't trust any full size bus to safely clear that. The problem is often not in the entrance but in the exit. An empty bus is probably taller in the back so it may not hit going in but could scrape on the way out. I watched a semi in Indianapolis who assumed because he fit going in he was safe but the 12'6" was on the exit side where the road grade climbs and the tractor starts up the grade before the trailer is out of the tunnel. It's entertaining to watch the middle of the roof just fold in on itself. Don't be that driver.[/QUOTE]

[Mountain Gnome]

Originally Posted by Deb&John

how DO you accurately measure Your height? How DO road crews accurately measure the clearance?

IDK, but I bet the clearance is measured with a telescoping pole.


As for your bus clearance, find a flat, level spot. Use a 3-foot bubble-level to make sure it is level. Park the bus there.


Get a 6-foot long strait stick. Put one end at the bus roof center, or on the top of the highest point (like a rooftop AC unit). Let the other end extend out past the side of the bus. Use a telescoping pole (or strap two strait sticks together with rope or whatnot and allow for adjustments) to hold up the end of the stick on the roof that sticks out past the side of the bus. Put your level on the top of the stick, and adjust the telescoping pole until the bubble-level is level. Then measure the telescoping pole length on the ground with a tape-measure. Assume a few inches of error from the ground not actually being perfectly flat or level.

[Sehnsucht]

I'll see if I can grab a few photos as I pass several overpasses in my weekly route which demonstrate this. Basically it seems SC specifically can't figure out how to remove their old signs so they spray paint over the old ones and post new ones next to it.

Most likely when the overpass is built the clearance is verified actually but then over time the lower road surface is repaved and/or milled and resurfaced so at that point the clearance is estimated based on how much surface was added/removed but they don't take the time or shut down the entire roadway just to conduct a new statutory measurement of the clearance. And it wouldn't just be one spot, they would need to measure in multiple places along the underside of the overpass to ensure the absolute lowest point of clearance is verified and posted, otherwise if there is a collision they can't go back and accuse the driver of negligence.

This is partly what happened a few years back which collapsed the Skagit River Bridge on I-5 in Washington State. Yes there was failures by the pilot car driver who didn't radio back fast enough to stop the oversized load but also the incorrectly documented clearance led the carrier to believe crossing that bridge was appropriate when in fact they had inaccurate or outdated information concerning the bridge's clearance and/or weight capacity. When they whacked enough of the cross members to sufficiently weaken the bridge, the span succumbed and collapsed. Then the state sued the carrier for the cost to replace the bridge. The carrier's defense was the documented clearance was inaccurate.