How is Tunnel Height measured?

[ScottyGS]

Took the side roads on our trip last summer and passed a sign that said "Tunnel Ahead - 10 foot clearance".    Ok.. so that's getting close to our trailer height....   Approached very carefully and found that we had more that a few feet of clearance.   Not even close.   

Which led me to wonder....    Are tunnel heights measured to center?   Or, to the side?    Are there highway construction standards that measurements are supposed to conform to?    A lot of tunnels have a curved roof.... the Oliver is higher in the center than at the sides, so that should work for us.  

Inquiring minds want to know!    Any highway experts out there that can shed some light on this topic.   I did an internet search and now know more about measuring the airflow speed in a wind tunnel than I ever wanted to know.   But not so much on this. 

Thanks in Advance,

Scotty

[Steph and Dud B]

We have seen curved tunnels with signs that specify the heights at both the edges and the center. 

[John E Davies]

Posted height is supposed to be the minimum, so it would be directly over the edge of the pavement. Look for damaged concrete from truckers who ignored that😬.

For a two lane tunnel I don’t worry much, I just shift over to the middle a little. Here is one from Colorado National  Monument:

Those single lane low ceiling round tunnels are another thing entirely, they can be butt clenching, pardon the allusion.

John Davies 

Spokane WA

[Dave Mazone]

Being a former big rig driver, I was taught that YOU are responsible for the clearance, regardless of the signs. Experience showed me that those measurements are typically the low points, whether to the side of the bridge or within the tunnel. However, don't assume that they update the signs when they've done road maintenance (like resurfacing). I have seen signs under my 13-6 that I determined I had plenty of room (but was sweating bullets nonetheless) and bridges it said I'd clear, but I wouldn't try.

Consider getting a retractable pole and mark the max height of the trailer on it. Stop and poke around when in doubt...60, 75, 85 grand is a big personal gamble! Safe journies.

[John E Davies]

1 hour ago, Dave Mazone said:

Stop and poke around when in doubt...60, 75, 85 grand is a big personal gamble! Safe journies.

I figure that my solar panel “curb feeler” will save the hull itself. So, maybe $5,000 to repair that? As long as it doesn't wipe off the air conditioner too.

I have a 14 foot tall door on my RV bay, the first year that I had the Ollie, I used to just raise the door part way, to save wear and tear on the door springs. It worked great until the time I misjudged the height. As I was pulling forward the front of the hull caught the bottom edge of the door and trashed two full panels. I backed up and unhitched and kicked the door more or less into shape so I could close it again. The overhead door guy was unimpressed. He has seen everything. The repair was around $800, if I recall correctly.  I think my wife was not amused. 

The Ollie damage was confined to the sewer waste cap, which ended up on the floor, and some light scuffing on the gelcoat. Cost of that repair was less than $5. Ollies are tough, as long as you stop in time (as soon as you hear that horrible SCRIIIIIITCH!)

Now I always raise the door to its full height.

Back when I used to ride bikes and carry them on the roof of my car, I would tie a bright orange surveyors tape flag on the garage door, to remind me to not drive in yet. That worked well.

John Davies

Spokane WA

[AlbertNTerri]

My solution back from my trucking days was simple, i set my CB antenna (mounted to my mirror bracket) to about 2 inches taller than my trailer and adjusted the height whenever I changed trailers. I'd slow down and if the antenna hit then I knew I had less then 2 inches clearance (or possibly none!). I hadn't thought about it recently, but it wouldn't be difficult to mount some type of "measuring stick" to the truck to accomplish the same thing. That said, I've not seen many overpasses or tunnels that are less than 10 feet so my backup plan has always been to open the driver's door, with the vehicle in gear and my foot hovering over the brake, I stand in the open doorway while watching the top of the trailer and if it looks like it's going to hit I jam on the break (which in the old days resulted in stalling the truck but sparing an accident). Even if it has enough clearance if you hit a bump in the tunnel or under the bridge, it could cause the trailer to jump high enough to crunch the roof so it's always better to creep through those places slowly and like you said, it generally results in testing "sphinter control." 

[ScottyGS]

1 hour ago, albert said:

my backup plan has always been to open the driver's door, with the vehicle in gear and my foot hovering over the brake, I stand in the open doorway while watching the top of the trailer and if it looks like it's going to hit I jam on the break 

I made Donna get out and look.   But that's a good plan if travelling solo.   People behind you may get pissed off but would be more inconvenienced if you jammed your rig in the tunnel. 

[John E Davies]

4 hours ago, albert said:

My solution back from my trucking days was simple, i set my CB antenna (mounted to my mirror bracket) to about 2 inches taller than my trailer and adjusted the height whenever I changed trailers. 

That is a great idea, as long as you are adjusting the support bracket. You aren't supposed to adjust the actual rod vertically, that is for fine tuning the SWR (maximizing the signal). If you have one mounted to use as a curb feeler, that wouldn’t matter. I still carry a CB, it’s a portable one with magnetic base, all of which is broken down and stored in my emergency box. I think the last time I actually used one was about 1980 😳 I bought it in case I ever ended up in a 4wd convoy, but that has never happened. I suppose I should donate it to charity. Do CBs have any cash value now?

John Davies

Spokane WA

 

[Steph and Dud B]

We still use CBs, mostly when traveling with friends, or if Steph is in her car behind the trailer. A full power CB with a roof antenna has much better range than the little FRS radios.  The truckers have mostly abandoned the channels, so you pretty much have the airspace to yourselves. And, if there's a highway incident, some truckers still get on 19 to see what's going on, so it can be a good source of information. The CBs we have are similar to John's. They plug into a cigarette lighter socket and have mag-mount antennas so we don't have them in the truck when not needed. https://www.amazon.com/Midland-75-822-Channel-CB-Way-Radio/dp/B00000K2YR

[John E Davies]

1 hour ago, Steph and Dud B said:

https://www.amazon.com/Midland-75-822-Channel-CB-Way-Radio/dp/B00000K2YR

That is mine, I like the design and features, it gets good ratings.

John Davies

Spokane WA