Hiya… how about having a mag mount CB areial whip on your cab roof set at 1 inch higher than your trailer.
this will rattle on the bridge if you was going to hit it. the ariel bends back and dosent break.
simple it worked for me almost 20 years. ok i had the same trailer on most of the time.
saying that all out trailers was the same height.made me mad hitting some low twigs that whent up over
the roof, as i drove down B roads.
John
Sidevalve:
weeto:
.So, did you also find out why some bridges have a warning sign and some have a prohibitive sign?
No… but it’s a good question and I’ll ask him.
And the answer is…
“From a quick read of the manual it would seem that the triangular warning signs should be used at arched bridges where the main danger is from vehicles striking the sides of the arch. The circular prohibitory sign should be used at non-arched bridges where strikes are likely at any point under the bridge.”
He goes on to say that he is sure that this advice is not always followed to the letter; the manual is apparently only a guide, which apparently makes for quite interesting reading.
Should anybody need the actual letter of the law it’s contained here;
I daresay that would put the world’s worst insomniac to sleep in minutes! 
it does occur to me that this info might well be of good use to some drivers who get into the mire with the authorities where road signs appear to be either misleading or ambivalent, or simply situated in the wrong place. Perhaps Admin could copy the links and put a sticky in the Legal section for reference?
I wonder if road undulations might make a difference to the height signed.
Always wary when approaching a bridge i’m going to be at maximum height for, at the wrong speed a mild dip in the road (taken at a different speed) might rebound the vehicle up over it normal height.
Fatboy slimslow:
Round prohibitive = NEVER approach, warning TRIANGLE = lower suspension
The question was, why they use both, we already know what they mean!
Fatboy slimslow:
Round prohibitive = NEVER approach, warning TRIANGLE = lower suspension
Must have been a triangle one on the south circular around kew, just by records office.
14ft 9 marked bridge, 14ft 7 trailer, approaching from South, heading up to m4, when sign lights up, “overheight vehicle, please turn back”, even though nowhere to turn, but that would have been another story. Dropped air out of unit suspension and sign went out, as I was in traffic, I also dropped air from trailer to be safe.
Went under without drama and just sorted air out again in the next London traffic jam.
Bit worrying when the sign lights up, even though you know your trailer will go under
That bridge at Wilton has always done that ever since it was installed approach from North use middle of road approach from South over height turn back and yet there is plenty of room for 13’ 2’’ trailers. First time it happened to me despite the fact id been going under it before i stopped and then a wagon and trailer much taller than me came through, so i thought must be a problem with the sensors. Makes you think though. Also worked for campany the other day driving a rigid with second man doing home deliveries, he says we can go down this road i say no its got a 12’ bridge he says our other driver always gets under i proceed with caution plenty of room underneath. ■■? 
Question…
Say you’re a cab hopper. Say the height indicator in the cab reads 14’ 8. Say you drive under a bridge that’s posted at 14’ 9.
Say you strike that bridge because, for example, the person who set the height indicator mis-measured it by an inch or two.
Who’s to blame? Instinct tells me that the driver would be to blame, because it’s technically his or her responsibility to ‘ensure’ the posted height of their vehicle is correct.
Javiatrix:
Question…Say you’re a cab hopper. Say the height indicator in the cab reads 14’ 8. Say you drive under a bridge that’s posted at 14’ 9.
Say you strike that bridge because, for example, the person who set the height indicator mis-measured it by an inch or two.
Who’s to blame? Instinct tells me that the driver would be to blame, because it’s technically his or her responsibility to ‘ensure’ the posted height of their vehicle is correct.
Your instinct is correct. It’s up to you to check; and it doesn’t just apply to artics either.
When I got my new 8-wheeler back in April, the indicator was set at 12’ 5"… looking round the wagon, as you do, it just didn’t LOOK right and I was uneasy about it, so I got the tape out and sure enough it was 12’ 6". The effect was probably enhanced by having a full-height sleeper cab but nevertheless I preferred to check rather than have the nagging doubt which only manifested itself the first time I went under a tight bridge. Only an inch but that can make a lot of difference as our wives are constantly telling us!
Moral of the story is if you get a new wagon it does no harm to double-check, for the sake of five minutes.
Here’s a thought; older drivers will remember the old loading gauge gantry which used to be a feature of railway goods yards back in the 1960’s.
With the advent of modern technology, it is not outside the wit of designers to come up with a computerised version of this, to be installed at the exit to a yard, which the driver has to acknowledge and correctly set before continuing onto the road. Yes, I hear you say, another step towards being a steering wheel attendant instead of a real driver; but a real driver would’ve checked it anyway. 
Sidevalve:
Javiatrix:
Question…Say you’re a cab hopper. Say the height indicator in the cab reads 14’ 8. Say you drive under a bridge that’s posted at 14’ 9.
Say you strike that bridge because, for example, the person who set the height indicator mis-measured it by an inch or two.
Who’s to blame? Instinct tells me that the driver would be to blame, because it’s technically his or her responsibility to ‘ensure’ the posted height of their vehicle is correct.
Your instinct is correct. It’s up to you to check; and it doesn’t just apply to artics either.
When I got my new 8-wheeler back in April, the indicator was set at 12’ 5"… looking round the wagon, as you do, it just didn’t LOOK right and I was uneasy about it, so I got the tape out and sure enough it was 12’ 6". The effect was probably enhanced by having a full-height sleeper cab but nevertheless I preferred to check rather than have the nagging doubt which only manifested itself the first time I went under a tight bridge. Only an inch but that can make a lot of difference as our wives are constantly telling us!
Moral of the story is if you get a new wagon it does no harm to double-check, for the sake of five minutes.
Here’s a thought; older drivers will remember the old loading gauge gantry which used to be a feature of railway goods yards back in the 1960’s.
With the advent of modern technology, it is not outside the wit of designers to come up with a computerised version of this, to be installed at the exit to a yard, which the driver has to acknowledge and correctly set before continuing onto the road. Yes, I hear you say, another step towards being a steering wheel attendant instead of a real driver; but a real driver would’ve checked it anyway.
DSV’s yard opposite the refinery has an electronic hight display on the outgate, but its not much use to me when it tells me that my trailer is 4.1!!!
Does my head in when I pull into a garage and the canopy or come to a bridge that is marked up at 4.5m and my trailer is 14’6" high!
Why are some marked up in metres when we still use imperial?