Caravans and Trucks Sharing the Road.

Submitted: Saturday, Mar 03, 2012 at 02:39
ThreadID: 127910 Views:13891 Replies:11 FollowUps:3
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I’ve heard the truckies on the UHF radio, exchanging abusive language about old farts in caravans.

I’ve read in caravan forums and letters to editors of Caravan Magazines about the inconsiderate, rude and aggressive behaviour of truckies on our roads.

Truckies communicate with each other on UHF Channel 40 (except on the Pacific Highway between Sydney and Brisbane, where Channel 29 is used). They also communicate with each other at truck stops and rest areas.

Caravanners communicate with each other at Caravan Parks, on internet forums, and some communicate on UHF Channel 18.

Most caravanners don’t communicate with truckies and most truckies don’;t communicate with caravanners.

Truckies are working in a high pressure transport industry, trying to maximize their efficiency by traveling at near the speed limit, right on the speed limit, or creeping just over the speed limit. Their workplace is on the road, and a major part of their profession is to tolerate traffic situations and share the road with others. Truckies have regulated work hours and can work up to 12 hours a day, with 7 hours of stationary rest.

Caravanners are on holidays, either touring or heading to a long stay vacation at their favourite caravan park. They are generally not in a hurry, and tend to travel considerably under the speed limit, and therefore, at a considerably slower speed than the trucks. They usually travel for 4 to 6 hours in a day and have 16 to 18 hours of stationary rest.

It is a pretty big conflict of interest on our roads, and this conflict is probably a major contributing factor in caravan crashes.

Every caravan tow vehicle (tug) driver has a responsibility to share the road with others, particularly in the area of co-operation with the truckies and helping them to share the road.


The first recommendation to caravan tug drivers is to acquire a UHF radio and use it to communicate with the truckies. If this can be achieved nationally and quickly, I believe the traditional bad language will diminish considerably, and may even disappear if the women in caravans can make their presence heard. The truckies will quickly learn of the benefits of communication with caravanners if the actions set out in this document are adopted by the caravanning road users.


A truck can have a maximum width of 2.5 metres (8 ft 3 inches.) Caravans can also be up to 2.5 metres, and tow vehicles are usually less than 2.0metres wide.

A truck passing a caravan, with a metre (about 3 ft 3 inches) between them will require a 6 metre (20 ft) wide road surface. Most rural two lane highways built in Australia up to the 1960’s had a maximum width of bitumen of 20 ft. Most rural main roads had a width of only 18ft. Many shire roads that were sealed in the 50’s and 60’s had a bitumen seal width of only 16ft. Many outback roads, when they were first sealed had a seal width of only 12 feet.

Many of these roads in Australia have not been widened, even though the maximum allowable width of vehicles increased from 2.4 metres to 2.5 metres in the mid 1970’s.. So, we must learn how to drive on these roads and share them with others, including the monster trucks.

Of course some major roads have been widened to 7 or 8 metres, and some of them now have sealed shoulders.


All caravanners will have experienced the buffeting wind that comes from a passing truck, either in the opposite direction, or when the truck is overtaking your caravan. The force of wind can be so strong that it affects the line of travel of your rig. Over-correcting in these situations can lead to loss of control, a collision with the truck, or jack-knifing, possibly ending in vehicle roll-over, on or off the road.

Understanding the dynamics of these instances, and knowing how to apply remedial action can avoid a disastrous event.


If the road is linemarked with only a centre line, the road may not be wide enough for the truck and car to pass without one vehicle or the other having to drive with left wheels on the shoulder. The caravan should slow down and very gradually move to the left so that the left wheels are off the bitumen, then, after the truck has passed, wait until there is a smooth path back on to the bitumen, and very gradually move back on. Any sharp change in direction or speed whilst the left wheels are off the bitumen can lead to instant loss of control. Do not brake hard in this situation because your right wheels will have more affective braking ability, resulting in the vehicle veering sharply back onto the road and into the path of the truck.

If there is no centre line, the bitumen road width is likely to be only 16 ft. (4.9m), or even 12 ft.(3.7m). Call the truckie on your UHF40 and tell him to “STAY ON” as you are going to slow down and pull off the road. That way you will not only gain appreciation from the truckie, but you will avoid being showered with rocks and gravel which you would get if the truck had to leave the bitumen.

If the road is linemarked (in accordance with Australian Standard AS1742) with a centre line and, edgelines on both sides, it will be wide enough for the truck and the caravan to pass without any wheels leaving the bitumen.

Apart from driving as far to the left as possible, the caravan towing driver must be prepared for the wind forces that will be exerted by the truck. It is a good idea, if, when you are travelling on an empty road (no other vehicles behind, in front or coming towards you) to practice, using your left side mirror, to drive so that the caravan wheels are just touching the edgeline. You can then establish a relationship between the left front of your vehicle, and the edgeline so that you can drive as close as possible to the edge of the road, without having the caravan wheels drop off the bitumen.

A bit of practice and you will be in the best position without having to glance across to the mirror.

So, when the front of the approaching semi-trailer is passing the tow vehicle, you will feel the buffeting of the bow wave of air that the truck is pushing at 100km/h. Your vehicle has wheels on each corner and the force of the wind should not affect the stability or direction of travel. When the bow wave hits the front of the caravan, as shown in Diagram 1, the force will have a severe effect on the stability of the caravan, The van is connected to your vehicle at the towball, which is a single pivot point, or fulcrum. The caravan’s wheels are in the middle of the van and therefore the centre of the axle(s) is another pivot point.

The force of the bow wave will push the front of the van towards the left side of the road, pivoting at the towball and the centre of the van’s axles. This subsequently creates a force at the front of the tow vehicle towards the truck. Added to this is the suction of air, back in towards the prime mover’s driving wheels, the “eddy”, or “vortex” behind the bow wave.

Image Could Not Be Found Image Could Not Be Found

Diagram 1 Diagram 2.

As the bow wave passes the van’s axles, ( Diagram 2.), the pressure on the side of the van will push the back of the van towards the edge of the road, with subsequent forces pushing the front of the van towards the truck, (aided again by the suction of the eddy) and the front of the tow vehicle towards the left.

If not counteracted by the driver, this could develop into an harmonic motion of opposite direction swaying, which can increase to a point of total loss of control, jack-knifing and then roll-over. End of holiday!

Holding the steering wheel firmly with both hands tightly, the left hand at “10 o’clock”, and the right hand at “2 o’clock”. Compensation for the changes in force contributable to the bow wave of the truck are by pressure only… not attempt to steer in the opposite direction to that of the force.

Remember a truck travelling towards you can be doing 100km/h and if you are doing 90km, the closing speed is 190km/hr. The truck will take only 0.2 seconds to pass you and you won’t have time to compensate for the change in forces anyway.

If your rig does start an harmonic motion, take your foot off the accelerator and slowly apply the brakes of the caravan. If you don’t have an electric brake controller with a manual over-ride, gently apply your footbrake, keep the tow vehicle pointing straight ahead and keep slowing until the rig is stable. Don’t try to accelerate away from the sway and don’t hit the brakes hard.


This can be a much more dangerous situation for the caravanner and I believe it may be a major contributory factor in the occurrence of jack-knifing and rollovers involving caravans. If you are travelling at 90km/h, and a 25m long B-Double is travelling at 100km/h, you will be subjected to the forces of truck generated winds for some 21 seconds, until the back end of the truck has passed the front of your vehicle. (Note: the times are measured from when the front of the 25m B-Double is 10 metres behind your 13m long rig, until the rear of the B-Double is 10m clear of the front of your tug.)

If you are on a two way road and you see the truck approaching from behind, call him up on Channel 40 and tell him that “As soon as you’ve pulled out, I’ll back off” . Do not back off until the whole of the truck is ”out” in an overtaking position. When the rear of the truck has cleared the front of your vehicle, flash your lights or call “You’re clear” on the radio. This will gain a lot of appreciation from the truckie as, if you can slow to 80km/h it will reduce the overtaking time by half, to 10.5 seconds. The truckie will thank you, either by calling on the radio, or by flashing his right turn indicator light, and then the left turn indicator light. At 80km/h, you will be in a better position to handle the forces of the truck’s bow wave, eddy and following turbulence.

Image Could Not Be Found Image Could Not Be Found

Diagram 3. Diagram 4.

As the front of the truck reaches the rear side of your van, the bow wave will push the back of the van towards the edge of the road (Figure 3) the front of the van will be pushed towards the truck, pivoting at the van’s axles. (This will be more pronounced with a single axle caravan).

The front of your tug will feel as though it is veering to the left. Do not try to turn the steering wheel to the right to compensate.

As with the approaching truck, keep your hands firmly at “ten and two” and concentrate on keeping a straight course. You will feel the pressure of the “force to the left” but your firm grip will compensate for the pressure. Next you will feel pressure to the right as the bow wave hits the front side of the van, pushing the A frame towards the left. The eddy, (or vortex) behind the bow wave, will tend to “suck” the rear of the van towards the truck, and this will exacerbate the forces. The front of your tug will feel as if it is veering to the right, towards the front of the truck.

Image Could Not Be Found Image Could Not Be Found

Diagram 5 Diagram 6.

You will next feel the bow wave hit the rear side of your tug (Diagram 5) and the eddy will draw the front side of the van towards the truck. The bow wave will then force the front of your tug to the left (Diagram 6) and the van will tend to be sucked towards the truck by the eddy. As the front of the truck passes the front of your tug, you will feel as though you are being sucked towards the bogey wheels of the truck. (Diagram 7.) This again is the force of the eddy behind the bow wave.

Finally, as the rear of the truck’s trailer passes, you will feel the buffeting of the “wake” and turbulence. This again will tend to pull the van towards the truck, but the forces will not be as great as they were in Diagrams 3 and 4.

Image Could Not Be Found Image Could Not Be Found

Diagram 7 Diadram 8.

The forces exerted by the winds of an overtaking truck can set up an harmonic motion which could end up in a situation as shown in the following photograph.


In this instance the momentum that could have contributed to the disaster would be exacerbated by the weight of the large outboard motor, spare wheel, and generator attached to the rear of the van and, the distance between this weight and the centre of the van’s axles.

The swaying in harmonic motion produces an inertia about the centre of the van’s axles. Inertia is measured by multiplying the weight (of the attachments) by the square of the distance between the attachments and the axles of the van. So, if the spare wheel was there when the caravan was purchased, and weighs 40kg and is mounted 3 metres to the rear of the centre of the axles, the inertia is 360kgm2. If the outboard motor weighs 50kg and the generator 25 kg and the mounting hardware 15kg., the combined weight is 130 kg. The Centre of this mass has probably moved to 3.2 metres from the centre of the axles and the resulting inertia is a massive 1331kgm2.

I have heard some say that they have added weight on the A frame to “balance” the rig and keep 10% of the GTM on the tow ball. For example, a folding boat trailer, jerry cans and boat fuel tanks. Well, this again is adding weight at some 3 to 4 metres away from the axle pivot point and this of course will add to the inertia when the van begins swaying.

To my knowledge, there has not been any scientific studies made to analyze the forces of deflected wind created by an overtaking truck, yet, the situation arises more frequently on our roads as old two-way highways are replaced by divided roads. How often do we hear that traffic on the freeway has come to a standstill because a car and caravan has jack-knifed?

I am not a Mechanical Engineer and I would be grateful if someone with more expertise in this area could provide an insight into dynamics of such forces in motion.

Rob Caldwell MITE(Life) MAITPM
Traffic Engineer.

With 10 years experience of towing a Bushtracker caravan around Australia.
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Reply By: Tellem Bugrem - Saturday, Mar 03, 2012 at 03:01

Saturday, Mar 03, 2012 at 03:01
Sorry Folks...............I'll retry the photoImage Could Not Be Found

AnswerID: 583886

Reply By: Andrew & Jen - Saturday, Mar 03, 2012 at 10:45

Saturday, Mar 03, 2012 at 10:45
Hullo Rob

Good post with plenty of excellent suggestions, especially the need to maintain your speed until the truck is fully out in the passing position. If you slow up beforehand, forcing the truck to also slow, it takes them longer to accelerate once they commence the passing manoeuvre - this markedly increases the overall time to complete overtaking. One additional suggestion, if I may, is to ask them to nominate when they want to pass, as most travel the road often and know where the safe passing opportunities with good sight distance are located.

After the bow wave effect, I think that the tendency to be drawn sideways into the side of the truck is more to do with the venturi effect than eddies. That is, the higher velocity air rushing between the 2 vehicles lowers the pressure relative to the other side of your vehicle, thus producing a lateral force towards the truck (same effect that produces lift by an aircraft wing). Ships passing closely, or travelling in parallel at the same speed (eg refueling) have the same issue - in the latter case they travel slightly splayed away from each other, if that makes sense.

The other thing that really bugs truck drivers is when a slower vehicle (often a tug/caravan combination) speeds up when they come to a section of road with an overtaking lane, thus thwarting the opportunity for the truck to pass and then drops back to the slower speed straight after. One has to wonder at the motives (and mentality) of such drivers.


(civil engineer in former life with 34 years experience in road construction / maintenance - and semi driver in uni vacations more years ago that I care to remember :-)

AnswerID: 583887

Reply By: Motley - Saturday, Mar 03, 2012 at 19:05

Saturday, Mar 03, 2012 at 19:05
A very good and timely post Rob.

When we see a truck coming up behind, I generally radio back and let the driver know that I know he's there and for him to pick the passing spot.

When he is right out on the passing lane, I apply the manual brake on the brake controller so that my rig is slowed by the brakes on the van, not the brakes on the vehicle. This seems to keep the rig straight while the "bow wave" hits us. It also reduces the time the truck spends passing.

It must work, because I've had many drivers radio back to thank us and on one occasion, at a stop further along the road, the driver actually paid for our drinks!

The radio can be great in helping all road users, trucks and caravans, to share the road safely.

Life's too short to drink bad wine.

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Follow Up By: Turist - Saturday, Mar 03, 2012 at 19:33

Saturday, Mar 03, 2012 at 19:33
With Bin 84 at $96.00 a bottle that was a costly shout.
Or have you changed your drinking habit :-)

"Do It While You Can"
Nobody is getting any younger.

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Reply By: Grumblebum & Dragon - Saturday, Mar 03, 2012 at 21:51

Saturday, Mar 03, 2012 at 21:51
Hi Rob - good post.

We always travel the back roads and tracks and therefore meet few truckies. Those that we do meet have always appreciated a call on the UHF...... "Southbound XYZ truck, overtake when you are ready - we will make space for you if required" or for approaching trucks, especially on narrow country roads I will call them up and suggest they stay 'up' and on the road -, we will pull off.

The advantages of the latter are (a) one happy trucker - loses no revs and stays on the tar (b) happy vanner not getting sprayed with gravel and dust, (c) Truckie see an example that not all caravanners ore stoopid duckheads A few moments delay in our trip is of no consequence but he is working, often in diffiocult circumstances.

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Reply By: Wherrol - Saturday, Mar 03, 2012 at 22:14

Saturday, Mar 03, 2012 at 22:14
Hi Rob,

Excellent post which we thoroughly concur.

We too radio back to the truckies and they are appreciative of our call.

As for the language, guess we are in their work space. They always call Allan "Mate" and I have been called "The Mrs; or love" on a few occassions.

Also wish that the wide load pilot vehicles would have a sign with the width of the following wide load on the roof of their vehicle, or would radio the caravans ahead like they do to trucks. Nothing scarier than a wide load, no room, and no idea how wide a load is coming at you.

Allan and Sharon

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Follow Up By: Rockgoc - Tuesday, Mar 13, 2012 at 00:59

Tuesday, Mar 13, 2012 at 00:59
As both a caravan tower AND a truckie in my former life, I would like to add my 2 cent's worth here. As far as not knowing what is coming or how wide it is etc, if you have a UHF radio, then use it....I always call up the pilot, and ask " We are the cruiser towing the wobbly (or caravan if you want to get technical)What have you got mate? Can you give us a width or length please?" and they always oblige and we know what to expect and whether to get right off the road or not. If the load is over 5 metres wide, then they should nearly always have a police escort leading the way. That way , you can get an idea of the size of the load coming.
Hope thiz hdelps. Cheers From Jan O with the bionic knees.
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Reply By: Theywent Thataway - Sunday, Mar 04, 2012 at 08:28

Sunday, Mar 04, 2012 at 08:28
Extremely well put. I have also driven semis and can relate to everything being said and agree with every bit of it. Just the other day we were following a semi who was wandering over the road. Concerned he may have been dosy Maz called him up on the radio to check on him. You should have heard the comments of thanks from him and other drivers for the concern. He was OK just reaching for stuff when there were no cars coming.

Can I also add that we have frequently passed Bushtrackers and when we try to call them up there is no response - so if you have a UHF at least have it on at all times as it can be an extremely useful tool.

the scruB ark...on The Way

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Reply By: Theywent Thataway - Sunday, Mar 04, 2012 at 18:53

Sunday, Mar 04, 2012 at 18:53
A big, but very good read!

A few extra points from a girls perspective.. particularly for the girls who are towing infrequently.

1) Girls.....Drive MORE!! At LEAST a few minutes each day you are travelling. Extend your comfort zone slowly. Fellas - that means LETTING them!

2) Get used to glancing at and utilising ALL of the mirrors when you are driving, We have 3...but only two are any good for my eyes to utilise. That way you'll KNOW whats behind you and nothing will take you by surprise by landing at your drivers side window when you least expect it. If your rear camera isnt always on, check quickly on bends in your mirrors for any traffic that might be wanting to pass, OR right on your tail.

3) To "fix" a good spot left of your lane to sit in whilst being overtaken by or passing ANYTHING, get a line of sight pre-arranged in combo with your passenger:-
a) check where your wheels are in the side mirrors (or when the passenger says you are close enough to the left edge) OR have the van wheels travelling right on the line. Try staying in that position for some distance. Then
b) "Spot" where different parts of the car appear on the line from your driving position. I.e...I found that the base of UHF antenna is just to the left of the line ahead. The top right corner of the bullbar is in a definite spot from the middle line.

4) Do the same for YOUR OWN overtaking position. I never imagined I would overtake anything whilst towing big trailers.....but now that I have had to more than a few times, and I know where the rig "sits" and how its likely to move I am much more confident.

5) Guys, get the gals to read this thread. At least they will have a clearer understanding of WHY the rig moves the way it does, regardless of who is driving. Then they'll expect the unexpected.

6) Know how USE YOU UHF!!!!!! Most oversize vehicles call for MILES when they are on the road. They state where they are, what direction they're travelling in and what size they are. Generally they are on 40, NSW north coast they use 29. They like to know that WE have acknowledged THEM. Dont expect your drivers to do the talking. Take the initiative, CALL the the things you are seeing or doing. LISTEN in - they let each other know whats happening on the roads in either direction around them. You'll learn how to call up others if you're a bit shy or unsure. It is one of the best resources you have on your rig. Ours is always on.

I had the most nerve wracking experience of my entire driving career during the second time towing the BT (I have experience with towing other trailers, riding big motor bikes, driving fast cars and small buses) on a narrow bridge with a passing truck. If I hadnt trusted my passenger (notes1952), been read up on towing large trailers, or had I have panicked.......well, I cant even begin to imagine how it would have ended. We now drive - towing a 10m/3.5T trailer - about 3,000km per week. This thread will make it even more enjoyable for me!

Maz. (MrsNotes1952)
the scruB ark...on The Way

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Reply By: Grumblebum & Dragon - Sunday, Mar 04, 2012 at 19:12

Sunday, Mar 04, 2012 at 19:12
Totally agree about the ladies driving more. They should be as competant as you towing in any conditions. One day they may have to while you croak in the passenger seat having a thrombie.

Same goes for the HF and UHF radio and sat phone as well as hitching and unhitching etc..... one day they may have to do it while under the stress of having a crook hubby.

And, you should both be competent and have up to date first aid certificates.

Have a safe one

AnswerID: 583893

Reply By: Uncle Dodgy - Tuesday, Mar 06, 2012 at 03:32

Tuesday, Mar 06, 2012 at 03:32
Congratulations Rob on a big job well done.
So well done in fact that I think it should be kept in postereity for the newbies in the Bog Bible. Have a chat to Boys Toy about its inclusion.
I too have both driven semi's and towed caravans, and found your notes to exactly describe the real life scenarios.
John & Sharyn
Takin' the long way home - Towing a Bushtracker

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Reply By: Deleted User - Tuesday, Mar 06, 2012 at 17:01

Tuesday, Mar 06, 2012 at 17:01
I caution road users including caravanners in believing all heavy vehicle drivers are professional in their approach to sharing the road and road safety.
I have had several near death experiences with overtaking trucks where an overtaking opportunity did not exist. Once they are level with you they will force you off the road if the need be.

It is foolish and dangerous to believe all truck drivers will do the right thing.

Believe me they are not concerned with your health and the road statistics would suggest that.

I don't trust and have no respect for any of them unless proven otherwise.

The word within the industry is the good drivers have moved to the resources sector and a lot of cowboys who are not good enough are now driving trucks.

If you believe the truckie will DO THE RIGHT THING you a delusional and I offer this posting in the hope a reader will sharpen his defensive driving skills as sharing the road with heavy vehicles requires a much more hightened awarenes than with other road users like automobiles motor bikes etc.

Be afraid...very very afraid.

I have a son in law in the industry.

Good post Rob.
Your post deals well with some of the dynamics of moving masses and proper control thereof.
To be forearmed is to be forewarned so always think ahead and develop a mental picture of posssible dangerous scenarios.

Defensive driving skills will perhaps save you from an adverse life changing event.

AnswerID: 583895

Reply By: Tellem Bugrem - Tuesday, Mar 06, 2012 at 18:33

Tuesday, Mar 06, 2012 at 18:33
Thanks for all your responses.

I have now modified the document to incorporate some of your suggestions, and to address issues you have raised. The next step is to post it in the Tips Section for BOG members and talk to Neil about putting it in the BOG Bible..

Andrew. Even if you ask the truckie to nominate when he wants to pass, you will still have to ensure that the truck is fully out when you start to back-off. (Using mirrors and/or rear view camera). Adding this task to the truckie, which involves holding the mike in one hand, whilst the other overtaking tasks (Visual, right blinker, checking rear view, possibly changing gears) might not be in the best interests of safety.

Whether it is called a venturi effect, vortex, vacuum or eddy doesn't really matter. The fact is it tends to "suck" the van towards the truck, after the bow wave has passed.

Pete. Yes! to using the manual caravan brake to back off will help to nullify the effect of the wind and minimize the risk of sway. Good.

John..... As with response to Andrew (above)

Allan & Sharon, Wide load escorts will call, eg. "4.5 approaching Spring Creek Bridge", if the wide load is going to encroach in the opposite direction lane. (You'll know it is coming towards you when you can't see the escort vehicle in your mirrors.)

Thanks Dave,, if all caravanners could adopt these practices, they would all be on 40 (29),...NOT on 18 or a private convoy channel, or, switched off!

Maz, Now that is a good suggestion, I'll pass it over to Liz to read!,

Ern 1943 (Good year!), Yes, of course there are some cowboys and law-breakers amongst truck drivers and I have seen plenty!. At least by calling them up you might get some idea of their attitude by their response, or non-response. This can at least serve as a warning and you can apply your defensive driving techniques. I did a Police Defensive Driving Couse in Canada in 1970 and the techniques have been part of my driving for 42 years.

Thanks again folks.

Safe Travels.............Rob
AnswerID: 583896

Follow Up By: Andrew & Jen - Tuesday, Mar 06, 2012 at 21:58

Tuesday, Mar 06, 2012 at 21:58
Hullo Rob

I think you might have mis-read what I wrote. I am agreeing with you that you don't start slowing down until after they are fully out.

And there are no additional tasks for them during overtaking.

A typical conversation might go something like this (abbreviated) - "G'day, I'm in the LC towing the van immediately in front of you. Happy to slow up when you are fully out ready to pass. If you know the road well, you might want to let me know when you are ready to go." "Thanks mate. There is a flat straight section in about 3 clicks. If nobody is coming, I will go then."

Then over the next little while before they pass, they often chat about where I'm going, where I was last night, their load and where they're going, etc. (Long distance truck driving can be a lonely job)

Finally a quick flick of the lights when they are far enough ahead, often followed by a quick thanks from them or the indicators L/R/L.

Ern1943, in my experience over 50 years of driving, there don't seem to be any greater percentage of anti-social truck drivers than there are in any other class of driver.

FollowupID: 854257

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