Overtaking and being overtaken.


This video helps explain about what to do at a roundabout when following a truck.



One of the biggest complaints made by truck drivers is that RV’s & caravanners try and help by slowing down when they are approaching an overtaking lane or opportunity. 

They mistakenly believe that when they slow it makes it easier for the truck to overtake.  In fact it makes it much harder for the truck driver.  

By slowing down before the overtaking lane, the truck driver behind you, must also slow, therefore losing momentum and the engine may also slow to below its most powerful revs. It will then take longer to build up speed to overtake and it may run out of double lanes before it has completed the overtaking manoeuvre leaving the caravan or RV with nowhere to go when their lane ends.      

Remember, many trucks are speed limited so cannot overtake at high speed.     

The best way to help is maintain your speed until the truck is beside you in the other ‘overtaking’ lane, not behind you, and then ease off your accelerator to gently slow your rig. Keep your van straight and avoid heavy breaking that may cause the van to sway.     

The rush of air from the passing truck can also cause caravan sway, so be prepared.  See below for more information on air flow and how it impacts overtaking trucks.

This will help the truck get past faster, safer and without losing valuable engine power or speed, especially as many overtaking lanes are on inclines where trucks and caravans struggle to maintain their speed.     

Once again, communicate with the truck driver and let them know what you intend to do BEFORE you do it.


Be sure to keep an eye on the rear view mirror and do a head check of your blind spot to ensure there are no other vehicles also wanting to overtake you at the same time tucked in behind the truck.    

It is better to have them overtake and get away from you than have them constantly behind you getting agitated. 

Agitated drivers have been known to overtake when it is not safe out of pure frustration - endangering the lives of themselves, you and the other road users.  

There also may be that driver who tries to out run you before the end of the overtaking lane, so indicate early that you are running out of your lane and are moving back into the other lane when safe. Let them know your intentions early.     

Other drivers will appreciate it and you will often get a “thank you” over the radio. 

You will feel good knowing you have been Truck Friendly and have helped and brightened someone day.     


Be sure to give anyone overtaking you plenty of space and move as far left in your lane as you can safely. 

Stay in your lane and do not move off your lane onto the shoulder due to rocks, and unsafe road surfaces. All drivers do not like having their windscreen smashed by the driver in front showering them with loose rocks from the side of the road. Keep your van straight and avoid heavy breaking that may cause the van to sway.  

Gently back off the accelerator once the overtaking vehicle is beside you to help them get passed as quickly and safely as possible.     

Communication prior to the overtaking is always good and let’s everyone know what is happening.      

When you see the truck behind, let the truck driver know that you are aware they are there and you are ready to help when needed. They usually appreciate the offer to help and will let you know when they are coming around.   

DO NOT USE YOUR INDICATOR TO TELL THE OTHER DRIVER THAT IT IS SAFE TO OVERTAKE. This is illegal and dangerous as you do not know the skill and experience of the other driver, you do not know the acceleration of the following vehicle and you may pressure them to do something that is not safe for them and putting all lives at risk.

Use your radio to talk to them is the best advice.

Often they are familiar with the road and they may be comfortable to stay behind you as they know a passing lane or small town may be coming up where it is safer to overtake or for you to pull over.  Keep an eye on the rear view mirror and if you see a line of cars behind you remember it is safer to let them pass than have agitated drivers being held up.   

When it is safe, pull off the road and let them all pass, especially if you are passing through a small town or village where there is plenty of safe places to pull over at lower than highway speeds. 

This video explains about being overtaken by a truck.


Check out the 3-2-1- Green reflectors article on how to find a safe place to pullover.   https://truckfriendly.com.au/travelling-in-convoy


Ask yourself the questions:- 

  • "Do you really need to overtake the vehicle in front? Why do you need to overtake?"
  • "Are you or the vehicle in front likely to stop a little further up the road?"
  • "Are you due for a break and stop for a coffee instead?"
  • "Is there likely to be an overtaking lane or safer place to overtake up ahead?"
  • "Are you leaving enough space for other vehicles behind to leap frog around your vehicle and the one in front and therefore do not need to overtake?"
  • "Have you communicated your intentions with the truck in front?" They may say they are stopping ahead etc.

Always try and ensure the vehicle in front is aware that you are there and intend to, or are overtaking. Many truck drivers will assist by letting you know when the road ahead is clear and safe to pass.

Make sure there is enough room for you and the caravan or RV to overtake safely. 

Accelerate smoothly and watch out for caravan sway during and at the end of the overtaking manoeuvre.

If passing, or being passed by a large truck there will be a suction effect behind the truck and an air wall in front of the truck. This suction and then push effect can cause the caravan to be sucked into the truck at the start and then pushed away from the truck when completing the overtake. 

An unstable or badly loaded caravan can start to sway and it can quickly escalate out of control, especially at speed.  Check out the link to the Caravan Sway video abo

Many caravans and tow vehicles have been caught on trucks dash cams swaying and eventually rolling from this suction and push effect of the air around a large vehicle travelling at speed.

Give plenty of room before you pull back into the left lane and remember the length of your caravan needs to be allowed for plus a safety buffer for the vehicle you have just overtaken.

All movements should be smooth to help avoid caravan sway.

Have a look at this video on overtaking a truck. 


Other drivers will appreciate your professionalism and everyone will have a better journey by being Truck Friendly.





Click on this link below or keep reading for two explinations on what actually happens when caravans and trucks pass eachother on the highways.




Have you heard the truckies on the UHF radio, exchanging abusive language about old farts in caravans? 


Have you 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 when they are on the road. 


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 (ie Channel 40 and 29…not 18). If this can be achieved nationally and quickly, the traditional bad language could 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 6.1mmetres, or 20 feet. Most rural main roads had a width of only 5.5m (18ft). Many shire roads that were sealed in the 50’s and 60’s had a bitumen seal width of only 4.9m (16ft).  Many outback roads, when they were first sealed had a seal width of only 3.66m (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. Cabover or flat fronted trucks produce a stronger “bow wave” of wind than trucks with long bonnets over the engine and some trucks may have more than one “bow wave”, depending on their configuration and load. For example, a low loader with rear ramps in their upright position and no load, can produce a “bow wave” from the ramps, and likewise, a road train with a high load on the rear trailer. 


The force of wind can be so strong that it affects the line of travel of your rig. Overcorrecting in these situations can lead to loss of control, a collision with the truck, or jackknifing, 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, (ie, no edge lines), 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 effective 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 would happen 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, 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. 


As the bow wave passes the van’s axles,  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…..do 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 the truck is a 55m long, 4 trailer road train, as you would encounter on the Great Northern Highway (WA) or the Stuart Highway (SA & NT), it will take 32 seconds to pass. 


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. 


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 , and 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. 

You will next feel the bow wave hit the rear side of your tug  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  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.  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.


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 example of a caravan sway rollover  on the Pacific Highway near Coolongolook where the caravan had a generator, spare wheel and outboard motor attached to the rear of the caravan. 


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. 





Occasionally, there may be a need for vehicle towing a caravan, to overtake a truck. This manoeuvre has the potential for an even more disastrous result, simply because the caravan rig must travel faster than the truck. The wind forces are a mirror image of the overtaking truck situation described before. 


Event No. 1. Tug enters vortex and is drawn towards the truck. 


Event No. 2. Tug hits bow wave with forces to the right, and front of caravan is in vortex, drawing towards the truck, setting up the harmonic motion. 


Event No.3.  Bow wave hits front of caravan and rear of caravan is drawn into vortex, exacerbating the harmonic motion. 

Event No. 4. Rear of caravan hit by bow wave forcing it violently to the right. 


 Event No. 5. Caravan releases from bow wave, swinging back towards the front of the truck. 


 Event No. 6. Harmonic motion swings van from side to side. The black skidmarks are from the car braking hard. There are no caravan braking skidmarks, only yaw marks as the caravan swings back to the left. Driver has totally lost control. 

   Event No. 7. Tow vehicle braking skid marks turn to yaw marks. Left wheel of caravan starts yaw mark. Car broadsides off road, left wheels drop down embankment, digging in and causing vehicle to roll, caravan roll follows. 


On a flat, straight stretch of outback highway, (possibly with a speed limit of 110km/h), the truck is probably travelling at 100km/h. It is estimated that the caravan rig is about 10.5 metres in overall length. It took the rig 2 seconds to pass a reference point on the truck. (ie, 5.25 m/sec faster than the truck). The calculations show that the caravan rig was travelling at 119km/h. as it passed the front of the truck. If the truck was doing 95km/h, the caravan rig was doing 114km/h. 


The video recording by the truck driver.

In the facebook page, there were several responses, some of which said that the driver should have accelerated to stop the sway. Such action in this case (the rig was already travelling at high speed), would have increased the pitch of the harmonic motion and the result would have been more catastrophic.  


In reality there were two ways to avoid this crash:- 1.  Don’t try to overtake a truck at high speed….stop and have a cup of tea! and, 2.  If you must attempt to overtake, make sure you have electric brakes fitted to the caravan, with a manual override – do not apply car brakes if swaying commences. Activate the caravan brakes manually, and steer your car straight ahead until the rig has stabilized. By this time the truck will have most likely continued on, and you will need to stop and have a cup of tea! 


On multi lane roads, caravan rigs will often have to pass trucks and, of course, the same wind forces will be experienced. On these roads the lanes may be a little wider and the shoulders are usually sealed. This gives the caravanner the opportunity to pass with a larger gap between the truck and the caravan, thereby reducing the impact of the wind forces. 




A most graphic display of wind force setting up increasing harmonic  motion, or oscillations, was the spectacular destruction of the Tacoma Narrows bridge in Washington State, USA in 1940. There are many photos and films of this event and it is certainly worth a Google – Just type in “Tacoma” and have a look. The contributory factors were given as :- 


1.  Random Turbulance 2.  Periodic vortex shedding and, 3.  Aerodynamic instability. 


Perhaps we have a correlation here, with the random turbulence being the bow wave, and eddy (or vortex behind the bow wave) and the periodic vortex shedding being the  effect of the wind forces on the side of the van. The aerodynamic instability, or what I have referred to as harmonic motion, is probably related to the fact that the towing vehicle has 4 wheels, each near a corner of the vehicle, and  the single pivot point  connection to a van that has the wheels in the centre of the vehicle. 


Perhaps caravan manufacturers should be looking at building a van that has a front and rear axle, like the dog trailers behind tip trucks. 


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?  


Whilst truckies must have a special heavy vehicle driver’s licence and must undertake mandatory training in handling their rigs, car drivers who are towing caravans have not had any training in handling their rig, unless they have attended a towing course of their own choosing and expense. Most simply assume that as they are licenced to drive a car, they are capable of towing a caravan. To my knowledge, towing courses do not address the issue of wind forces from trucks and the subsequent potential of harmonic motion causing loss of control. 


There are several towing guides, brochures and booklets published by road authorities, motoring organizations, insurance companies, and caravan magazines, very few of which address the issue of wind forces from trucks. 


There is a clear need across all levels of Government, the media, and all organizations associated with caravanning, to provide education, training and re-training of drivers who are towing caravans and camper trailers. There has been many fatalities, serious injuries and family trauma resulting from ignorance and lack of knowledge in caravans  and trucks sharing the road. 


Rob Caldwell    MITE(Life)   MAITPM Traffic Engineer.                                                       August  2010 (Updated April, 2014) 




Why the wobbles, when being overtaken or overtaking a truck?