Trailer Safety

Many of today's vehicles are equipped with extra safety features built-in to aid the driver when towing a trailer or caravan. Some of these are for safety, and some are to assist the driver and make towing that little bit easier.

Towing Related Safety

However important the function may be, the vehicle will need to know that a trailer has been connected in order to access and operate these systems. This is achieved through the towing electrics, and provided that the correct wiring solution is used, all such functions will activate. If a by-pass system is used, it will not communicate.

Adaptive Suspension Icon
Adaptive air suspension is an electronically controlled air suspension system usually found on all four wheels, with a continuously adaptive damping system. Most vehicles fitted with Adaptive Suspension are able to vary their ride heights as well as the damping characteristics, and some can even detect the exact weight placed upon the rear of the vehicle whenever a trailer or caravan is coupled. Once the electrical towing plug is connected, a number of vehicles will adjust their height setting in order to keep the towing combination perfectly level and therefore more stable. They can also adjust the damping forces of the shock absorbers according the extra weight placed upon them. On vehicles with network systems, this feature will not function should inappropriate towing electrics be installed!
Adaptive Cruise Control Icon
Another adaptive system which can be altered by the detection of a trailer is the Cruise Control system. This new system utilizes radar lasers at the front of the vehicle to detect the exact distance of any vehicles in front. The driver is able to set the distance and/or speed that is appropriate and the vehicle will remain at these presets by constantly monitoring the distance and applying the brakes or throttle when needed. When towing, most systems will automatically set their cruise control to the maximum distance. This is to allow for the extra time needed to slow down a heavier towing combination. In the event of an emergency, some cruise control systems can also bring the vehicle to a complete standstill. On vehicles with network systems, this feature will not function should inappropriate towing electrics be installed!
Parking Assist
As the vehicle passes a parking space, the system ascertains the dimensions of the available space and of any obstacles. Once it has evaluated this sensory data, it automatically calculates the ideal parking manoeuvre. The driver then presses the button, which activates the parallel parking assistant, engages reverse gear, and uses the pedals to control the speed. The car will then steer itself into the available space. This system is automatically dis-engaged when a trailer is connected as the overall length of the vehicle has changed. On vehicles with network systems, this feature will not function should inappropriate towing electrics be installed!
Trailer Stability Icon
This is a system that is being incorporated into the brake electronics more and more. With the on-set of the requirement to have ESC* in every vehicle designated for distribution in Europe, T-Esp will become a rapidly growing feature. This system is designed to correct the "Snaking" effect that is usually caused by heavy gusts of wind, or a poorly loaded caravan or trailer. By using the vehicle's brakes and engine to control the speed and oscillation of the trailer the system stabilizes the towing vehicle and trailer combination. Once again, the vehicle needs to detect the presence of a trailer or caravan in order to determine how the on-board yaw sensors function. The Trailer Stability Program - T-Esp page will inform you about how this system works and also inform you about some of the benefits. On vehicles with network systems, this feature will not function should inappropriate towing electrics be installed!
Lane Change Icon
This feature is becoming more and more popular on today's vehicles. Most systems are equipped with a small camera/radar device fitted into each wing mirror. It is designed to alert drivers of the presence of on-coming vehicles entering the rear "blind spots", particularly when changing lanes. The system constantly monitors the adjacent right and left lanes and will provide an optical alert - with warning lights if a vehicle is detected in the blind spot zone. The system determines that the driver is performing a lane-change procedure through activation of the flasher indicator and will alert him/her accordingly. With a trailer connected, the system (Hella-Audi) becomes de-activated and the driver is alerted with a message display. This is because the towing vehicle is not currently able to recognize the additional length of a caravan which narrows down the monitored zone. Note: Hella are working on being able to incorporate the additional length needed when towing by increasing the rearward zone. On vehicles with network systems, this feature will not function should inappropriate towing electrics be installed! Therefore the use of any by-pass electrics will seriously compromise this system!
Automatic Handbrake Icon
Vehicles fitted with an Auto-hold handbrake will remain in place when the vehicle comes to a stop and the brake pedal is released. Most systems will wait until enough driving torque has been produced to pull away, before they release the brakes, allowing the vehicle to move off slowly without rolling backwards. This is particularly useful when towing as it makes hill starts easier and compensates for the extra weight of a trailer. Manufacturers may also call this system "Hill Start Assist". On vehicles with network systems, this feature will not function should inappropriate towing electrics be installed!

Along with all the safety features shown above, vehicle manufacturers are constantly investing more and more time and money into producing the next generation of systems to enhance the driving experience when towing a trailer or caravan. Some of these possible features are listed below:

Tyre Pressure Icon
Already in use on many vehicles, this system could be adapted to recognize the connection of the towing plug. The current systems monitor the tyre pressures of the vehicle and inform the driver if these drop below a preset lower level. Obviously the lower preset level would need to be different when towing a heavy trailer or caravan, as the vehicle needs to run higher tyre pressures. The vehicle could be coded by the towbar specialist to set the lower level warning to a higher pressure dependent on the size of the trailer or caravan. These levels may also be possibly set by the driver via the in-car multimedia centre present in most of today's vehicles. Another possibility is for the caravans tyre pressures to be monitored by the towing vehicle. This would require the caravan to be fitted with wheel monitors and to transmit a signal to the vehicle. The connection of the towing plug may "trigger" the vehicle to look for this signal, and therefore monitor the trailer or caravan's tyre pressures.
Trailer Alarm Icon
All manufacturers may produce their alarm systems to recognise the disconnection of the towing plug from the alarmed vehicle. This would require a can-bus module based wiring harness to be fitted to the vehicle and may also require the towbar specialist to perform a simple coding operation to activate the feature. On vehicles with network systems, this feature will not function should inappropriate towing electrics be installed!
* Electronic Stability Control

Trailer Stability

Over the last few years we have seen other safety features such as Brake Force Distribution, Side Impact Bars, Rear Passenger Airbags, Curtain Airbags and so on.

With such advances in vehicle technology, manufacturers have sought to develop a particular system which gives them the edge over their competitors. This is most apparent in on-board vehicle safety systems. In the 1980's, we saw ABS become a selling feature for one or two manufacturers, this is now common place on 99% of vehicles on our roads.

The latest safety feature which is fast becoming a primary safety feature on virtually all new vehicles is the Electronic Stability Programme (ESP). This comes in various guises depending on the manufacturer. For Example, BMW call this DSC (Dynamic Stability Control), Toyota use the term VSC (Vehicle Stability Control). Advances in vehicle technology have enabled a number of other safety features to incorporate a trailer. See 'Towing Safety Aids' for more information.

ESP -Icon
The electronic stability program (ESP) is a further enhancement to the Anti-Lock Braking System (ABS) and Traction Control System (TCS). The ESP is designed to detect a difference between the drivers control inputs and the actual response of the vehicle. When differences are detected, the system intervenes by providing braking forces to the appropriate wheels to correct the path of the vehicle. This automatic reaction is engineered for improved vehicle stability, particularly during severe cornering and on low-friction road surfaces, by helping to reduce over-steering and under-steering. To implement ESP functionality, sensors must be added to the ABS system. A steering wheel angle sensor is used to detect driver input, with a yaw rate sensor and a low-G sensor that measure the vehicles response. Some ESP systems include a connection to the powertrain controller of the vehicle to enable reductions in engine torque when required.
Trailer Stability Program Icon
When trailers or caravans start to sway dangerously, it is usually a result of the way of driving, speed, crosswinds, road condition and/or, a badly laden trailer or caravan. Caravans and horse box trailers present a special risk. When "snaking" occurs, many drivers display the wrong reaction and under stress, try to keep their tow vehicle and trailer on track by counter steering. This will only amplify the swaying effect and eventually result in an accident. The specific additional function of ESP, known as the Trailer Stability Program (TSP), recognizes swaying on the basis of the typical yaw rate in the tow vehicle. This allows for the right measures to be initiated at an early stage: the towing combination is slowed down to a non-critical speed by automatically braking all 4 wheels of the towing vehicle individually, whilst simultaneously reducing the engine speed and thus correcting the swaying movement. In most cases, providing the vehicle has been equipped a "Vehicle Specific Towbar Wiring Kit", the additional software in the ESP module is activated as soon as the electrical connection cable of the trailer is plugged into the towbar socket.

How do I know if TSP is working?

When the vehicle detects a swaying motion caused by a "Snakin" trailer, the TSP system will start to correct the movement. The driver will be informed via a flashing ESP light on the instrument display. Note: Some vehicles equipped with this system will perform a firm braking action. It is recommended that whenever the TSP is correcting the trailer that the steering wheel is kept in a straight position, in order for the towing combination to be controlled.

The information contained on this page is based on independent research into current vehicle stability systems and therefore does not constitute any legally binding documentation. This video was produced for educational reasons only.