Jack-knifing occurs when the trailer slides forward and swings out, facing a different direction than the truck. It includes several risks for oncoming traffic, the driver and the goods.
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Volvo Trucks boosts safety on slippery winter roads

For trucks with trailers, slippery winter roads and downhill gradients represent a tough challenge for even the most skilled of drivers. There is always the risk of the rig becoming unstable and, in the worst-case scenario, starting to jack-knife. Volvo Trucks has now developed a solution that significantly improves safety.

 

“Even if the truck driver ultimately manages to control the situation, it can be extremely unpleasant both for oncoming road users and the truck driver, if a rig suddenly veers off its intended course on a downhill gradient,” says Mats Sabelström, brake specialist.

In order to minimise the risk of this type of situation and potential accidents, a system known as Stretch Brake has been developed that automatically retards the trailer and straightens up the rig on slippery downhill stretches.

“About 15 per cent of the total of 30,000 serious road accidents in Europe every year involves trucks, in a slightly declining trend. With effective brakes, stability systems and collision warning systems we are already helping drivers avoid risky situations in difficult conditions. Stretch Brake is yet another important part of our long-term drive to increase traffic safety and minimise the number of accidents involving trucks,” says Carl Johan Almqvist, Traffic and Product Safety Director.

Stretch Brake is a complement to the rig’s electronic stability program (ESP) – yet another system that Volvo Trucks was the first truck maker in the world to introduce. While ESP is at its most effective at higher speeds, Stretch Brake is only operational at speeds below 40 km/h. Both systems contribute to better stability and easier steering.

“One might call Stretch Brake a kind of low-speed ESP. As the rig approaches a downhill slope, the driver manually activates the system. When the driver then releases the accelerator, the brakes on the trailer are automatically applied in a pulsated mode all the way down the hill until the gradient levels out and speed can once again be increased,” relates Mats Sabelström.

Stretch Brake was introduced in 2012 on Volvo FH trucks pulling drawbar trailers and in 2013 on Volvo FM trucks pulling drawbar trailers. In 2014 it will also become available for Volvo FH and FM semi-trailer rigs.

According to the Volvo Trucks Accident Research Team, specialising in studying traffic safety, about 60 or so of the truck accidents that occurred in Sweden alone last year could have been avoided with Stretch Brake.

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