New anti-jack-knife technology from Volvo Trucks

Volvo Trucks has now developed a solution to this problem that contributes significantly to the safety of heavy vehicles hauling trailers in challenging driving and weather conditions.

“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, a brake systems specialist with Volvo Trucks.

In order to minimise the risk of situations like this developing and the possibility of ensuing accidents, Volvo Trucks has developed a system known as Stretch Brake that automatically retards the trailer and straightens up the rig on slippery downhill stretches.

According to the Volvo Trucks Accident Research Team, about 60 or so of the truck accidents that occurred in Sweden alone last year could have been avoided with Stretch Brake [1].

“About 15 percent of the total of 30,000 serious road accidents in Europe every year involve trucks, in a slightly declining trend [2]," says Carl Johan Almqvist, traffic and product safety director at Volvo Trucks.

"With effective brakes, stability systems and collision warning systems we are already helping drivers avoid risky situations in difficult conditions,” he adds. “Stretch Brake is yet another important part of our long-term drive to increase traffic safety and minimise the number of accidents involving trucks.”

Stretch Brake is a complement to the rig’s electronic stability program (ESP). While ESP is at its most effective at higher speeds, Stretch Brake is only operational at speeds below 40km/h. Both systems contribute to better stability and easier steering. 

“One might call Stretch Brake a kind of low-speed ESP, Mats Sabelström explains. "As the rig approaches a downhill slope, the driver manually activates the system, and when he 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.”

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.

“Drivers who have tested Stretch Brake came away very impressed with the system,” says Carl Johan Almqvist. “As we are now also introducing the system on tractor-semi-trailer rigs, more drivers will be able to safely and easily negotiate difficult downhill gradients.”

Stretch Brake facts at-a-glance:
•Increases safety on downhill gradients, especially on slippery roads and in curves.
•Applies the drawbar brakes in a pulsating mode.
•Straightens the rig, makes steering easier and reduces the risk of jack-knifing.
•Operational at speeds below 40km/h.
•Introduced in 2012 on Volvo FH trucks and in 2013 on Volvo FM trucks. In 2014 it will also become available on tractor/semi-trailer rigs.

To see Stretch Brake in action here.

References
[1] Source: STRADA 2012, STRADA is a national (Swedish) information system collecting data of injuries and accidents in the entire road transport system. STRADA is based on information from the police as well as hospitals.

[2] Source: CARE 2011, CARE is the European centralised database on road accidents which result in death or injury across the EU.