During February 2025, Finnish Meteorological Institute, in co-operation between Nokian Heavy Tyres and University of Oulu, conducted heavy vehicles braking distance measurements on icy road conditions in the city of Pudasjärvi. These measurements will be used to improve the services being developed in the Safetrucks projects.
Understanding the braking distance of a vehicle is crucial, especially during winter when icy and snowy conditions can significantly impact driving safety. Road friction (resistance between a vehicle’s tires and the road surface) plays a vital role in determining how quickly a vehicle can come to a stop when the brakes are applied. In order to measure the friction and braking distance multiple measuring devices were used during the campaign.
Testing was led by Nokian Heavy Tyres. Each vehicle was equipped with an IMU(inertial mass unit) and GPS- sensors in order to measure the braking distance of the vehicle. In addition to automatic methods, the distance was also measured manually.
After each brake test the road friction was measured with optical sensors and with a skiddometer by Finnish Meteorological Institute and the University of Oulu.
About the road friction sensors:
Optical friction sensors measure the reflection of light from the road surface. A light is emitted onto the road in different wavelengths, and the sensor measures the amount of light reflected back. The presence of water, ice, or snow affects the reflection, allowing the sensor to determine the road’s condition and estimate the friction of the road from the reflected light.
Unlike optical sensors, a skiddometer measures the friction between a test wheel and the road surface. In some conditions this method can provide more accurate measurements compared to optical sensors because a tire can penetrate thin layers of ice or snow on the road. A skiddometer records friction values continuously while braking on the wheel testing the road surface along the length of the road.
The event was supported by Lappia Vocational College and VR Transpoint (recently known as Kuljettava Oy) with their trucks. Lappia Vocational College also had students participating in the event to learn the importance of driving distance in bad weather conditions.
More information
Dr. Timo Sukuvaara, Finnish Meteorological Institute, timo.sukuvaara@fmi.fi
or from the website: https://safetrucks.fmi.fi/
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