Large-scale implementation of floating car data monitoring road friction

In Sweden today, friction measurements are performed manually, often using methods generating spot-wise measurements. Because the low numbers of measurements provided by these methods are insufficient to follow up on the friction requirements set by the Swedish Transport Administration, the Administration has initiated the Digital Winter project. In Digital Winter, floating car data (FCD) are utilised for road friction estimation. The focus in this investigation is on coverage, and on whether the FCD detects harsh weather conditions with decreasing road friction. Two different methods-one continuous and one slip-based-are implemented in this investigation. Furthermore, different approaches on how to build the vehicle fleet to collect the FCD have been applied using different combinations of commercial and private vehicles. The results showed that both methods detect low-friction events, and for roads with high annual average daily traffic (AADT), the data collection using slip-based methods and larger fleets gives more data points than for smaller fleets using continuous methods, and the reverse is true for lower AADT. The results showed differences between the two fleets in terms of coverage for the weekly and daily distributions, but overall, the method of using FCD for road friction estimation seems promising for the follow-up of winter road maintenance.