Slippery Road Vehicle Early Warning System: Method Augmentation


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National Surface Transportation Safety Center for Excellence


Two prior projects conducted by the Virginia Tech Transportation Institute (VTTI) for the Federal Highway Administration (FWHA) demonstrated that small but statistically significant differences in vehicle wheel rotational rates, attributed to tire microslip, can be used to quantify the changes in tire grip that occur when pavement conditions change due to road weather. The first project established proof-of-concept by demonstrating that tire microslip increased where the pavement was covered with liquid or frozen water and confirmed that OEM wheel sensors were of sufficient resolution to determine statistically different microslip rates at the driving and free-rolling wheels. The second project introduced the concept of a traction index (TI) and explored confounding factors, such as road incline and wind. Results showed that the “noise” that resulted from apparent vehicle acceleration and wind prevented accurate measurement of TI given the constraints of sensor resolution and other factors. For the current study, researchers hypothesized that instantaneous fuel consumption rate (IFCR) and engine throttle position, available from the vehicle network, might be used to correct the calculated TI to account for the confounds. The relationship between TI and IFCR and engine throttle position was analyzed using a variety of techniques. In the end, the research team was unable to demonstrate that basic TI calculated values could be corrected using vehicle dynamic data due to factors stemming from the unsuitability of the existing road friction dataset for the application intended. Over the time spanned by these three studies, some companies have begun to use microslip and other vehicle variables as a basis for dynamic assessment of road friction. Also, vehicle data, including that which might be used to assess road weather, are now available commercially. These data sources provide opportunities for future research on the safety and environmental benefits of real-time assessment and sharing of road weather information.



transportation safety, Connected vehicles, Naturalistic driving data, Tire friction