• Development of Friction Performance Models

    NCDOT Research Project Number: 2022-05

 Executive Summary

  • NCDOT manages the annual Highway Safety Improvement Program to address crashes in the followi​ng emphasis areas: lane departure, frontal impact/intersection, and pedestrian and bicycle crashes in an effor​t to reduce crashes by the installation of safety improvement countermeasures at locations with patterns of correctable crashes.

    Lane departure crash patterns can be identified in various ways with one of the methodologies being an increased frequency of lane departure crashes and/or crash rates during wet road conditions.  Lane departure crashes and crash rates may increase when the surface is wet because skid resistance can be affected and reduced under these conditions. 

    Recent studies have shown that friction and, more notably macrotexture, are negatively affected when the pavements are newly overlaid, but did not provide the NCDOT with a pavement friction and macrotexture performance model or performance thresholds. 

    This research study has used a combination of field experiments, laboratory experiments, and statistical analysis to achieve three objectives; 1) characterize friction and texture performance models for North Carolina roadways, 2) propose friction and texture performance thresholds, and 3) identify asphalt mixture compositional factors that affect the as-constructed macrotexture and friction. 


                              Friction concept schematic

    The objectives were met using a combination of field and laboratory friction and texture experiments. The performance models developed in this research were shown to accurately predict in-service friction and texture and were validated using completely independent measurements. To define thresholds, pavement segments were grouped according to their available friction or texture and then the relationship between the aggregated crash rates and texture/friction were used to identify values where crash rates showed a marked increase. 

    On the basis of this analysis, the research team recommends the following investigatory and intervention thresholds: macrotexture investigatory level: 0.80 mm, macrotexture intervention level: 0.6 mm, friction investigatory level: 0.57 for non-interchanges and 0.65 for interchanges, and friction intervention level (specific to Moventor BV-11 equipment at 60-mph): 0.43 for non-interchanges and 0.49 for interchanges. These thresholds are specific for the devices used; in the case of texture the AMES AccuTexture 100 and for friction the Moventor BV-11 at 60-mph

    The sites in this research were primarily high speed, controlled access roadways and so these recommendations are most applicable to similar types of roadways. Data from the North Carolina highway network was combined with these threshold values and predictions from the friction and texture performance models to evaluate the benefit-cost implications from deploying a set of maintenance and rehabilitation strategies to address friction and texture problems. 

    While the precise cost implications varied by the maintenance scenario evaluated or the interest rate used, all the combinations showed a benefit-cost ratio greater than one. 

B. Shane Underwood
B. Shane Underwood; Cassie A. Castorena
Shawn Troy
Mustan Kadibhai, PE, CPM
NC State University

 Related Documents

 Report Period

  • August 1, 2021 - July 31, 2023


  • Complete


  • Pavement, Materials and Maintenance

 Sub Category

  • Pavement Performance

 Related Links

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