Definitions

Thawing Index (TI)
TI = (Average Daily Temperature - Reference Temperature)

Reference Temperature
Varies from 29 degrees F on February 1 to 24 degrees F on March 15

Cumulative Thawing Index
Summation of the Daily Thawing Indices

Criteria

Based on observations of pavement deflection, frost depth and air temperature at the Mn/ROAD site, thawing reaches a critical state at a cumulative thawing index of about 25 DegFDays. The criteria used to begin road restrictions is a cumulative thawing index greater than 25 DegFDays and a weather forecast that predicts further increases in the thawing index.

References

The above criteria are based on findings contained in the publication by Van Deusen, Schrader, Worel and Bullock,1998, "Springtime Thaw Weakening and Load Restrictions in Minnesota, Transportation Research Record 1615" presented at the 77th Annual Meeting of the Transportation Research Board, Washington, DC.