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Estimate Consumed Life In most cases, the unexpected heavy vehicles will not be anticipated by the local highway agency at the time of design and construction. One parameter that can be estimated is the percent of the original design life is consumed by the additional heavy vehicles. This is based on the original design ESALs and the ESALs contributed by the additional heavy vehicles. L /ooife = ESALSWith — ESALSWithout ESALsDesign Estimate Performance Degradation (6) For the estimation of pavement degradation in terms of Pavement Condition Index, the tool uses the methodology used by MnDOT's Pavement Management Unit in a report by Lukanen and Han (23). The pavement performance prediction models in that report allow for prediction of pavement condition indices based on the previous three condition surveys. In cases where three previous surveys are not available, default values for the model coefficients are recommended. P PSR = P — OP • e O (AGE 7 o where: PSR = predicted pavement performance index, Po = initial performance index value, AP,p,p = regression coefficients, AGE = age of pavement structure since last reconstruction. The example below shows how this process is conducted. Since the year of last reconstruction is an integer, and the dates that the pavement condition surveys were completed most often have specific days and months associated with them, it is assumed that for age computation purposes the date of construction is the end of the month of July in the year provided. In this example, the pavement was last reconstructed in 1999. Table 6. Example PCI Prediction Data. PCI Date PCI Age 5/8/2001 98 1.77 4/13/2009 86 9.70 7/24/2012 64 12.98 20