LowEmissionAsphalt-136pg-WhitePaper-May2023

P a g e | 91 Pavement smoothness can be quantified using international roughness index (IRI) 192 and is used by SDOTs as a performance measure in conjunction with other pavement structure-related performance measurements, such as cracking, or raveling etcetera to assess pavement condition ratings. Table 9 – International Roughness Index Ratings (in/mile) Very Good Good Fair Poor Very Poor FHWA <60 61-95 96-120 121-170 >170 Source: FHWA An IRI value greater than 121 in/mile is considered poor ride quality by FHWA. FHWA sets 120 in/mi for pavements going from the “fair” pavement condition to “ poor ” pavement condition. The ages of AC and PCC pavements at which their smoothness reaches 120 in/mile are similar according to a study focused on pavement smoothness and the use of IRI criterion for determining performance. 193 So, can IRI analysis 194 also be used to assess potential emissions savings (Table 10) ? Table 10 – International Roughness Index (IRI) to Gas Emissions (AC & PCC) (g/mile) Good Poor Very Poor R 2 CO 2 505.23 575.29 607.96 0.51 NOx 47.77 53.12 56.71 0.27 Source: University of Texas at El Paso Yes. T he potential emissions savings by improving IRI from “poor” to “good” ride quality condition (~50 IRI improvement) ranged ~12% for CO 2 and ~12% for NOx. The acceptable correlation or R-squared (R 2 ) for CO 2 is promising. The lower R 2 for NOx is a function of the far less amount of nitrogen available to measure against all 192 international roughness index is the roughness index most commonly obtained from measured longitudinal road profiles. It is calculated using a quarter-car vehicle math model, whose response is accumulated to yield a roughness index with units of slope (in/mi, m/km, etc.). 193 Robbins M and Tran N, Determining Initial Service Life for LCCA Using Comparable IRI as One of the Criteria , National Center for Asphalt Technology (NCAT), Auburn University, August 2019. 194 Gonzalez Calvo OD, Quantification of the impact of Asphalt Pavement Conditions on Gas Emissions , University of Texas at El Paso (UTEP), January 2017.