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(mm/m) <br />20 <br />18 <br />16 <br />14 <br />12 <br />10 <br />F, t Older <br />Pavement <br />6 New <br />4 1 Airports Pavement <br />Highways Maintained <br />2 ' <br />Unpaved <br />o 1 — Road <br />Damaged <br />Pavement <br />Figure 7 - IRI Scale Definitions <br />Normal Speed <br />20 mph <br />30 mph <br />40 mph <br />50 mph <br />Rough <br />Unpaved <br />Road 60 mph <br />In order to align with the PCI scale so that a blended condition score can be formed, the IRI value is <br />converted to a 0 to 100 score and reported as the Ride Index (RI) as follows: <br />RI = (11— 3.5 x In(IRI)) x 10 <br />In(IRI) is the natural logarithm of IRI. <br />For some context, a newer street would generally have an RI above 85, while one in need of an overlay <br />would be in the range of 40 to 70. Roadways in poor condition typically have RI values below 40 but can <br />achieve higher blended scores if the distresses causing the low RI score are not the result of structural <br />failure or another severe cause. For example, hastened construction can result in a pavement surface <br />with less than desirable smoothness, which would translate to a low RI value. But since the <br />distress/imperfection is not due to severe failures within the pavement structure, the blended PCI value <br />may not suffer greatly. <br />Structural Index — Per the wishes of the City, the roadways were not subjected to conventional <br />structural testing. Instead, the relationship between the PCI and the amount of load -associated <br />structural distresses was analyzed, and each pavement section was determined to have a Weak, <br />Moderate, or Strong strength rating. The strength rating then translated to a Structural Index (30, 60, or <br />90 for weak, moderate, and strong respectively). It is important to note that these SI values were not <br />used in determining the overall pavement condition score, as they were not calculated from true <br />structural testing. These SI values were simply used to classify the pavement strength and aid in <br />selecting appropriate rehabilitation strategies. <br />Pavement Condition Index (PCI) — Following the field surveys, the condition data was imported to Lucity <br />for calculating the overall PCI. The PCI for each network was calculated using the following weighing <br />factors: <br />PCI = 67% SDI + 33% RI <br />IMS Pavement Management Report Louisville, CO 2022 Page 112 <br />