6.2.4 Maintenance stage

where IRI refers to the international roughness index of the pavement at any time (m/km), cumulative ESAL refers to the cumulative axle load frequency after maintenance, and Initial IRI is initial international roughness index after road

The reflectivity of the pavement refers to the reflection ratio of the road surface to solar radiation. The reflectivity of the pavement affects the surrounding environment in various ways, thereby generating economic cost and environmental

Lawrence Laboratories in the United States released their reflectivity model in 2017. It takes urban building energy consumption as the evaluation object and evaluates the environmental impact of reflectivity from a city perspective [43]. Increasing the reflectivity of the pavement reduces the amount of heat absorbed by the pavement and increases the amount of heat that is reflected to the surrounding buildings. The former reduces the average temperature of the city and alleviates the urban heat island effect; the latter increases the temperature of nearby buildings, increases cooling costs, and reduces heating costs. In general, the former has a greater utility than the latter, so a highly reflective pavement can effectively alleviate the urban heat island effect. There are also many studies that assess the environmental impact of road reflectivity from a more macro perspective, considering the effect of reflectivity on radiative forcing. Radiative forcing is a measure of the extent to which a factor affects the earth-atmosphere system's energy ingress and egress energy balance. It is also an index that reflects the importance of this factor in the underlying climate change mechanism. There are many ways to calculate radi-

ative forcing, and the simplest one can be calculated using Eq. (10) [44]:

where ΔmCO<sup>2</sup> is the amount of change in CO2 emissions; C is a constant of CO2 emissions, using 255 kg/m<sup>2</sup> as the reference value; A is pavement area; and Δα is the variation of pavement reflectivity. This model considers only the effect of reflectivity changes on CO2 emissions, so it is the simplification model without consider-

In addition, there is another method for calculating the radiative forcing consid-

The left side of this formula indicates a change in the reflectance per unit area of

method is relatively simple, it does not need to consider the localization of multiple parameters. It has been used by many studies and indirectly proves that it has

In addition to the above factors, cement and asphalt binders will also undergo changes in properties under environmental influences, which will have an impact on the environment. During the firing of cement, limestone releases a large

0.01, and the right side indicates the CO2 emissions caused by the change in reflectance over time t. RF refers to the change in radiative forcing due to changes

in surface reflectance, with a reference value of 1.12–2.14 W/m<sup>2</sup>

<sup>0</sup>:<sup>217</sup> � <sup>t</sup> � <sup>44</sup>:78e�t=172:<sup>9</sup> � <sup>6</sup>:26e�t=18:<sup>51</sup> � <sup>0</sup>:22e�t=1:<sup>186</sup> <sup>þ</sup> <sup>51</sup>:<sup>26</sup> ½ � kgCO<sup>2</sup> (11)

ΔmCO<sup>2</sup> ¼ 100 � C � A � Δα (10)

. Because this

maintenance.

impact.

6.2.3.2 Reflectivity impact model

Transportation Systems Analysis and Assessment

ing time and environment.

certain reliability.

102

6.2.3.3 Impact from other factors

ering time variation, as shown in Eq. (11) [45]:

<sup>þ</sup>0:01<sup>α</sup> <sup>¼</sup> <sup>1</sup>:<sup>087</sup> � RF � <sup>t</sup>

This stage mainly calculates the environmental impact of various maintenance strategies during the long-term use of the pavement. The main environmental impacts at this stage are divided into direct and indirect effects. Direct impacts include the environmental impacts of material production and maintenance construction required for maintenance activities, which are similar to the material production and construction phases. Indirect impact refers to traffic delays caused by maintenance activities, which creates an additional environmental burden. The maintenance of the pavement must partially or completely block traffic for a period of time, causing the vehicle to slow down or bypass, which will result in an increase in fuel consumption of the vehicle.
