6. Integrated life cycle economic and environmental impact method

As mentioned above, the calculation process of life cycle cost analysis is to divide the total cost into two categories according to the undertaker, owner cost and user cost, and further subdivide and calculate these two types of costs. The road life cycle inventory analysis process, in order of time and space, calculates the environmental impact of the whole life cycle; however, further discussion of each part will find a lot of similarities between the objects evaluated by the two as shown in Figure 3.

For example, the "raw material acquisition" and "construction" stage in LCI and the "construction" part in LCCA are evaluated on the pavement materials and construction process. The "maintenance" stage in LCI includes both the "maintenance" and "management" processes in LCCA. It refers to the maintenance work performed by the owner to maintain its structure and function after the pavement is put into use. It also contains the user's cost of evaluation, which is the additional cost and impact of the maintenance of the user. Therefore, there is a great deal of consistency between LCI and LCCA in the process of evaluation, which is also because both of them take pavement as the evaluation object. There are overlaps between the two methods. Many calculations are done by budget method. Both of them are the selection methods of multi-plan comparison, highlighting the differences of multi-plan while downplaying or ignoring the evaluation of the similarities of multi-plan. The biggest difference between the two lies in the different evaluation objectives: LCCA aims at the economic cost, while LCI aims at the environmental impact.

construction. This process includes not only the environmental impact of the production process of materials such as asphalt, cement, and aggregates but also the transportation and mixing processes of these materials [35]. The environmental impact calculation method at this stage is similar to the budget estimate. The overall environmental impact is calculated via the product of the amount of material and equipment used and the environmental impact per unit amount. The environmental impact per unit can be determined by the product of energy consumption per unit and the environmental impact of energy

Integrated Life Cycle Economic and Environmental Impact Assessment for Transportation…

Taking carbon emissions as an example, if there are n species of energy and m(i)

Energy consumption iðÞ� Carbon emissionsper unit

Materials or equipments consumption j ð Þ

� Energy consumption per unit

The production process of some materials is relatively complicated, and the environmental impact per unit is difficult to obtain quickly. For example, asphalt as a petrochemical product is one of the many products in the petrochemical industry. Environmental impacts need to be further counted and distributed to each product, and its production process varies with region and time, making it difficult to obtain an accurate value [36]. Therefore, the collection of these data is difficult to achieve through individual behavior, and it requires the efforts of governments

Countries such as Europe and the United States have been working on this aspect earlier and have obtained a lot of relatively reliable data. In developed countries, work in this area is mostly carried out and supervised by industry associations such as asphalt associations and concrete associations, and they, respectively, investigate and collect environmental impacts of products in their industry [37]. It is worth noting that the data collection and environmental impact assessment methods coordinated by industry associations are not necessarily input–out-

(2)

(3)

types of material or equipment that consume the ith energy, the total carbon emissions can be calculated using Eq. (2) along with Eq. (3). Other kinds of impacts

> n i¼1

> > m ið Þ j¼1

combustion per unit.

General pavement life cycle.

DOI: http://dx.doi.org/10.5772/intechopen.86854

Figure 4.

and organizations.

99

can be calculated in a similar way:

Energy consumption iðÞ¼ ∑

put LCA methods. In fact, they use PLCA more.

Total carbon emissions ¼ ∑

#### Figure 3. Differences and similarities between LCA and LCCA.

Since LCCA and LCI have a lot of similarities between the process and the framework, it is possible to take both LCCA and LCI into account. Compared with LCCA's classification method based on undertaking subject, LCI's spatiotemporal sequence is relatively easier to understand and operate, and LCA's framework is also more extensive and logical. Therefore, it is possible to integrate LCCA's evaluation goals into the process of LCI to realize synchronous analysis of economic cost and environmental impact.

#### 6.1 Goal and scope

The research goal that should be identified includes the cause of the research, the intended use of the research results, the intended users, and publicity; the scope of the study to be determined includes the research object and its functional units, system boundaries, boundary conditions, impact assessment methods and categories, interpretation methods, assumptions, limitations, and other various research elements. The research objectives vary according to the collective situation of the evaluation, while the research scope such as functional units and system boundaries have their commonalities.

#### 6.2 Inventory analysis

The inventory analysis step is to make statistics and calculations of the environmental impacts in each stage of the pavement life cycle, including data collection and data calculation.

Due to the complexity and protracted nature of the pavement system, this process is generally divided into several stages. The common practice divides the whole life of the pavement into five stages: raw material acquisition stage, construction stage, using stage, maintenance stage, and end of life, as shown in Figure 4.

#### 6.2.1 Raw material acquisition stage

The inventory analysis of the raw material acquisition stage mainly calculates the environmental impact of all pavement material production processes before

Integrated Life Cycle Economic and Environmental Impact Assessment for Transportation… DOI: http://dx.doi.org/10.5772/intechopen.86854

Figure 4. General pavement life cycle.

Since LCCA and LCI have a lot of similarities between the process and the framework, it is possible to take both LCCA and LCI into account. Compared with LCCA's classification method based on undertaking subject, LCI's spatiotemporal sequence is relatively easier to understand and operate, and LCA's framework is also more extensive and logical. Therefore, it is possible to integrate LCCA's evaluation goals into the process of LCI to realize synchronous analysis of economic cost and

The research goal that should be identified includes the cause of the research, the intended use of the research results, the intended users, and publicity; the scope of the study to be determined includes the research object and its functional units, system boundaries, boundary conditions, impact assessment methods and categories, interpretation methods, assumptions, limitations, and other various research elements. The research objectives vary according to the collective situation of the evaluation, while the research scope such as functional units and system boundaries

The inventory analysis step is to make statistics and calculations of the environmental impacts in each stage of the pavement life cycle, including data collection

The inventory analysis of the raw material acquisition stage mainly calculates the environmental impact of all pavement material production processes before

Due to the complexity and protracted nature of the pavement system, this process is generally divided into several stages. The common practice divides the whole life of the pavement into five stages: raw material acquisition stage, construction stage, using stage, maintenance stage, and end of life, as shown in Figure 4.

environmental impact.

Differences and similarities between LCA and LCCA.

Transportation Systems Analysis and Assessment

have their commonalities.

6.2 Inventory analysis

and data calculation.

98

6.2.1 Raw material acquisition stage

6.1 Goal and scope

Figure 3.

construction. This process includes not only the environmental impact of the production process of materials such as asphalt, cement, and aggregates but also the transportation and mixing processes of these materials [35]. The environmental impact calculation method at this stage is similar to the budget estimate. The overall environmental impact is calculated via the product of the amount of material and equipment used and the environmental impact per unit amount. The environmental impact per unit can be determined by the product of energy consumption per unit and the environmental impact of energy combustion per unit.

Taking carbon emissions as an example, if there are n species of energy and m(i) types of material or equipment that consume the ith energy, the total carbon emissions can be calculated using Eq. (2) along with Eq. (3). Other kinds of impacts can be calculated in a similar way:

$$\text{Total carbon emissions} = \sum\_{i=1}^{n} \text{Energy consumption} (i) \times \text{Carbon emissionper unit} \tag{2}$$

$$\text{Energy consumption} (\text{i}) = \sum\_{j=1}^{\text{m}(\text{i})} \text{Materials or equipment consumption} (\text{j}) \tag{3}$$

� Energy consumption per unit

The production process of some materials is relatively complicated, and the environmental impact per unit is difficult to obtain quickly. For example, asphalt as a petrochemical product is one of the many products in the petrochemical industry. Environmental impacts need to be further counted and distributed to each product, and its production process varies with region and time, making it difficult to obtain an accurate value [36]. Therefore, the collection of these data is difficult to achieve through individual behavior, and it requires the efforts of governments and organizations.

Countries such as Europe and the United States have been working on this aspect earlier and have obtained a lot of relatively reliable data. In developed countries, work in this area is mostly carried out and supervised by industry associations such as asphalt associations and concrete associations, and they, respectively, investigate and collect environmental impacts of products in their industry [37]. It is worth noting that the data collection and environmental impact assessment methods coordinated by industry associations are not necessarily input–output LCA methods. In fact, they use PLCA more.

#### 6.2.2 Construction stage

This stage mainly calculates the environmental impacts of pavement leveling, spreading, and rolling. In addition, the transportation of raw materials from the place of origin to the mixing plant and transportation from the mixing plant to the construction site are all related to this stage and can also be classified into this stage. The environmental impact calculation method at this stage is similar to the raw material acquisition stage. The overall environmental impact is calculated via the product of the amount of material and equipment used and the environmental impact per unit amount. The specific energy consumption can be calculated according to the one-shift quota and one-shift consumption of the construction code [38] and can also be analogized according to the actual situation of similar projects.

VSP ¼ Rolling resistance þ Air resistance þ Inertial and Gradient resistance

Integrated Life Cycle Economic and Environmental Impact Assessment for Transportation…

<sup>M</sup> <sup>þ</sup> <sup>F</sup>Inertial and Gradient � <sup>v</sup>

<sup>M</sup> ð Þ <sup>v</sup> <sup>þ</sup> vw <sup>2</sup> � <sup>v</sup> <sup>þ</sup> <sup>ð</sup>að Þþ <sup>1</sup> <sup>þ</sup> <sup>ε</sup><sup>i</sup> <sup>g</sup> � gradeÞ � <sup>v</sup>

, 20°C); v is vehicle speed (m/s); vw is vehicle upwind speed (m/s);

<sup>M</sup> � þðað Þþ <sup>1</sup> <sup>þ</sup> <sup>ε</sup><sup>i</sup> <sup>g</sup> � gradeÞ � <sup>v</sup>

where VSP is vehicle-specific power that refers to vehicle power per unit mass (W/kg), FAerodynamic is air resistance (N); FInertial and Gradient is inertia or gradient resistance (N); CR is rolling resistance coefficient; ρ<sup>a</sup> is ambient air density

factor, its value equal to the equivalent translation quality of rotating components (wheel, gear shaft, etc.) in the transmission system; grade is the gradient which is

coefficient in the MOVES model; B is the high rolling resistance and rotational loss coefficient in the MOVES model; and C is the air resistance coefficient in the

The specific power of a vehicle can be used to measure the power required to operate a vehicle under different conditions, and together with the speed of the vehicle determines the state and fuel consumption of the vehicle engine. The MOVES model simulates the operating state of each vehicle in a certain time range by calculating the specific power and speed of the vehicle running every second, and then sums the time and the number of vehicles according to the state and fuel consumption of different vehicles, finally obtain the overall fuel consumption of the

The MOVES model uses a simulation method to calculate the fuel consumption of a large number of vehicles which is relatively accurate and meticulous, but there are also many problems in its local application. First of all, due to the existence of a large number of environmental impact assessment method, this section adopts a simplified calculation method for the influence of rolling resistance on fuel con-

First, according to Wang, the linear relationship between vehicle fuel consump-

Additional fuel consumption of gasoline vehicle ¼ ðIRI–Initial IRIÞ � 0:0313 � Length � Standard fuel consumption of gasoline vehicle � Traffic volume � Length of the road

Additional fuel consumption of diesel vehicle v ¼ ðIRI–Initial IRIÞ � 0:00739 � Length � Standard fuel consumption of diesel vehicle � Traffic volume � Length of the road

Then, according to the IRI decay formula and maintenance formula, the

CumulativeESAL <sup>p</sup> <sup>þ</sup> <sup>1</sup>:<sup>15</sup> � ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

IRI change ¼ �0:6839 þ 0:6197 � Initial IRI (9)

continuous pavement parameters in a certain time can be obtained:

IRI <sup>p</sup> ¼ �0:<sup>174</sup> <sup>þ</sup> <sup>9</sup>:<sup>66</sup> � <sup>10</sup>�<sup>5</sup> � ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

the vertical rise divided by slope length; g is acceleration of gravity (m<sup>2</sup>

M

); CD is air resistance coefficient; ε<sup>i</sup> is the quality

/s); A is the rolling resistance

(5)

/s); M is

(6)

(7)

InitialIRI <sup>p</sup> (8)

<sup>M</sup> <sup>þ</sup> FAerodynamic � <sup>v</sup>

C

ρaCDAfront

� <sup>v</sup><sup>2</sup> <sup>þ</sup>

vehicle quality (kg); a is vehicle acceleration (m<sup>2</sup>

<sup>¼</sup> Frolling � <sup>v</sup>

¼ CRg � v þ

¼ A M � v þ B M

(1.207 kg/m<sup>3</sup>

MOVES model.

ffiffiffiffiffiffiffi

101

1 2

DOI: http://dx.doi.org/10.5772/intechopen.86854

Afront is vehicle windward area (m<sup>2</sup>

vehicle in a certain time and space.

sumption, which is easy to operate:

tion and IRI is introduced in Eqs. (6) and (7):

#### 6.2.3 Using stage

This stage mainly calculates the environmental impact caused by the interaction of the pavement surface with vehicles and the environment. It is the most complex phase of the pavement life cycle and the most imperfect stage so far. The pavement system as part of the entire transportation system, its performance, and behavior will have an impact on the environmental burden of vehicles and the environment [39]. For these impacts, many researchers have studied the specific influence modes and relationships from various aspects, among which the research on road rolling resistance and reflectivity is especially numerous. The following mainly introduce the environmental impact model of the pavement surface from two aspects of rolling resistance and reflectivity.

#### 6.2.3.1 Rolling resistance impact model

The rolling resistance of the pavement is the main factor affecting the vehicle consuming during the interaction between people and vehicles. There are now many models for assessing the impacts of rolling resistance on vehicle fuel consumption, which can be divided into four categories depending on whether rolling resistance changes and vehicle speed changes are considered. The more factors are included, the higher the model's simulation of the real situation and the more complex the relative model. Commonly used models include the HDM-4 model issued by the World Bank [40] that considers variable rolling resistance and constant speed and MOVES model for variable rolling resistance and vehicle speed released by the US Environmental Protection Agency [41].

Wang of the University of California Pavement Research Center (UCPRC) proposed a comprehensive rolling resistance environmental impact assessment method in 2012 [39–42]. Based on Wang's research on rolling resistance [36],

$$F\_{\text{rolling}} = \text{CR}\_2 \times \text{FCLIM} \times \left(b\_{11} \times \text{N}\_w + \text{CR}\_1 \times \left(b\_{12} \times \text{M} + b\_{13} \times v^2\right)\right) \tag{4}$$

where Frolling is the rolling resistance (N); CR<sup>1</sup> is tire type parameter; CR<sup>2</sup> is pavement characteristic parameter related to international roughness index (IRI), mean texture depth (MPD), and deflection value; FCLIM is the climatic factor; Nw is the total number of tires; b11, b12, and b<sup>13</sup> are parameters about tire type and technique; M is the vehicle quality; and v refers to vehicle speed (m/s).

Then use the MOVES model to calculate the relationship between rolling resistance and fuel consumption [35]:

Integrated Life Cycle Economic and Environmental Impact Assessment for Transportation… DOI: http://dx.doi.org/10.5772/intechopen.86854

VSP ¼ Rolling resistance þ Air resistance þ Inertial and Gradient resistance

$$\begin{aligned} \mathbf{y} &= F\_{\text{rolling}} \times \frac{\boldsymbol{\upsilon}}{M} + F\_{\text{Aerddynamic}} \times \frac{\boldsymbol{\upsilon}}{M} + F\_{\text{Inertial and Gradient}} \times \frac{\boldsymbol{\upsilon}}{M} \\\\ \mathbf{y} &= C\_R \mathbf{g} \times \boldsymbol{\upsilon} + \frac{1}{2} \frac{\rho\_a G\_D A\_{f\text{front}}}{M} (\boldsymbol{\upsilon} + \boldsymbol{\upsilon}\_w)^2 \times \boldsymbol{\upsilon} + (a(\mathbf{1} + \boldsymbol{\varepsilon}\_i) + \mathbf{g} \times grade) \times \boldsymbol{\upsilon} \\\\ \mathbf{y} &= \frac{A}{M} \times \boldsymbol{\upsilon} + \frac{B}{M} \times \boldsymbol{\upsilon}^2 + \frac{C}{M} \times + (a(\mathbf{1} + \boldsymbol{\varepsilon}\_i) + \mathbf{g} \times grade) \times \boldsymbol{\upsilon} \end{aligned} \tag{5}$$

where VSP is vehicle-specific power that refers to vehicle power per unit mass (W/kg), FAerodynamic is air resistance (N); FInertial and Gradient is inertia or gradient resistance (N); CR is rolling resistance coefficient; ρ<sup>a</sup> is ambient air density (1.207 kg/m<sup>3</sup> , 20°C); v is vehicle speed (m/s); vw is vehicle upwind speed (m/s); Afront is vehicle windward area (m<sup>2</sup> ); CD is air resistance coefficient; ε<sup>i</sup> is the quality factor, its value equal to the equivalent translation quality of rotating components (wheel, gear shaft, etc.) in the transmission system; grade is the gradient which is the vertical rise divided by slope length; g is acceleration of gravity (m<sup>2</sup> /s); M is vehicle quality (kg); a is vehicle acceleration (m<sup>2</sup> /s); A is the rolling resistance coefficient in the MOVES model; B is the high rolling resistance and rotational loss coefficient in the MOVES model; and C is the air resistance coefficient in the MOVES model.

The specific power of a vehicle can be used to measure the power required to operate a vehicle under different conditions, and together with the speed of the vehicle determines the state and fuel consumption of the vehicle engine. The MOVES model simulates the operating state of each vehicle in a certain time range by calculating the specific power and speed of the vehicle running every second, and then sums the time and the number of vehicles according to the state and fuel consumption of different vehicles, finally obtain the overall fuel consumption of the vehicle in a certain time and space.

The MOVES model uses a simulation method to calculate the fuel consumption of a large number of vehicles which is relatively accurate and meticulous, but there are also many problems in its local application. First of all, due to the existence of a large number of environmental impact assessment method, this section adopts a simplified calculation method for the influence of rolling resistance on fuel consumption, which is easy to operate:

First, according to Wang, the linear relationship between vehicle fuel consumption and IRI is introduced in Eqs. (6) and (7):

Additional fuel consumption of gasoline vehicle ¼ ðIRI–Initial IRIÞ � 0:0313 � Length

� Standard fuel consumption of gasoline vehicle � Traffic volume � Length of the road (6)

Additional fuel consumption of diesel vehicle v ¼ ðIRI–Initial IRIÞ � 0:00739 � Length � Standard fuel consumption of diesel vehicle � Traffic volume � Length of the road (7)

Then, according to the IRI decay formula and maintenance formula, the continuous pavement parameters in a certain time can be obtained:

$$
\sqrt{\text{IRI}} = -0.174 + 9.66 \times 10^{-5} \times \sqrt{\text{CumulativeESAL}} + 1.15 \times \sqrt{\text{InitialIRI}} \tag{8}
$$

IRI change ¼ �0:6839 þ 0:6197 � Initial IRI (9)

6.2.2 Construction stage

Transportation Systems Analysis and Assessment

projects.

6.2.3 Using stage

rolling resistance and reflectivity.

6.2.3.1 Rolling resistance impact model

resistance and fuel consumption [35]:

100

released by the US Environmental Protection Agency [41].

in 2012 [39–42]. Based on Wang's research on rolling resistance [36],

This stage mainly calculates the environmental impacts of pavement leveling, spreading, and rolling. In addition, the transportation of raw materials from the place of origin to the mixing plant and transportation from the mixing plant to the construction site are all related to this stage and can also be classified into this stage. The environmental impact calculation method at this stage is similar to the raw material acquisition stage. The overall environmental impact is calculated via the product of the amount of material and equipment used and the environmental impact per unit amount. The specific energy consumption can be calculated according to the one-shift quota and one-shift consumption of the construction code [38] and can also be analogized according to the actual situation of similar

This stage mainly calculates the environmental impact caused by the interaction of the pavement surface with vehicles and the environment. It is the most complex phase of the pavement life cycle and the most imperfect stage so far. The pavement system as part of the entire transportation system, its performance, and behavior will have an impact on the environmental burden of vehicles and the environment [39]. For these impacts, many researchers have studied the specific influence modes and relationships from various aspects, among which the research on road rolling resistance and reflectivity is especially numerous. The following mainly introduce the environmental impact model of the pavement surface from two aspects of

The rolling resistance of the pavement is the main factor affecting the vehicle consuming during the interaction between people and vehicles. There are now many models for assessing the impacts of rolling resistance on vehicle fuel consumption, which can be divided into four categories depending on whether rolling resistance changes and vehicle speed changes are considered. The more factors are included, the higher the model's simulation of the real situation and the more complex the relative model. Commonly used models include the HDM-4 model issued by the World Bank [40] that considers variable rolling resistance and constant speed and MOVES model for variable rolling resistance and vehicle speed

Wang of the University of California Pavement Research Center (UCPRC) proposed a comprehensive rolling resistance environmental impact assessment method

Frolling <sup>¼</sup> CR<sup>2</sup> � FCLIM � <sup>b</sup><sup>11</sup> � Nw <sup>þ</sup> CR<sup>1</sup> � <sup>b</sup><sup>12</sup> � <sup>M</sup> <sup>þ</sup> <sup>b</sup><sup>13</sup> � <sup>v</sup><sup>2</sup> (4)

where Frolling is the rolling resistance (N); CR<sup>1</sup> is tire type parameter; CR<sup>2</sup> is pavement characteristic parameter related to international roughness index (IRI), mean texture depth (MPD), and deflection value; FCLIM is the climatic factor; Nw is the total number of tires; b11, b12, and b<sup>13</sup> are parameters about tire type and technique; M is the vehicle quality; and v refers to vehicle speed (m/s).

Then use the MOVES model to calculate the relationship between rolling

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 maintenance.

amount of CO2. With the long-term use of cement pavement, the limestone in the pavement will reabsorb the CO2 in the air. This process gradually reduces the concentration of CO2 in the air and forms a negative carbon emission value. However, since the speed of absorbing CO2 is difficult to determine, this process may take several years or maybe decades or centuries [46]. In the long-term use of asphalt pavement, there will be surface runoff on the densely paved road surface, and there will be permeate water on the permeable pavement, which will bring the asphalt precipitate in the asphalt mixture into the water source. However, many studies have shown that it is unlikely that pollutants in the asphalt pavement will

Integrated Life Cycle Economic and Environmental Impact Assessment for Transportation…

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

This stage mainly calculates the environmental impact caused by different treatment methods at the end of the life of the pavement. The main disposal methods are classified into two categories: burying and recycling [48].

The disposal method of burying is to crush the pavement material and bury it. The environmental impact of this process is divided into three parts, namely, the consumption of crushing, transportation, and burying. There is little literature on the environmental burden of materials after burying, and further research is

Recycling is to break up the pavement material and use it as aggregate to be added to the new pavement material in a certain proportion. In actual engineering, there are various methods for recycling, which can be divided into thermal regeneration and cold regeneration depending on the regeneration temperature and can also be divided into on-site regeneration and in-plant regeneration according to the regeneration site. Since the recycled material comes from the old pavement system and is used in the new pavement system, how the environmental benefits brought by the circulation are distributed between the two systems is a problem still being studied and discussed. The existing distribution methods include cutoff, loss of quality, closed loop, equalization (50/50), and substitution [44]. But there is still no way to get consistent recognition. Due to the lack of data, the equalization method is the most commonly used method. Although it ignores the quantity and importance of recycled materials, it has the best maneuverability in practice [49].

There will be a large amount of labor input in the process of road construction,

maintenance, and recycling. At the same time, some direct monetary input as

reach dangerous concentrations [47].

DOI: http://dx.doi.org/10.5772/intechopen.86854

in fuel consumption of the vehicle.

6.3 Independent algorithm of LCCA

6.3.1 Labor costs and direct monetary inputs

6.2.5 End of life

needed.

103

6.2.4 Maintenance stage

### 6.2.3.2 Reflectivity impact model

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 impact.

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

$$
\Delta m\_{CO\_2} = 100 \times C \times A \times \Delta a \tag{10}
$$

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 considering time and environment.

In addition, there is another method for calculating the radiative forcing considering time variation, as shown in Eq. (11) [45]:

$$\mathbf{u} + \mathbf{0}.01\mathbf{a} = \frac{1.087 \times \mathbf{RF} \times \mathbf{t}}{0.217 \times \mathbf{t} - 44.78e^{-t/172.9} - 6.26e^{-t/18.51} - 0.22e^{-t/1.186} + \mathbf{51.26}}[\mathbf{kgCO}\_2] \tag{11}$$

The left side of this formula indicates a change in the reflectance per unit area of 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> . Because this 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 certain reliability.

#### 6.2.3.3 Impact from other factors

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

#### Integrated Life Cycle Economic and Environmental Impact Assessment for Transportation… DOI: http://dx.doi.org/10.5772/intechopen.86854

amount of CO2. With the long-term use of cement pavement, the limestone in the pavement will reabsorb the CO2 in the air. This process gradually reduces the concentration of CO2 in the air and forms a negative carbon emission value. However, since the speed of absorbing CO2 is difficult to determine, this process may take several years or maybe decades or centuries [46]. In the long-term use of asphalt pavement, there will be surface runoff on the densely paved road surface, and there will be permeate water on the permeable pavement, which will bring the asphalt precipitate in the asphalt mixture into the water source. However, many studies have shown that it is unlikely that pollutants in the asphalt pavement will reach dangerous concentrations [47].
