# Pavement Performance Evaluation of Asphalt Expressway Based on Machine Learning Support Vector Machine

Authors: Qiao Sun; Guan Wang; Yanpeng Sui; Ideris Zakaria
Journal: Wireless Communications and Mobile Computing
 (2022)

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## Abstract

Pavement quality evaluation is important for pavement maintenance and is the basis for maintenance and investment decisions. With the use of asphalt pavements on highways, road maintenance problems are becoming increasingly serious. This paper introduces the prediction and evaluation of asphalt pavement and analyzes the quality evaluation methods of asphalt pavement in terms of damage degree, pavement smoothness, pavement gauge, and pavement strength. Based on this, a pavement quality evaluation based on machine learning, SVM, and other techniques is established, and a comprehensive evaluation model based on SVM, a set of asphalt pavement performance teaching materials, and a training label determination method are proposed to highlight the importance of highway asphalt pavement quality prediction and evaluation and provide reference for China’s highway construction.


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## Body

## 1. Introduction

With the expansion of domestic highway construction, the prediction and evaluation of asphalt pavement quality are particularly important. The quality of asphalt pavement is checked by actively predicting and evaluating the operational performance of asphalt pavement, controlling the risk of asphalt pavement use, establishing an effective evaluation system for asphalt pavement use quality, and improving the reliability of evaluation results. By the end of 2018, China accounted for 97% of the total highway mileage [1, 2]. Therefore, the application of artificial intelligence and mechanical learning in road engineering is inevitable. In China, the comprehensive evaluation of pavement performance is carried out according to the Road Technical Condition Evaluation Standard (JTGH20-2018) [3], which is based on each single evaluation index (excluding deflection values) with the corresponding weight, judged by calculating the product of pavement technical condition (PQI) values, and the weight of each subentry index is determined by combining expert experience to judge the importance of the index in a comprehensive manner and combined with the actual data, the primary factor of the road service function.Asphalt pavement performance is the main reference index of road operation and maintenance, so it is necessary to ensure that the evaluation results are in line with the actual situation of the road and guarantee the authenticity, validity, and objectivity of the data. When extracting asphalt pavement data, it is necessary to make reasonable use of relevant formulations and simplify the data through computer equipment to achieve work optimization and cost control. In addition, the performance of asphalt pavements can be classified and recorded according to certain attributes. For important indicators, individual evaluation methods should be used, and a combination of various important indicators should be analyzed. Based on the analysis results, a full-section asphalt pavement evaluation system can be constructed to improve the evaluation efficiency.When evaluating the performance of highway asphalt pavements, the following influencing factors should be fully considered: the type of pavement structure, such as foundation structure, foundation depth, pavement temperature and humidity, asphalt pavement grade, and the traffic flow of the evaluated section [4]. Since excessive vehicle loads and pavement humidity during highway use can lead to a certain degree of damage to the pavement structure, fractures, asphalt, and shedding and affect the pavement roughness, which seriously affects driving comfort, evaluation indexes must be adjusted, and repair and maintenance work must be carried out in a timely manner to ensure that pavement performance is not affected and to improve the accuracy of evaluation results.In the evaluation of highway asphalt pavement function, data such as pavement smoothness, antiskid coefficient, vibration characteristics, and vibration amplitude should be extracted according to the pavement operation quality, and they should be used as the basic indexes for pavement function evaluation. In the evaluation of pavement structure, the degree of pavement damage should be used as the main evaluation index, and the service life of pavement should be reasonably predicted by analyzing the bearing performance of pavement and determining the number of axial load actions that asphalt pavement can withstand [5].


## 2. Related Work

The performance of expressway is the comprehensive result of structure design, material performance, construction quality, driving load, natural factors, and maintenance. Pavement performance evaluation is the premise of mastering the technical status of pavement, evaluating the service quality of pavement, judging whether maintenance is needed, and making scientific maintenance planning. Therefore, evaluating the performance of asphalt pavement scientifically and accurately is of great significance to the efficient operation and scientific maintenance of expressway.The traditional pavement performance evaluation method is a linear or nonlinear regression model established based on actual survey data and expert evaluation [6]. These models have the characteristics of clear indicators, easy to understand, and simple calculation, but they have the disadvantages of great subjective influence and difficulty in accurately representing the actual performance of pavement [7, 8]. In recent years, different scholars have adopted different methods to study pavement performance [9]. In [10], based on information entropy and multiobjective space theory, fuzzy entropy weight multiobjective evaluation method for asphalt pavement performance evaluation is proposed. In [11], combined with T-S fuzzy theory and BP neural network, the evaluation model of expressway pavement performance was established. In [12], an analytic hierarchy process based on expert evaluation was constructed to evaluate pavement performance. To overcome the subjective defects of previous pavement performance evaluation methods, a pavement performance evaluation model based on interval linkage membership degree was established after effectively considering the complex uncertainty of evaluation indexes [13].The existing research on pavement performance evaluation mainly focuses on the model itself, but most of the models have shortcomings and defects [14]. For example, the grey theory mostly relies on the experience range of evaluation indicators. Neural network easily converges locally. Analytic hierarchy process has a large human influence factor [15]. However, there are few studies on the optimization of the evaluation indexes of specific pavement performance evaluation models, which reduces the scientificity and accuracy of the evaluation results to a certain extent [16]. Aiming at the characteristics of small volume, high dimension, and nonlinearity of asphalt pavement quality evaluation, this paper first uses the principal component method to reduce the evaluation index, forming an independent main component, then uses the analyzed main component to reduce the evaluation index, selects the main component samples to prepare the vector machine, and establishes the PCA-SVM model for expressway asphalt pavement performance evaluation. The actual performance data of Lenin circuit in 2016 are taken as an example for analysis.In order to reasonably evaluate pavement performance, [17] proposed an improved grey theory grey clustering principle in order to avoid subjectivity and uncertainty. In [18, 19], extension theory is applied to pavement performance evaluation. In [20], a Markov mixed risk model based on layered Bayesian estimation is established, and the results show that the model can perform the short-term pavement performance evaluation well. In [21], the actual dominant damage of road surface in Gansu Province is investigated to evaluate the road surface performance. The evaluation results are more consistent with the actual road surface performance in Gansu Province. In [22], a match-element extension evaluation model of road performance based on game theory is established by selecting Beijing-Harbin high-speed index, which combines Delphi method and correlation function method to establish static game.These model studies also have their own shortcomings; for example, neural network relatively easily converges locally, and analytic hierarchy process mainly determines the corresponding importance based on expert experience, so the objectivity is not strong, which reduces the accuracy of evaluation results [23]. With the rise of artificial intelligence, SVM (SVM) has been widely applied in various fields, and its effect in classification and evaluation is excellent [24, 25]. Therefore, this study adopts three optimization models to optimize the parameters of SVM and obtains the best optimization model. Finally, the model is applied to the performance evaluation of 23 sections of an expressway in Guangdong Province [26].


## 3. Methods

### 3.1. Pavement Smoothness Evaluation System

The accuracy of pavement performance evaluation is directly related to the reasonableness of the indexes selected in the evaluation system. Therefore, it is very important to determine the reasonable pavement performance evaluation indexes before studying the pavement performance evaluation methods. Based on the existing specifications and previous studies, this paper analyzes the influencing factors of pavement performance from three aspects: pavement damage, pavement structural strength, and pavement surface function. The evaluation index system is shown in Figure1.Figure 1
Evaluation index system of freeway asphalt pavement performance.From a large number of expressway asphalt pavement damage data, rut, crack, and repair are the most important damage types, accounting for a large proportion. In contrast, the pit, loose, hold package, subsidence, flooding, and other diseases account for less, because these diseases have a very huge impact on the safety of highway driving, daily once found, and will be repaired as soon as possible, so the repair of the number also indirectly reflects the damage of the road. The function of road table is an index to evaluate the service level of expressway surface, among which the driving quality and safety performance are the two most important aspects. Driving quality is related to three factors including people, vehicles, and roads. From the perspective of road surface, the main factor affecting road surface driving quality is road surface smoothness, which is commonly expressed by international smoothness index. Safety performance is usually expressed by skid resistance, and lateral force coefficient is the most commonly used skid resistance index.Through the reasonable evaluation of pavement damage, the performance of asphalt pavement can be scientifically analyzed, and the basic data can be provided for the prediction of durability and service life of asphalt pavement. At the present stage, China mainly uses the pavement damage rate calculation formulaDR to reasonably evaluate and analyze the pavement damage condition and integrates the pavement damage condition evaluation and analysis results through the PCI. The specific calculation formula is shown as follows:
(1)DR=DA×100=∑∑AijwijA×100,PCI=100−a0DRa1,where D is the sum of damaged areas of the road surface, Wi is the proportion of disasters on different roads surface, Aij is the damaged area of the road surface, and A is the area of the road surface. Under normal circumstances, a0 is 15.0, a1 is 0.412, and the unified unit square meter is adopted for this standard. The PCI evaluation standard is shown in Table 1. According to the analysis of Table 1, the more serious the pavement damage is, the worse the functional evaluation result of the pavement is, indicating that the driving safety factor and driving comfort index of the pavement are lower. The PCI is a direct mapping of the pavement damage condition. By reasonably analyzing the pavement damage rate (DR) and the PCI, the pavement durability of the expressway can be predicted scientifically. At the same time, according to the combined prediction model of expressway asphalt pavement, the decay coefficient of pavement performance is calculated reasonably, so as to formulate pavement maintenance measures scientifically and rationally and extend the service life of expressway.Table 1
PCI evaluation standard.
Evaluation standardExcellentGoodMiddlePoorBadPCI≥85≥70, <85≥55, <70≥60, <55<40


### 3.2. Evaluation and Analysis of Pavement Smoothness

In the evaluation process,IRI should be taken as the reference index to calculate RQI of road surface smoothness and complete the road surface smoothness analysis. The calculation formula of highway asphalt road quality index RQI is as follows:
(2)RQI=1001+a0ea1IRI,where a0 is the pavement roughness parameter, 0.026 is the value of expressway and first-level highway, a1 is the prediction model parameter, and 0.65 is the value of expressway and first-level highway. The evaluation criteria are shown in Table 2.Table 2
Evaluation standard of road driving quality index (RQI).
Evaluation standardExcellentGoodMiddlePoorBadRQI>90<90, ≥80<80, ≥70<70, ≥60<60IRIm⋅km−1≤2.4>2.4, ≤3.5>3.5, <4.3>4.3, ≤5.0>5.0


### 3.3. Road Rutting Condition Evaluation and Analysis

In recent years, our country highway capacity increased gradually; through the asphalt pavement of more and more heavy transport vehicles, high strength load easily leads to the production of permanent deformation of asphalt pavement and the rut formation; the highway asphalt pavement road safety coefficient is reduced, so there must be accurate evaluation of asphalt pavement rutting situation. At the present stage, rut depth (RD) is mainly used as the main reference index for rut condition evaluation and analysis in China. On this basis, pavement rut depth index RDI is reasonably calculated.


### 3.4. Pavement Structural Strength Evaluation

Before evaluating the structural strength of expressway asphalt pavement, pavement strength must be tested. At present, the strength of asphalt pavement structure is tested mainly by rebound method and core drilling method. By analyzing the relevant data of asphalt pavement strength detection of major expressways, it can be seen that when the thickness of subgrade protective layer is more than 2 cm and the diameter of asphalt mixture is greater than 0.4 cm and less than 0.6 cm, the rebound value of asphalt pavement is relatively low. In order to save the testing cost, improve the testing accuracy, and ensure the testing efficiency, the static load of asphalt subgrade can be tested by the core drilling method to determine the compressive strength of pavement and the existing quality problems. Under normal circumstances, the pavement structure static load calculation formulaS=0.004−0.01b can be used to calculate the pavement bearing performance. In the actual detection process of asphalt pavement structural strength of expressway, the detection results should be optimized by fast pressure correction method, and the pavement load should be appropriately increased with 1 h interval, and the total increase of load should not be less than two times of the rated pavement load value.Upon completion of the highway asphalt pavement structural strength detection work, there is also a need to use testing instrument; the pavement deflection value for reasonable measurement, by pavement deflection coefficient actual conducting a reasonable evaluation of plastic strain of asphalt surface size, if big deflection value measurement results, shows the asphalt pavement sections of plastic strain and the design requirements; there is a certain deviation lower wear resistance ability. The structural strength evaluation indexes of asphalt pavement of expressway are as follows:(3)PSSI=1001+a0ea1,SSI,SSL=lRl0,lR=600N−0.2A1A2A3,N=1+γ2−1x365γN1τ,where SSL is the strength coefficient of pavement structure, and its value is the ratio of pavement design bend to actual bend lR/l0, N is the accumulative equivalent axis of one lane in the design life, A1 is the highway grade coefficient, A2 is the surface type coefficient, A3 is the pavement structure type coefficient, γ is the average annual growth rate (%) of traffic volume in the design life, N1 is the bidirectional average equivalent axis in the first year of operation, τ is the structural coefficient, a0 is usually 15.71, a1 is 5.19, and this evaluation standard adopts the uniform unit millimeter. The value of PSSI evaluation standard ranges from 0 to 100. The lower the value is, the weaker the expressway pavement strength is.Generally, the state of pavement performance is expressed as “excellent, good, medium, inferior, and poor,” which is a multiclassification problem. SVM has been widely used in many classifications and applications of good, but the impact of expressway asphalt pavement performance evaluation index is more, and when reflecting information has a certain correlation between the indexes and overlaps, if SVM is directly used, the performance evaluation of highway asphalt pavement evaluation index of the defects will be harmful to the evaluation results. Principal component analysis can solve this problem effectively by linear combination of indexes. The evaluation index achieves dimensionality reduction through principal component analysis, so as to form mutually independent principal components. By using principal component training SVM, the classification decision function of expressway asphalt pavement performance can be obtained, which can effectively improve the accuracy of evaluation. Therefore, this paper combined principal component analysis and SVM to establish the PCA-SVM model as in Figure2.
(1)
Construct the initialization evaluation matrix:X=xijn×p(2)
UseZ-score method to standardize the elements in the X matrix(4)xij=xij−x¯jsj(3)
Calculate the standardized matrix(5)R=rijp×p=ZTZn−1(4)
m value is determined according to ∑i=1mλj/∑i=1pλj≥0.85, so that the utilization rate of expressway asphalt pavement performance evaluation index information can reach more than 85%. For each λj,j=1,⋯,m, solve the equations Rb=λjb, and get unit eigenvector bj0=bj/bj(5)
Transform the normalized matrixZ into the section principal component matrix(6)
Training sample set from the section principal component matrixU(7)
Choose the appropriate kernel function(8)
The cross-validation method is used to obtain the optimal penalty factorC and kernel parameters, and the quadratic optimization problem is constructed(9)
Construct the classification decision function of the highway pavement performanceFigure 2
Basic steps of the PCA-SVM model.By substituting the principal components of expressway sections that need to be evaluated into the classification decision function, the grades of the performance of each section of expressway asphalt pavement that need to be evaluated can be determined.


## 3.1. Pavement Smoothness Evaluation System

The accuracy of pavement performance evaluation is directly related to the reasonableness of the indexes selected in the evaluation system. Therefore, it is very important to determine the reasonable pavement performance evaluation indexes before studying the pavement performance evaluation methods. Based on the existing specifications and previous studies, this paper analyzes the influencing factors of pavement performance from three aspects: pavement damage, pavement structural strength, and pavement surface function. The evaluation index system is shown in Figure1.Figure 1
Evaluation index system of freeway asphalt pavement performance.From a large number of expressway asphalt pavement damage data, rut, crack, and repair are the most important damage types, accounting for a large proportion. In contrast, the pit, loose, hold package, subsidence, flooding, and other diseases account for less, because these diseases have a very huge impact on the safety of highway driving, daily once found, and will be repaired as soon as possible, so the repair of the number also indirectly reflects the damage of the road. The function of road table is an index to evaluate the service level of expressway surface, among which the driving quality and safety performance are the two most important aspects. Driving quality is related to three factors including people, vehicles, and roads. From the perspective of road surface, the main factor affecting road surface driving quality is road surface smoothness, which is commonly expressed by international smoothness index. Safety performance is usually expressed by skid resistance, and lateral force coefficient is the most commonly used skid resistance index.Through the reasonable evaluation of pavement damage, the performance of asphalt pavement can be scientifically analyzed, and the basic data can be provided for the prediction of durability and service life of asphalt pavement. At the present stage, China mainly uses the pavement damage rate calculation formulaDR to reasonably evaluate and analyze the pavement damage condition and integrates the pavement damage condition evaluation and analysis results through the PCI. The specific calculation formula is shown as follows:
(1)DR=DA×100=∑∑AijwijA×100,PCI=100−a0DRa1,where D is the sum of damaged areas of the road surface, Wi is the proportion of disasters on different roads surface, Aij is the damaged area of the road surface, and A is the area of the road surface. Under normal circumstances, a0 is 15.0, a1 is 0.412, and the unified unit square meter is adopted for this standard. The PCI evaluation standard is shown in Table 1. According to the analysis of Table 1, the more serious the pavement damage is, the worse the functional evaluation result of the pavement is, indicating that the driving safety factor and driving comfort index of the pavement are lower. The PCI is a direct mapping of the pavement damage condition. By reasonably analyzing the pavement damage rate (DR) and the PCI, the pavement durability of the expressway can be predicted scientifically. At the same time, according to the combined prediction model of expressway asphalt pavement, the decay coefficient of pavement performance is calculated reasonably, so as to formulate pavement maintenance measures scientifically and rationally and extend the service life of expressway.Table 1
PCI evaluation standard.
Evaluation standardExcellentGoodMiddlePoorBadPCI≥85≥70, <85≥55, <70≥60, <55<40


## 3.2. Evaluation and Analysis of Pavement Smoothness

In the evaluation process,IRI should be taken as the reference index to calculate RQI of road surface smoothness and complete the road surface smoothness analysis. The calculation formula of highway asphalt road quality index RQI is as follows:
(2)RQI=1001+a0ea1IRI,where a0 is the pavement roughness parameter, 0.026 is the value of expressway and first-level highway, a1 is the prediction model parameter, and 0.65 is the value of expressway and first-level highway. The evaluation criteria are shown in Table 2.Table 2
Evaluation standard of road driving quality index (RQI).
Evaluation standardExcellentGoodMiddlePoorBadRQI>90<90, ≥80<80, ≥70<70, ≥60<60IRIm⋅km−1≤2.4>2.4, ≤3.5>3.5, <4.3>4.3, ≤5.0>5.0


## 3.3. Road Rutting Condition Evaluation and Analysis

In recent years, our country highway capacity increased gradually; through the asphalt pavement of more and more heavy transport vehicles, high strength load easily leads to the production of permanent deformation of asphalt pavement and the rut formation; the highway asphalt pavement road safety coefficient is reduced, so there must be accurate evaluation of asphalt pavement rutting situation. At the present stage, rut depth (RD) is mainly used as the main reference index for rut condition evaluation and analysis in China. On this basis, pavement rut depth index RDI is reasonably calculated.


## 3.4. Pavement Structural Strength Evaluation

Before evaluating the structural strength of expressway asphalt pavement, pavement strength must be tested. At present, the strength of asphalt pavement structure is tested mainly by rebound method and core drilling method. By analyzing the relevant data of asphalt pavement strength detection of major expressways, it can be seen that when the thickness of subgrade protective layer is more than 2 cm and the diameter of asphalt mixture is greater than 0.4 cm and less than 0.6 cm, the rebound value of asphalt pavement is relatively low. In order to save the testing cost, improve the testing accuracy, and ensure the testing efficiency, the static load of asphalt subgrade can be tested by the core drilling method to determine the compressive strength of pavement and the existing quality problems. Under normal circumstances, the pavement structure static load calculation formulaS=0.004−0.01b can be used to calculate the pavement bearing performance. In the actual detection process of asphalt pavement structural strength of expressway, the detection results should be optimized by fast pressure correction method, and the pavement load should be appropriately increased with 1 h interval, and the total increase of load should not be less than two times of the rated pavement load value.Upon completion of the highway asphalt pavement structural strength detection work, there is also a need to use testing instrument; the pavement deflection value for reasonable measurement, by pavement deflection coefficient actual conducting a reasonable evaluation of plastic strain of asphalt surface size, if big deflection value measurement results, shows the asphalt pavement sections of plastic strain and the design requirements; there is a certain deviation lower wear resistance ability. The structural strength evaluation indexes of asphalt pavement of expressway are as follows:(3)PSSI=1001+a0ea1,SSI,SSL=lRl0,lR=600N−0.2A1A2A3,N=1+γ2−1x365γN1τ,where SSL is the strength coefficient of pavement structure, and its value is the ratio of pavement design bend to actual bend lR/l0, N is the accumulative equivalent axis of one lane in the design life, A1 is the highway grade coefficient, A2 is the surface type coefficient, A3 is the pavement structure type coefficient, γ is the average annual growth rate (%) of traffic volume in the design life, N1 is the bidirectional average equivalent axis in the first year of operation, τ is the structural coefficient, a0 is usually 15.71, a1 is 5.19, and this evaluation standard adopts the uniform unit millimeter. The value of PSSI evaluation standard ranges from 0 to 100. The lower the value is, the weaker the expressway pavement strength is.Generally, the state of pavement performance is expressed as “excellent, good, medium, inferior, and poor,” which is a multiclassification problem. SVM has been widely used in many classifications and applications of good, but the impact of expressway asphalt pavement performance evaluation index is more, and when reflecting information has a certain correlation between the indexes and overlaps, if SVM is directly used, the performance evaluation of highway asphalt pavement evaluation index of the defects will be harmful to the evaluation results. Principal component analysis can solve this problem effectively by linear combination of indexes. The evaluation index achieves dimensionality reduction through principal component analysis, so as to form mutually independent principal components. By using principal component training SVM, the classification decision function of expressway asphalt pavement performance can be obtained, which can effectively improve the accuracy of evaluation. Therefore, this paper combined principal component analysis and SVM to establish the PCA-SVM model as in Figure2.
(1)
Construct the initialization evaluation matrix:X=xijn×p(2)
UseZ-score method to standardize the elements in the X matrix(4)xij=xij−x¯jsj(3)
Calculate the standardized matrix(5)R=rijp×p=ZTZn−1(4)
m value is determined according to ∑i=1mλj/∑i=1pλj≥0.85, so that the utilization rate of expressway asphalt pavement performance evaluation index information can reach more than 85%. For each λj,j=1,⋯,m, solve the equations Rb=λjb, and get unit eigenvector bj0=bj/bj(5)
Transform the normalized matrixZ into the section principal component matrix(6)
Training sample set from the section principal component matrixU(7)
Choose the appropriate kernel function(8)
The cross-validation method is used to obtain the optimal penalty factorC and kernel parameters, and the quadratic optimization problem is constructed(9)
Construct the classification decision function of the highway pavement performanceFigure 2
Basic steps of the PCA-SVM model.By substituting the principal components of expressway sections that need to be evaluated into the classification decision function, the grades of the performance of each section of expressway asphalt pavement that need to be evaluated can be determined.


## 4. Case Study

A road condition survey was conducted on a highway sectionK315+990-K445+750 in a province. The main test items and equipment are shown in Table 3.Table 3
Road condition survey and testing items and equipment.
Test itemsMain testing equipmentDetection purposePCIManual survey combined with road condition detection vehicleDetermining the condition, extent, and scope of road damageRoad driving quality index (RQI)Vehicle-mounted laser flatness testerEvaluate road surface smoothnessRut depth index (RDI)Laser rutting detectorAnalysis of road rutting condition and extentPavement structural strength index (PSSI)Laser automatic deflectometerEvaluate the bearing capacity of the pavementSlip resistance index (SRI)Lateral force coefficient testEvaluation of pavement skid resistance


### 4.1. Detection and Evaluation of Asphalt Pavement

#### 4.1.1. Carriageway Pavement Disease Statistics

According to the statistical method of asphalt pavement disease area in JTGH20-2007 “Highway Technical Condition Assessment Standard,” the road pavement disease of this section is counted, and the results are shown in Table4. The road surface diseases of this section are mainly manifested as subsidence, looseness, block crack, and inclusion, supplemented by transverse cracks, longitudinal cracks, cracks, and pits.Table 4
Pavement disease statistics of carriageway.
Disease typeRoad surface damagePavement disease of the up-passing laneDownlink road surface diseaseArea (m2)Proportion (%)Area (m2)Proportion (%)Area (m2)Proportion (%)Subsidence1272.5856.49968.7360.75386.5142.77Lateral cracks0.740.02—0.003.380.36Pit3.860.18—0.000.980.11Block crack650.1328.64641.2439.18512.6151.88Loose245.6411.54—0.00—0.00Possesses38.262.55—0.00—0.00Repair———0.000.370.03Longitudinal cracks12.570.560.810.0747.644.85Total2223.78100.001610.78100.00951.49100.00


#### 4.1.2. Pavement Smoothness Analysis of Carriageway

According to JTGH20-2007 Highway Technical Condition Assessment Standard, the international roughness index (IRI) of road surface was calculated with 100 meters as an assessment unit to analyze and assess road running quality as in Figure3. The IRI values of upbound and downbound lanes are mainly 0.61-1.85 mm/km, and RQI comprehensive evaluation scores are 94.2 and 94.6, respectively, both exceeding the standard values, and the comprehensive evaluation grade is excellent. The total mileage of the 2.3 m/km section is 6 km, accounting for 2.33%, of which the upstream section is 2.3 km, accounting for 1.78%, and the downstream section is 3.7 km, accounting for 2.87%. >2.3 m/km corresponds to 90 minutes.Figure 3
Distribution ofIRI values in 100 meters of lane.In order to further understand the roughness of road surface, the distribution ofIRI<1.7,1.7−1.9,1.9−2.1,2.1−2.3, and >2.3 m/km was counted with 100 meters as an evaluation unit, and the results are shown in Table 5.Table 5
Pavement smoothness index of different grade distribution of lane.
IRIm⋅km−1RoadwayLength (km)Proportion (%)<1.7Up110.885.89Down112.286.98Across the board222.986.401.7-1.9Up9.97.62Down8.86.88Across the board18.67.261.9-2.1Up3.72.78Down2.51.87Across the board6.12.342.1-2.3Up2.61.95Down1.71.41Across the board4.21.68>2.3Up2.41.77Down3.82.88Across the board6.12.34As can be seen from Table5, the total mileage of the section IRI>2.3 m/km is 6 km, accounting for 2.33%, among which the upstream section is 2.3 km, accounting for 1.78%, and the downstream section is 3.7 km, accounting for 2.87%. IRI>2.3 m/km corresponds to an RQI score of 90. In order to ensure driving comfort, treatment should be carried out on these sections.


#### 4.1.3. Evaluation of Skid Resistance of Pavement

According to JTGH20-2007 Standard for Highway Technical Condition Assessment,SRI of road skid resistance was calculated by taking 100 meters as an assessment unit. The results are shown in Table 6. The SRI values of the ascending and descending lanes mainly ranged from 48 to 55, and the comprehensive SRI scores were 92.2 and 92.4, respectively, indicating that the comprehensive evaluation grade was excellent.Table 6
Different grades ofSRI distribution of skid resistance index of lane pavement.
SRIRoadwayLength (km)Proportion (%)<40Up1.81.33Down0.00.00Across the board1.80.6740-42Up0.20.24Down0.30.17Across the board000.60.1842-44Up0.00.00Down0.20.24Across the board0.20.1144-46Up1.71.25Down1.21.02Across the board2.81.1146-48Up2.31.87Down0.80.72Across the board3.41.29>48Up122.896.36Down122.397.90Across the board249.296.64


#### 4.1.4. Pavement Structural Strength Analysis and Evaluation

The laser bending detection instrument was used to conduct sampling inspection on part of the carriageway with a sampling length of 149.635 km. The detection results are shown in Table7 and Figure 4.Table 7
Grade distribution of pavement structural strength indexPSSI evaluation.
RatingUpstream PSSI rating distributionDownstream PSSI rating distributionThe distribution of PSSI assessment grades across the boardLength (km)Proportion (%)Length (km)Proportion (%)Length (km)Proportion (%)Excellent4772.727390.0012282.20Good1422.7488.762415.08Middle23.0421.2642.06Poor11.5300.0020.69Bad00.0000.0000.00Score92.6393.2892.92GradeExcellentExcellentExcellentFigure 4
Lane represents the kilometer distribution of deflection value.It can be seen from Table7 and Figure 4 that the comprehensive score of PSSI of the upstream and downstream is 92.52 and 93.29, respectively, and the comprehensive score of PSSI of the whole line is 92.91, which indicates that the comprehensive evaluation grade is excellent. The overall performance of pavement structural strength of this section is good.The pavement performance test data of the expressway (see Table8) were used to evaluate the PCI and rut depth indexRDI.Table 8
Performance index values of expressway from 2015 to 2020.
YearPCIRDIYearPCIRDI201599.996201898.491.2201699.795.1201996.588.2201799.393.3202094.385.7


### 4.2. Evaluation ofPCI

The highwayPCI decay equation model and evaluation curve were established based on the road condition data from 2015 to 2020 (see Equation (6) and Figure 5), and the precision of PCI evaluation model was verified by using the road condition data from K23+000 to K31+000. The results are shown in Table 3.
(6)PCI=99.81−exp19.88y0.884,R2=0.998,where y is the number of years of road use since 2015.Figure 5
PCI evaluation curve of expressway.From Figure5, the PCI attenuation rate on expressways shows a trend of slowing down at first and then accelerating. After 5 to 6 years of use, PCI will drop to about 95. If no preventive maintenance measures are taken to damage the road surface and it is allowed to decay normally under natural conditions, PCI will drop to middle and below in 11 to 12 years. According to the decay equation of PCI standard, the preventive maintenance measures such as crack filling, microsurface, or slurry sealing layer implemented in the period [5.58, 11.47] can improve the pavement condition in time and reduce the subsequent maintenance funds.It can be seen from Table9 that the standard attenuation equation of PCI performance has high evaluation accuracy and relative errors are all less than 5%, which can better fit the attenuation law of PCI on expressways and analyze pavement maintenance requirements.Table 9
PCI evaluation results of expressway K23+000-K31+000 section.
Mileage station2019 PCI raw valuesConverting road age (year)PCI forecast for 20202020 PCI raw valuesRelative error (%)K23+000-K24+00096.74.8294.895.50.79K24+000-K25+00097.54.4295.493.42.16K25+000-K26+00095.85.3793.391.71.71K26+000-K27+00097.54.3695.896.30.58K27+000-K28+00097.54.4295.794.80.91K28+000-K29+00095.55.4893.193.50.38K29+000-K30+00095.15.5692.790.32.68K30+000-K31+00095.55.0394.193.21.17


### 4.3. Evaluation ofRDI

The highwayRDI decay equation model and evaluation curve were established based on the road condition data from 2015 to 2020 (see Equation (7) and Figure 6), and the accuracy of the RDI evaluation model was verified by using the road condition data from K23+000 to K31+000, and the results are shown in Table 10.
(7)RDI=96.01−exp18.97y0.697,R2=0.999.Figure 6
RDI decay curve of expressway.Table 10
RDI evaluation results of expressway K23+000-K31+000 section.
Mileage station2019 RDI raw valuesConverting road age (year)RDI forecast for 20202020 RDI raw valuesRelative error (%)K23+000-K24+00089.54.6886.786.90.28K24+000-K25+00088.25.1185.586.10.91K25+000-K26+00087.75.3484.985.71.18K26+000-K27+00090.44.1687.888.50.56K27+000-K28+00089.44.5886.987.81.27K28+000-K29+00088.64.8986.187.21.49K29+000-K30+00087.35.4584.486.21.71K30+000-K31+00089.74.4887.188.11.32The comprehensive score ofPSSI of the upstream and downstream is 92.52 and 93.29, respectively, and the comprehensive score of PSSI of the whole line is 92.91, which indicates that the comprehensive evaluation grade is excellent.From Figure6, the RDI decay rate of expressway asphalt pavement is relatively fast, and the RDI value is about 90 when it is used for 4-5 years. In this case, the pavement should be taken for medium repair. According to the standard decay equation of RDI, preventive maintenance measures such as microsurface and thin-layer cover should be implemented in the period of [4.39, 8.22]. From Table 10, the RDI standard attenuation equation of pavement performance is applied to evaluate expressway, and there is little difference between the evaluated value and the actual value, with the maximum error of 1.72%, both less than 5%.


#### 4.3.1. Cross-Validation

K-CV model cross-validation was adopted to select the optimal penalty parameterC and function parameter g, as shown in Figure 7. First, the range of C1 is 2-10~210, and the value of g1 is 2-10~210. The optimal punishment parameter is C1=0.001 and g1=0.001, and the accuracy is 97.00%. Through the primary election, as shown in Figure 8, the value range of C1 was narrowed to -2.0~2.0, and the value range of g1 was narrowed to -4.0~0.00. Meanwhile, the change interval in contour line was reduced. Finally, the optimal parameter C1 is 0.25, g1 is 0.0625, and the maximum accuracy is 99.60%.Figure 7
Contour diagram of primary selection for optimal parameters.Figure 8
Final selection contour diagram of optimal parameters.


#### 4.3.2. Particle Swarm Optimization

When the number of iterations is 200 and the population number is 20, the fitness curve of particle swarm optimization algorithm is shown in Figure9. When the optimal parameters C2 and g2 are 4.858 and 0.503, respectively, the accuracy rate reaches up to 96.67%.Figure 9
Fitness curve of particle swarm optimization.


#### 4.3.3. Genetic Algorithm

Similarly, when the number of iterations is 200 and the population number is 20, the fitness curve of the genetic algorithm is shown in Figure10. The optimal parameters C3 and g3 are 0.964 and 0.407, respectively, and the accuracy rate is 94.77%.Figure 10
Fitness curve of genetic algorithm.Three models were used to optimize the parameters of the training set. The accuracy of each model and the obtained parameters are shown in Table11.Table 11
Parameter optimization results of the three models.
ModelCgAccuracy rate (%)Cross validation model0.2520.062499.62Particle swarm optimization4.8560.503196.65Genetic algorithm0.9650.407294.78From Table11, the cross-validation model has the highest accuracy, followed by particle swarm optimization and genetic algorithm. Therefore, the author chooses the best parameters obtained by cross-validation to evaluate the pavement performance.


## 4.1. Detection and Evaluation of Asphalt Pavement

### 4.1.1. Carriageway Pavement Disease Statistics

According to the statistical method of asphalt pavement disease area in JTGH20-2007 “Highway Technical Condition Assessment Standard,” the road pavement disease of this section is counted, and the results are shown in Table4. The road surface diseases of this section are mainly manifested as subsidence, looseness, block crack, and inclusion, supplemented by transverse cracks, longitudinal cracks, cracks, and pits.Table 4
Pavement disease statistics of carriageway.
Disease typeRoad surface damagePavement disease of the up-passing laneDownlink road surface diseaseArea (m2)Proportion (%)Area (m2)Proportion (%)Area (m2)Proportion (%)Subsidence1272.5856.49968.7360.75386.5142.77Lateral cracks0.740.02—0.003.380.36Pit3.860.18—0.000.980.11Block crack650.1328.64641.2439.18512.6151.88Loose245.6411.54—0.00—0.00Possesses38.262.55—0.00—0.00Repair———0.000.370.03Longitudinal cracks12.570.560.810.0747.644.85Total2223.78100.001610.78100.00951.49100.00


### 4.1.2. Pavement Smoothness Analysis of Carriageway

According to JTGH20-2007 Highway Technical Condition Assessment Standard, the international roughness index (IRI) of road surface was calculated with 100 meters as an assessment unit to analyze and assess road running quality as in Figure3. The IRI values of upbound and downbound lanes are mainly 0.61-1.85 mm/km, and RQI comprehensive evaluation scores are 94.2 and 94.6, respectively, both exceeding the standard values, and the comprehensive evaluation grade is excellent. The total mileage of the 2.3 m/km section is 6 km, accounting for 2.33%, of which the upstream section is 2.3 km, accounting for 1.78%, and the downstream section is 3.7 km, accounting for 2.87%. >2.3 m/km corresponds to 90 minutes.Figure 3
Distribution ofIRI values in 100 meters of lane.In order to further understand the roughness of road surface, the distribution ofIRI<1.7,1.7−1.9,1.9−2.1,2.1−2.3, and >2.3 m/km was counted with 100 meters as an evaluation unit, and the results are shown in Table 5.Table 5
Pavement smoothness index of different grade distribution of lane.
IRIm⋅km−1RoadwayLength (km)Proportion (%)<1.7Up110.885.89Down112.286.98Across the board222.986.401.7-1.9Up9.97.62Down8.86.88Across the board18.67.261.9-2.1Up3.72.78Down2.51.87Across the board6.12.342.1-2.3Up2.61.95Down1.71.41Across the board4.21.68>2.3Up2.41.77Down3.82.88Across the board6.12.34As can be seen from Table5, the total mileage of the section IRI>2.3 m/km is 6 km, accounting for 2.33%, among which the upstream section is 2.3 km, accounting for 1.78%, and the downstream section is 3.7 km, accounting for 2.87%. IRI>2.3 m/km corresponds to an RQI score of 90. In order to ensure driving comfort, treatment should be carried out on these sections.


### 4.1.3. Evaluation of Skid Resistance of Pavement

According to JTGH20-2007 Standard for Highway Technical Condition Assessment,SRI of road skid resistance was calculated by taking 100 meters as an assessment unit. The results are shown in Table 6. The SRI values of the ascending and descending lanes mainly ranged from 48 to 55, and the comprehensive SRI scores were 92.2 and 92.4, respectively, indicating that the comprehensive evaluation grade was excellent.Table 6
Different grades ofSRI distribution of skid resistance index of lane pavement.
SRIRoadwayLength (km)Proportion (%)<40Up1.81.33Down0.00.00Across the board1.80.6740-42Up0.20.24Down0.30.17Across the board000.60.1842-44Up0.00.00Down0.20.24Across the board0.20.1144-46Up1.71.25Down1.21.02Across the board2.81.1146-48Up2.31.87Down0.80.72Across the board3.41.29>48Up122.896.36Down122.397.90Across the board249.296.64


### 4.1.4. Pavement Structural Strength Analysis and Evaluation

The laser bending detection instrument was used to conduct sampling inspection on part of the carriageway with a sampling length of 149.635 km. The detection results are shown in Table7 and Figure 4.Table 7
Grade distribution of pavement structural strength indexPSSI evaluation.
RatingUpstream PSSI rating distributionDownstream PSSI rating distributionThe distribution of PSSI assessment grades across the boardLength (km)Proportion (%)Length (km)Proportion (%)Length (km)Proportion (%)Excellent4772.727390.0012282.20Good1422.7488.762415.08Middle23.0421.2642.06Poor11.5300.0020.69Bad00.0000.0000.00Score92.6393.2892.92GradeExcellentExcellentExcellentFigure 4
Lane represents the kilometer distribution of deflection value.It can be seen from Table7 and Figure 4 that the comprehensive score of PSSI of the upstream and downstream is 92.52 and 93.29, respectively, and the comprehensive score of PSSI of the whole line is 92.91, which indicates that the comprehensive evaluation grade is excellent. The overall performance of pavement structural strength of this section is good.The pavement performance test data of the expressway (see Table8) were used to evaluate the PCI and rut depth indexRDI.Table 8
Performance index values of expressway from 2015 to 2020.
YearPCIRDIYearPCIRDI201599.996201898.491.2201699.795.1201996.588.2201799.393.3202094.385.7


## 4.1.1. Carriageway Pavement Disease Statistics

According to the statistical method of asphalt pavement disease area in JTGH20-2007 “Highway Technical Condition Assessment Standard,” the road pavement disease of this section is counted, and the results are shown in Table4. The road surface diseases of this section are mainly manifested as subsidence, looseness, block crack, and inclusion, supplemented by transverse cracks, longitudinal cracks, cracks, and pits.Table 4
Pavement disease statistics of carriageway.
Disease typeRoad surface damagePavement disease of the up-passing laneDownlink road surface diseaseArea (m2)Proportion (%)Area (m2)Proportion (%)Area (m2)Proportion (%)Subsidence1272.5856.49968.7360.75386.5142.77Lateral cracks0.740.02—0.003.380.36Pit3.860.18—0.000.980.11Block crack650.1328.64641.2439.18512.6151.88Loose245.6411.54—0.00—0.00Possesses38.262.55—0.00—0.00Repair———0.000.370.03Longitudinal cracks12.570.560.810.0747.644.85Total2223.78100.001610.78100.00951.49100.00


## 4.1.2. Pavement Smoothness Analysis of Carriageway

According to JTGH20-2007 Highway Technical Condition Assessment Standard, the international roughness index (IRI) of road surface was calculated with 100 meters as an assessment unit to analyze and assess road running quality as in Figure3. The IRI values of upbound and downbound lanes are mainly 0.61-1.85 mm/km, and RQI comprehensive evaluation scores are 94.2 and 94.6, respectively, both exceeding the standard values, and the comprehensive evaluation grade is excellent. The total mileage of the 2.3 m/km section is 6 km, accounting for 2.33%, of which the upstream section is 2.3 km, accounting for 1.78%, and the downstream section is 3.7 km, accounting for 2.87%. >2.3 m/km corresponds to 90 minutes.Figure 3
Distribution ofIRI values in 100 meters of lane.In order to further understand the roughness of road surface, the distribution ofIRI<1.7,1.7−1.9,1.9−2.1,2.1−2.3, and >2.3 m/km was counted with 100 meters as an evaluation unit, and the results are shown in Table 5.Table 5
Pavement smoothness index of different grade distribution of lane.
IRIm⋅km−1RoadwayLength (km)Proportion (%)<1.7Up110.885.89Down112.286.98Across the board222.986.401.7-1.9Up9.97.62Down8.86.88Across the board18.67.261.9-2.1Up3.72.78Down2.51.87Across the board6.12.342.1-2.3Up2.61.95Down1.71.41Across the board4.21.68>2.3Up2.41.77Down3.82.88Across the board6.12.34As can be seen from Table5, the total mileage of the section IRI>2.3 m/km is 6 km, accounting for 2.33%, among which the upstream section is 2.3 km, accounting for 1.78%, and the downstream section is 3.7 km, accounting for 2.87%. IRI>2.3 m/km corresponds to an RQI score of 90. In order to ensure driving comfort, treatment should be carried out on these sections.


## 4.1.3. Evaluation of Skid Resistance of Pavement

According to JTGH20-2007 Standard for Highway Technical Condition Assessment,SRI of road skid resistance was calculated by taking 100 meters as an assessment unit. The results are shown in Table 6. The SRI values of the ascending and descending lanes mainly ranged from 48 to 55, and the comprehensive SRI scores were 92.2 and 92.4, respectively, indicating that the comprehensive evaluation grade was excellent.Table 6
Different grades ofSRI distribution of skid resistance index of lane pavement.
SRIRoadwayLength (km)Proportion (%)<40Up1.81.33Down0.00.00Across the board1.80.6740-42Up0.20.24Down0.30.17Across the board000.60.1842-44Up0.00.00Down0.20.24Across the board0.20.1144-46Up1.71.25Down1.21.02Across the board2.81.1146-48Up2.31.87Down0.80.72Across the board3.41.29>48Up122.896.36Down122.397.90Across the board249.296.64


## 4.1.4. Pavement Structural Strength Analysis and Evaluation

The laser bending detection instrument was used to conduct sampling inspection on part of the carriageway with a sampling length of 149.635 km. The detection results are shown in Table7 and Figure 4.Table 7
Grade distribution of pavement structural strength indexPSSI evaluation.
RatingUpstream PSSI rating distributionDownstream PSSI rating distributionThe distribution of PSSI assessment grades across the boardLength (km)Proportion (%)Length (km)Proportion (%)Length (km)Proportion (%)Excellent4772.727390.0012282.20Good1422.7488.762415.08Middle23.0421.2642.06Poor11.5300.0020.69Bad00.0000.0000.00Score92.6393.2892.92GradeExcellentExcellentExcellentFigure 4
Lane represents the kilometer distribution of deflection value.It can be seen from Table7 and Figure 4 that the comprehensive score of PSSI of the upstream and downstream is 92.52 and 93.29, respectively, and the comprehensive score of PSSI of the whole line is 92.91, which indicates that the comprehensive evaluation grade is excellent. The overall performance of pavement structural strength of this section is good.The pavement performance test data of the expressway (see Table8) were used to evaluate the PCI and rut depth indexRDI.Table 8
Performance index values of expressway from 2015 to 2020.
YearPCIRDIYearPCIRDI201599.996201898.491.2201699.795.1201996.588.2201799.393.3202094.385.7


## 4.2. Evaluation ofPCI

The highwayPCI decay equation model and evaluation curve were established based on the road condition data from 2015 to 2020 (see Equation (6) and Figure 5), and the precision of PCI evaluation model was verified by using the road condition data from K23+000 to K31+000. The results are shown in Table 3.
(6)PCI=99.81−exp19.88y0.884,R2=0.998,where y is the number of years of road use since 2015.Figure 5
PCI evaluation curve of expressway.From Figure5, the PCI attenuation rate on expressways shows a trend of slowing down at first and then accelerating. After 5 to 6 years of use, PCI will drop to about 95. If no preventive maintenance measures are taken to damage the road surface and it is allowed to decay normally under natural conditions, PCI will drop to middle and below in 11 to 12 years. According to the decay equation of PCI standard, the preventive maintenance measures such as crack filling, microsurface, or slurry sealing layer implemented in the period [5.58, 11.47] can improve the pavement condition in time and reduce the subsequent maintenance funds.It can be seen from Table9 that the standard attenuation equation of PCI performance has high evaluation accuracy and relative errors are all less than 5%, which can better fit the attenuation law of PCI on expressways and analyze pavement maintenance requirements.Table 9
PCI evaluation results of expressway K23+000-K31+000 section.
Mileage station2019 PCI raw valuesConverting road age (year)PCI forecast for 20202020 PCI raw valuesRelative error (%)K23+000-K24+00096.74.8294.895.50.79K24+000-K25+00097.54.4295.493.42.16K25+000-K26+00095.85.3793.391.71.71K26+000-K27+00097.54.3695.896.30.58K27+000-K28+00097.54.4295.794.80.91K28+000-K29+00095.55.4893.193.50.38K29+000-K30+00095.15.5692.790.32.68K30+000-K31+00095.55.0394.193.21.17


## 4.3. Evaluation ofRDI

The highwayRDI decay equation model and evaluation curve were established based on the road condition data from 2015 to 2020 (see Equation (7) and Figure 6), and the accuracy of the RDI evaluation model was verified by using the road condition data from K23+000 to K31+000, and the results are shown in Table 10.
(7)RDI=96.01−exp18.97y0.697,R2=0.999.Figure 6
RDI decay curve of expressway.Table 10
RDI evaluation results of expressway K23+000-K31+000 section.
Mileage station2019 RDI raw valuesConverting road age (year)RDI forecast for 20202020 RDI raw valuesRelative error (%)K23+000-K24+00089.54.6886.786.90.28K24+000-K25+00088.25.1185.586.10.91K25+000-K26+00087.75.3484.985.71.18K26+000-K27+00090.44.1687.888.50.56K27+000-K28+00089.44.5886.987.81.27K28+000-K29+00088.64.8986.187.21.49K29+000-K30+00087.35.4584.486.21.71K30+000-K31+00089.74.4887.188.11.32The comprehensive score ofPSSI of the upstream and downstream is 92.52 and 93.29, respectively, and the comprehensive score of PSSI of the whole line is 92.91, which indicates that the comprehensive evaluation grade is excellent.From Figure6, the RDI decay rate of expressway asphalt pavement is relatively fast, and the RDI value is about 90 when it is used for 4-5 years. In this case, the pavement should be taken for medium repair. According to the standard decay equation of RDI, preventive maintenance measures such as microsurface and thin-layer cover should be implemented in the period of [4.39, 8.22]. From Table 10, the RDI standard attenuation equation of pavement performance is applied to evaluate expressway, and there is little difference between the evaluated value and the actual value, with the maximum error of 1.72%, both less than 5%.


### 4.3.1. Cross-Validation

K-CV model cross-validation was adopted to select the optimal penalty parameterC and function parameter g, as shown in Figure 7. First, the range of C1 is 2-10~210, and the value of g1 is 2-10~210. The optimal punishment parameter is C1=0.001 and g1=0.001, and the accuracy is 97.00%. Through the primary election, as shown in Figure 8, the value range of C1 was narrowed to -2.0~2.0, and the value range of g1 was narrowed to -4.0~0.00. Meanwhile, the change interval in contour line was reduced. Finally, the optimal parameter C1 is 0.25, g1 is 0.0625, and the maximum accuracy is 99.60%.Figure 7
Contour diagram of primary selection for optimal parameters.Figure 8
Final selection contour diagram of optimal parameters.


### 4.3.2. Particle Swarm Optimization

When the number of iterations is 200 and the population number is 20, the fitness curve of particle swarm optimization algorithm is shown in Figure9. When the optimal parameters C2 and g2 are 4.858 and 0.503, respectively, the accuracy rate reaches up to 96.67%.Figure 9
Fitness curve of particle swarm optimization.


### 4.3.3. Genetic Algorithm

Similarly, when the number of iterations is 200 and the population number is 20, the fitness curve of the genetic algorithm is shown in Figure10. The optimal parameters C3 and g3 are 0.964 and 0.407, respectively, and the accuracy rate is 94.77%.Figure 10
Fitness curve of genetic algorithm.Three models were used to optimize the parameters of the training set. The accuracy of each model and the obtained parameters are shown in Table11.Table 11
Parameter optimization results of the three models.
ModelCgAccuracy rate (%)Cross validation model0.2520.062499.62Particle swarm optimization4.8560.503196.65Genetic algorithm0.9650.407294.78From Table11, the cross-validation model has the highest accuracy, followed by particle swarm optimization and genetic algorithm. Therefore, the author chooses the best parameters obtained by cross-validation to evaluate the pavement performance.


## 4.3.1. Cross-Validation

K-CV model cross-validation was adopted to select the optimal penalty parameterC and function parameter g, as shown in Figure 7. First, the range of C1 is 2-10~210, and the value of g1 is 2-10~210. The optimal punishment parameter is C1=0.001 and g1=0.001, and the accuracy is 97.00%. Through the primary election, as shown in Figure 8, the value range of C1 was narrowed to -2.0~2.0, and the value range of g1 was narrowed to -4.0~0.00. Meanwhile, the change interval in contour line was reduced. Finally, the optimal parameter C1 is 0.25, g1 is 0.0625, and the maximum accuracy is 99.60%.Figure 7
Contour diagram of primary selection for optimal parameters.Figure 8
Final selection contour diagram of optimal parameters.


## 4.3.2. Particle Swarm Optimization

When the number of iterations is 200 and the population number is 20, the fitness curve of particle swarm optimization algorithm is shown in Figure9. When the optimal parameters C2 and g2 are 4.858 and 0.503, respectively, the accuracy rate reaches up to 96.67%.Figure 9
Fitness curve of particle swarm optimization.


## 4.3.3. Genetic Algorithm

Similarly, when the number of iterations is 200 and the population number is 20, the fitness curve of the genetic algorithm is shown in Figure10. The optimal parameters C3 and g3 are 0.964 and 0.407, respectively, and the accuracy rate is 94.77%.Figure 10
Fitness curve of genetic algorithm.Three models were used to optimize the parameters of the training set. The accuracy of each model and the obtained parameters are shown in Table11.Table 11
Parameter optimization results of the three models.
ModelCgAccuracy rate (%)Cross validation model0.2520.062499.62Particle swarm optimization4.8560.503196.65Genetic algorithm0.9650.407294.78From Table11, the cross-validation model has the highest accuracy, followed by particle swarm optimization and genetic algorithm. Therefore, the author chooses the best parameters obtained by cross-validation to evaluate the pavement performance.


## 5. Conclusion

In recent years, due to the serious damage at the initial stage of the highway, the highway maintenance time is shortened, the maintenance cost is increased, and the traffic capacity is reduced. The quality evaluation of expressway asphalt pavement is the basis of freshness keeping decision system. Accurate assessment of road conditions will enable road maintenance personnel to have a comprehensive understanding of road conditions. Aiming at the reasonable comprehensive evaluation of asphalt pavement quality, a comprehensive evaluation model based on SVM, a set of asphalt pavement performance textbooks, and a method for determining training labels are proposed. The standard attenuation equation of pavement performance is used to evaluate the expressway. The difference between the evaluation value and the actual value is small, and the maximum error is 1.72%, both less than 5%. The performance evaluation model is established according to the evaluation results. In addition, this intelligent algorithm is used to evaluate its performance and is used as particle swarm optimization algorithm and genetic algorithm to ensure the maximum accuracy of the estimation results.



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*Source: 6011916-2022-08-04.xml*