## 1 Introduction
### Factors Affecting Pavement Condition  
Some important factors that usually affect flexible pavement conditions are discussed briefly below. * Pavement Age  
Over time, the hardening of asphalt increases, thus making it more brittle and susceptible to cracking. In pavement performance prediction, pavement age is measured from the date of construction or from the date of the last major maintenance application. * Pavement Maintenance Types  
The type and timing of maintenance have a direct impact on the condition of the pavement. In the present study, the types of maintenance strategies to be evaluated were restricted to four only. These M&R strategies were no maintenance application, basic routine maintenance, overlay, and reconstruction. * Traffic Level  
Pavement deterioration is highly affected by traffic volume and vehicle types. The traffic level is usually expressed as the average daily traffic (ADT). To evaluate the M&R performance, road sections were categorized based on traffic level into two classes, high and low. A section of low traffic is receiving traffic of fewer than 3000 vehicles per lane per day (v/d), while a section of traffic that exceeds 3000 v/d is classified as high traffic. Predicting pavement performance is fundamental for appropriate resource allocation at the network level [7]. Reducing the prediction error of pavement deterioration aids transportation organizations to save money [8,9]. Several data-driven pavement performance models have been developed. A popular approach in pavement performance is the model  
Figure 3: Expected effects of maintenance strategies on pavement condition. of Markov prediction. To predict pavement performance, several statistical regression models are commonly utilized [10; 11; 12]. A knowledge-based expert system is one of the results of applications of artificial intelligence (AI) research to software programming. AI is a branch of computer science that studies ways of enabling computers to perform tasks that appear to require human intelligence. Expert systems are named for their essential characteristic: they provide advice for problem-solving that is derived from the knowledge of experts [13]. Expert systems typically use a set of rules and facts to make inferences that are reported as conclusions. The inference process relies heavily on theories of logical deduction. The objective of an expert system is to help the user choose among a limited set of options, within a specific context, from information that is more likely to be qualitative than quantitative. Expert systems or machine learning have become popular recently and have been successfully applied in many fields. The framework for an expert system primarily consists of the knowledge base, inference engine or inference machine, context or working memory, explanation module, and user interface. The collection of facts, rules and computational procedures for manipulating the information in the knowledge base to reach conclusions is called the control mechanism, or the inference engine. The objective of the inference engine is to find one or more conclusions for a sub-goal or a main goal of the consultation. It searches the facts and rules in the knowledge base and identifies and stores conclusions to use in new facts for subsequent inference. The context or working memory contains all the information derived from the inference process. This information describes the problem being solved, the rules that have been \"fixed,\" and the conclusions derived from them. The explanation module contains explanations for every inference made or piece of advice given. The user interface provides for dialogue between humans and machines. Knowledge acquisition and representation are the most difficult parts of building an expert system. They often require the knowledge engineer to interact intensely with one or more experts in the application domain. Not all problems are suitable for expert systems. For a successful application, there must be an expert or expert in the domain, and the problem should be specialized.