## 2 Materials and Methods
### Background
#### 2.2.1 Data Collection Technology  
The World Bank presents in edition No. 46 standards to measure the roughness of roads in use around the world [7]. Four classes are defined according to the reliability measure of the IRI, which are affected by equipment calibration requirements and the accuracy associated with their use. (1) Class 1 represents the highest precision standards for measuring the IRI, which equals a longitudinal profile with 0.5 mm precision in the vertical dimension as the basis for measurement. (2) Class 2 includes all other methods in which a longitudinal profile is required as the basis for IRI measurement; however, these results do not meet the accuracy conditions set for Class 1. (3) Class 3 includes measurement instruments that require the mathematical calculation to obtain the result. (4) Class 4 refers to subjective estimates of the value of the IRI, such as visual inspections [7,8]. A precise representation of the longitudinal profile is important, which is defined as an imaginary two-dimensional line that represents the surface along the path, plots the elevation of the surface, and is used to define the degree of design, to know roughness and the degree of deterioration, among other aspects [6]. This can be obtained using static or dynamic profilometers. The use of static profilometers consists of making measurements spaced in constant intervals; thus, it is necessary to define the distance between each measurement [9]. Once the longitudinal profile of the route is obtained, it is subjected to a procedure that allows the evaluation of the roughness of the road. For this purpose, some simulations record the characteristics associated with the road, based on vertical displacements induced to a standard vehicle, called the Quarter Car Model, which consists of a damped mass connected to a cushioned mass through a spring and a linear damper, in addition to representing the tire with another linear damper. In other words, the Quarter Car Model is defined as a set of inertial masses, springs, and damping systems that interact with the longitudinal profile of the road and whose resolution leads us to measure the accumulated vertical movements resulting from the irregularity that the road possesses. The dynamic equations presented in the model form a system of equations that use the longitudinal profile of the path as input data [10]. The vertical movement of the axis relative to the suspended mass is calculated and accumulated; thus, obtaining a value in units of m/km, which corresponds to the final value associated with the IRI [11]. This model simulates a vehicle's response when driving on the road at 80 km/h, and therefore allows us to consider factors such as safety, comfort, and cost of the use of vehicles [12]. For new roads, the IRI value fluctuates between 1.0 and 2.5 (m/km), and then reflect an increase of such values as the path is used [13]. Laser scanning equipment placed on the front of a van is the standard instrumentation for IRI measurement; this equipment is in the precision Class 1 category. The roughness index calculation is performed using built-in software that allows processing and analyzing the path profile independentlyof the measurement and can be used at any time after measuring roughness in the pavement [13]. The laser equipment is positioned pointing towards the ground, where the beam is reflected and returns to the sensor where it was emitted to calculate the distance traveled between the equipment and the pavement. As a result, you get a dense point cloud that accurately replicates the surface. However, it only represents a narrow road area and is an expensive procedure [1]. On the other hand, there are cheaper alternatives that consider the use of mechanically operating equipment. To do this, the Transport and Road Research Laboratory (TRRL) developed the Machine for Evaluating Roughness (MERLIN) roughness meter, based on the principle of static profilometer to obtain a low-cost, easy-to-use, and simple analysis method with reliable results [14].