Pavement roughness is an important indicator for evaluating road service performance and driving comfort. The Vehicle-Mounted Laser Road Profiler provides an efficient and accurate method for measuring pavement longitudinal profiles and calculating the International Roughness Index (IRI). This article introduces the testing method, procedures, calibration requirements, and data processing process for pavement roughness measurement using a laser road profiler, providing technical guidance for highway inspection, quality evaluation, and pavement maintenance.

1. Scope of Application

1.1 This method is applicable for measuring the International Roughness Index (IRI) of pavement using a vehicle-mounted laser road profiler to evaluate pavement roughness.

1.2 This method is applicable to pavement roughness testing under normal traffic conditions where the pavement surface is free from severe defects such as potholes and rutting, as well as standing water, ice, snow, and mud.

2. Technical Requirements for Instruments and Materials

The Vehicle-Mounted Laser Road Roughness Tester (hereinafter referred to as the “Laser Roughness Tester”) consists of a test vehicle, distance sensor, longitudinal profile elevation sensor, and main control system. The basic technical requirements are as follows:

(1) Test speed: 30–100 km/h.

(2) Sampling interval: ≤500 mm.

(3) Sensor test accuracy: 1.0 mm.

(4) Distance calibration error: ≤0.05%.

3. Test Method and Procedure

3.1 Preparation

(1) Check all sensors of the Laser Road Roughness Tester.

(2) Check the tire pressure of the test vehicle. The tire pressure shall meet the specified vehicle requirements. The tires shall be clean and free from any attached debris.

(3) Install the distance measurement device on site. Ensure that the mechanical fixing components are securely installed and that all screws are properly tightened without looseness.

(4) Inspect the Laser Road Roughness Tester. All components of the instrument shall meet the test requirements and shall be free from any damage.

(5) Turn on the system power supply, start the control software, and check the operating status of all components.

3.2 Test Procedure

(1) Before testing, the test vehicle shall be driven at the specified testing speed for 5–10 km to warm up the Laser Road Roughness Tester according to the required preheating time.

(2) Stop the test vehicle 50–100 m before the starting point of the test section. Start the pavement roughness testing system software and set the required testing parameters according to the on-site technical requirements of the test section.

(3) The driver shall operate the test vehicle within the specified testing speed range, preferably 50–80 km/h. Sudden acceleration and deceleration shall be avoided. The vehicle speed shall be reduced on sharp curves, and the vehicle shall enter the test section along the normal driving trajectory.

(4) After entering the test section, the operator shall start the data acquisition and recording program. During the test, the starting point, ending point, and other locations requiring special marks shall be accurately entered into the test data records in a timely manner.

(5) After the test vehicle leaves the test section, the operator shall stop data acquisition and recording, and restore all instrument components to their initial conditions.

(6) Check the test data files. The files shall be complete and the contents shall be valid; otherwise, the test shall be repeated.

(7) Turn off the system power supply and complete the test.

4. Data Processing

The data collected by the Laser Road Roughness Tester are relative pavement elevation values. The International Roughness Index (IRI) shall be calculated using the standard IRI calculation procedure with a 100 m evaluation interval. The IRI value shall be expressed in m/km and reported to two decimal places.

5. Correlation Test Between Laser Road Roughness Tester Measurements and International Roughness Index (IRI)

5.1 Test Conditions

(1) Select no fewer than four road sections with different pavement roughness levels. The difference between the IRI values of adjacent sections shall be greater than 1.0, and each section shall have sufficient acceleration and deceleration lengths. According to the actual distribution of IRI values on the test road, additional calibration sections may be appropriately added within specific ranges.

(2) The length of each test section shall be no less than 300 m.

(3) The pavement roughness within each test section shall be uniform, including the 50 m approach section before the test section.

(4) Select straight road sections with relatively small gradient variations. The selected sections shall have low traffic volumes to facilitate traffic management and testing operations.

(5) If multiple pavement roughness testing devices are installed on the same test vehicle, each device shall be tested separately.

(6) The test should preferably be carried out along the normal wheel paths of the traffic lane. The starting and ending points of the test sections shall be clearly marked.

5.2 Test Procedure

(1) Distance Calibration

① Select a flat, straight road section with relatively small gradient variations. The length of the section shall be no less than 500 m. Mark the starting and ending points clearly.

② Before calibration, the test vehicle shall be driven at the testing speed for 5–10 km to warm up the testing system according to the specified preheating time.

③ Align the front wheels of the test vehicle with the starting line, start the testing system, and drive the vehicle along the straight test section trajectory. Sudden acceleration or deceleration shall be avoided. When approaching the ending point, reduce the vehicle speed and stop the vehicle, ensuring that the front wheels are aligned with the ending line. Record the measured distance output. Repeat the procedure to ensure that the difference between the distance sensor measurement result and the nominal length of the test section is within the allowable error range.

(2) According to the requirements specified in Clause 3.2 of this method, conduct five repeated pavement roughness tests on the test section. The average value of the calculated IRI results shall be taken as the measured value for the road section.

(3) Determination of IRI Value:

① Use a precision leveling instrument as the reference instrument to measure the longitudinal profile elevation of the survey line on the calibration section. The sampling interval shall be 250 mm, and the elevation measurement accuracy shall be 0.5 mm. The measured longitudinal profile data shall then be processed using the standard IRI calculation procedure to obtain the IRI value of the calibration section.

② Other longitudinal profile measuring instruments that comply with the World Bank Class I pavement roughness measurement standard may also be used to determine the IRI value of the calibration section.

5.3 Test Data Processing

According to the requirements specified in Appendix C of this specification, perform regression analysis between the IRI values of each test section and the corresponding roughness tester measurement results. Establish the correlation equation, and the correlation coefficient R shall not be less than 0.99.

6. Test Report

The following technical information shall be included in the test report:

(1) Information of the Test Section (including stationing, length, and other relevant details).

(2) IRI values and their converted values.

(3) If a correlation test is conducted, the correlation equation and correlation coefficient shall also be reported.