# Differences Evaluation of Pavement Roughness Distribution Based on Light Detection and Ranging Data
## 4 Lateral Distribution Evaluation of the Pavement Roughness  
### Difference Analysis of the Pavement Roughness among Multiple Survey Lines  
As stated previously, the variation in the road elevation among multiple survey lines may be influenced by various factors, such as the road slope and the vehicle axle load. Therefore, this study utilized the centerline of the field test roads as a reference line, and shifted the survey lines by a distance of \(l\) in turn to determine the elevation variation, as illustrated in Figure 7. The red line represents the road centerline, while the yellow line depicts the survey line, with a distance of \(l\) from each other. Since the straight sections were  
Figure 6: Results of the correlation test conducted between the reference value and the calculated results of the IRI.  
selected as the field test sections, a survey line can be obtained by connecting the starting and ending points with a vertical distance of \(l\) from the centerline.  
This study evaluated the variance of pavement roughness among 10 lateral survey lines extracted from a field test road. The spacing between the survey lines ranged from 0.2 m to 1.2 m, respectively, capturing the road profile comprehensively. The survey lines were obtained from different positions, including the lane lines, the wheel tracks, and the center of the lane, facilitating comparisons with the traditional approach.  
Figure 8 illustrates the IRI results obtained from different survey line spacings, revealing significant disparities in roughness measurements among different profiles within one road. The observed range of IRI values spanned from 1.12 m/km to 10.16 m/km, respectively, indicating a substantial difference of 9.04 m/km. Such variations can lead to a downgrade in the overall assessment by up to three grades. These discrepancies can be attributed to the specific location of the field test roads in the Jiading District of Shanghai, with a large presence of large and medium-sized trucks. Consequently, the pavement roughness was deemed to be relatively poor, with many road sections exhibiting IRI values exceeding 6 m/km.  
Table 1 presents the variance of IRI results obtained under different survey line spacing. The results indicate that as the spacing increases, the variance also increases, which aligns with the findings observed in Figure 8, where the IRI results from closer spacing survey lines exhibit less fluctuation. It was also uncovered that road profiles with larger distances between survey lines, particularly between different lanes, show significant differences in roughness. Of note, when the spacing was 1 m, that is, the survey lines were distributed at the wheel track (considering a standard lane width is 3.5 m, and the left and right wheelbase of the vehicle are about 1.8 m respectively), the variance of IRI results reached its maximum. Hence, it has recommended to assess the extent of road damage and consider the necessity of obtaining roughness values from multiple survey lines when conducting road roughness detection.  
Figure 7: Survey lines with different lateral distances.  
A pseudo-color map depicting the distribution of longitudinal (approximately 1500 m) and lateral (four lanes) roughness is presented in Figure 9. The IRI was calculated at a longitudinal interval of 100 m. The map highlights variations in roughness distribution across different spatial locations on the road. Notably, the inner lane exhibited higher IRI values compared to the outer lane. Moreover, areas with a poorer roughness were mainly concentrated around 3 m from the centerline, which is consistent with the observations in Figure 9. This can be attributed to the road section's characteristics, where the widened portion has undergone significant deterioration over time compared to the original road, leading to a poorer performance. In contrast, the outer side of the road, which has undergone widening, exhibited a comparatively better performance.