## 6 Conclusions  
This study investigated the limitations of Traffic Speed Deflectometer (TSD) measurements when applied to inverted asphalt pavement structures, which are characterized by a reversed stiffness hierarchy--placing a soft graded crushed stone transition layer above a stiff cement-stabilized base. This non-traditional arrangement alters the pavement's mechanical response under moving loads, particularly in terms of stress transmission and deflection propagation. As a result, conventional TSD calibration assumptions, such as the zero-deflection velocity at the reference sensor (S3500), are no longer valid, leading to substantial measurement errors.  
To address this issue, a dynamic finite-element model incorporating viscoelastic asphalt behavior and realistic moving loads was developed in ABAQUS and validated against published data. The model was used to analyze deflection slope characteristics and quantify sensor-related measurement errors across multiple structural configurations.  
The key findings are as follows:  
Deflection Characteristics: Inverted asphalt pavements exhibit multi-peak deflection slope curves, similar to those of semi-rigid base structures. However, the peak near 0.15 m from the load center is significantly higher in inverted pavements.  
Measurement Errors: The assumption of zero velocity at the reference sensor location (S3500) is invalid in inverted structures. Consequently, TSD measurements systematically underestimate deflection slope, with simulated errors reaching up to 80.1%.  
Impact on Pavement Management: Such errors can result in overestimated structural capacity, potentially leading to under-designed maintenance or deferred rehabilitation. When used in network-level pavement management systems, these inaccuracies may compromise condition assessments and resource allocation.  
Recommendations: To improve TSD applicability in inverted pavement systems, we recommend relocating the reference sensor to a position located further downstream where the deflection slope is closer to true zero [13; 31], and conducting parametric simulations to optimize sensor layouts for different pavement types.  
[PERSON] was responsible for formal analysis, and writing--original draft. [PERSON] was responsible for data sorting and visualization. [PERSON] was responsible for methodology and validation, [PERSON] was responsible for conceptualization and writing--review and editing. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Science and Technology Project of \"Competitive Selection\" in Transportation, Gansu Province (No. 2025-01) and the Youth Science Foundation of Lanzhou Jiaotong University [grant No. 2021029]. And The APC was funded by the Science and Technology Project of \"Competitive Selection\" in Transportation, Gansu Province (No. 2025-01) and the Youth Science Foundation of Lanzhou Jiaotong University [grant No. 2021029].  
Not applicable.  
The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author(s).  
Author [PERSON] was employed by the company Gansu Jiaojian Project Management Co., Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.