Factors Influencing Longitudinal Rail Movement Amplitude Derived from UAV-Based Measurements with Optimization-Based Geometric Correction

Abstract Longitudinal rail movement, or rail creep, creates maintenance and operation challenges in heavy axle load (HAL) freight corridors; it can contribute to track instability, gauge tightening, and changes in rail neutral temperature, for example. Rail creep is often described as directional net migration, but field observations show that longitudinal rail movement can also fluctuate cyclically. For this reason, longitudinal rail movement amplitude can be a useful metric to evaluate how much movement is allowed by the track’s longitudinal restraint system under given operational, geometric, and restraint-related conditions. This study presents a nonintrusive unmanned aerial vehicle (UAV)-based photogrammetric method to quantify relative longitudinal movement between rail and crossties over time. The method uses an optimization-based geometric correction leveraging track elements with dimensions approximately constant over time (i.e., tie plates, crossties, rail marks, and rail spacing), allowing geometric measurements to be extracted without ground control points. UAV surveys were conducted at discrete distances near 20 track structures, including grade crossings, turnouts, and open-deck bridges, across four US HAL corridors. The final data set included 764 crosstie observations collected three times at approximately 3-month intervals. Longitudinal rail movement amplitude was analyzed using a log-linear gamma regression model with cluster-robust inference to evaluate operational, geometric, and restraint-related variables. Results showed that structure type and distance from the structure, up to 152 m, did not have a consistent effect on movement amplitude after controlling for other factors. Directional traffic was associated with approximately 55% lower movement amplitude than bidirectional traffic; steeper grades were also associated with lower amplitudes. Crossties with two aligned, and two embedded anchors were associated with reductions in movement amplitude ( − 57 % , and − 31 % ) compared with nonanchored crossties, and a single loose anchor was associated with an increase in movement amplitude ( + 50 % ). These results can support rail restraint system design, inspection, and maintenance prioritization.