MxV RAIL R&D, RAILWAY AGE JANUARY 2026 ISSUE: As railroads continue to adopt technology to improve safety and efficiency, the effectiveness of brake systems remains a critical focus. A recent study conducted by MxV Rail under the Association of American Railroads (AAR) Strategic Research Initiative (SRI) program sheds light on the performance of cold wheel processes (CWP), which are automated methods for assessing brake system health using wheel temperature data from braking trains.
All CWPs utilize wayside detection systems to identify railcars with unusually low wheel temperatures, i.e., a potential indicator of degraded brake performance, in designated areas where air brake usage is required. These systems are used to supplement traditional departure and intermediate brake tests, especially under regulatory waivers or exemptions.
The study analyzed data from two Class I railroads and compared wheel temperature data collected before and after shop visits triggered by cold wheel (CW) alerts.
CWP Assessment
The use of CWPs has not been standardized across the industry and is highly dependent on the characteristics of the train type and the terrain where CWP is applied. Two Class I railroads provided extensive datasets: Railroad A employed the Truck Temperature Ratio (TTR) method to assess performance statistically, while Railroad B’s operations allowed the use of fixed temperature thresholds per train trip. To ensure consistency, MxV Rail normalized the data using train-based z-scores, which measured the distance of each data point from the average in a normal distribution.
It is important to consider the influence of train handling on wheel temperature readings to reduce false positives. Timing of brake applications in the vicinity of a Wheel Temperature Detector (WTD) can create false perceptions of cold wheels.
For a reasonably maintained fleet, false positives can usually be detected by assessing whether strings of neighboring cars have similar wheel temperatures. The neighboring car wheel temperature assessment is built into the TTR method used by Railroad A. For Railroad B, MxV Rail also analyzed neighboring car wheel temperatures to eliminate false positives.
Key Findings
The overall analysis revealed a statistically significant improvement in wheel temperatures following shop events, regardless of the type of repairs recorded by the shop personnel. The performance improvement suggests that CWPs are effective in identifying and addressing brake system issues, even when the repairs are not directly linked to failures in pneumatic components or brake riggings. Interestingly, as shown in Figure 1 (top), the study found that, regardless of the repairs reported, cars generally produced higher wheel temperatures after the shop visit.
Using the Kruskal-Wallis H-Test, the study confirmed that wheel temperature improvements post-repair were statistically significant (p <0.05) for both railroads. Although cars shopped for CW alerts continued to show below-average performance, the improvements suggest that CWPs contributed positively to brake system health. This observation also suggests that other processes could be added to augment CWP to further restore degraded brake performance on the alerted cars.
Conclusion
MxV Rail’s analysis supports the continued use and refinement of CWPs as a reliable method for identifying brake system issues. Noticeable wheel temperature improvements were observed post-maintenance on cars identified by CWPs. As railroads strive for safer and more efficient operations, CWPs offer a promising tool for proactive maintenance and brake-related service interruption reductions.
The Technology Digest this article is based on can be found in the MxV Rail eLibrary along with more than 1,000 other publications describing the railway research, testing and analysis available from the AAR SRI program. Explore www.mxvrail.com to learn more about MxV Rail and to register for the 31st Annual AAR Research Review, to be held April 28-30, 2026.
Reference
Wang, Yi. 2025. Effectiveness of Cold-Wheel-Based Brake Tests. Technology Digest TD25-001. AAR/MxV Rail, Pueblo, Colo.
