TTC OPERATED BY ENSCO, RAILWAY AGE JUNE 2025 ISSUE: Rolling stock inspection and monitoring are essential to safe and efficient railway operations for both freight and passenger trains. Today, a variety of wayside and onboard inspection technologies are used to automatically assess components such as bearings, wheels, and trucks, as well as systems that monitor the overall condition of a railcar. The East Palestine derailment highlighted the importance of automated rolling stock inspection in ensuring public safety. In the years ahead, wayside and onboard technologies will remain a central focus of the railway industry. This article explores current inspection technologies and emerging needs.
Bearing Inspection Technologies
Railcar bearings can experience various types of defects which can result in increased temperature. In some instances, a defective bearing can rise in temperature to the level of causing a bearing burn off, where the bearing and journal melt causing the railcar to be compromised and increasing the risk of derailment. Common root causes of defective bearing conditions include spalling on the raceways of the bearing, fretting between the bearing components and journal causing loose conditions of press fit components, and cracking steel roller cages caused by repeated wheel impacts from a slid flat wheel.
High temperatures in defective bearings can be detected by Hot Bearing Detectors (HBD), also known as Hot Box Detectors, which use infrared sensors to measure bearing temperature as a train passes. If a bearing exceeds a set temperature threshold, the detector issues a warning to the train crew via radio and sends data to a central operations center for further analysis and potential intervention.
Potential defects in a railcar’s roller bearings can also cause the bearings to generate abnormal sounds that can be detected by Acoustic Bearing Detectors (ABD). An ABD uses specialized microphones mounted in or near the track to detect and categorize the sounds generated by defective bearings such as spalling in a bearing’s cup, cones, or rollers.
A third method, onboard monitoring, involves mounting small sensors directly onto the bearing adapter. These devices typically measure temperature and acceleration, providing continuous real-time data as the train operates.
Wheel Inspection Technologies
Train wheels can develop several types of defects, including flat spots, out-of-round wear, spalling, shelling, and built-up tread. These irregularities can cause repeated impact forces when the wheels turn, increasing the risk of damage or failure. Wheel Impact Load Detectors (WILD) use strain gauges or similar sensors attached to the rails to measure the force of these impacts as the train passes.
Wheel profiles can also wear down in ways that increase derailment risk, such as thin flanges, thin rims, or hollow treads. Wheel Profile Detectors (WPD) use lasers and cameras to capture the shape of each wheel, providing valuable data to ensure they remain within safe limits. This data also supports predictive maintenance by showing how wheel wear evolves over time.
Truck, Brake, and Draft Sill Inspection Technologies
Various conditions can cause truck hunting, such as hollow worn wheels, worn friction wedges, and out-of-tolerance side bearings in combination with empty railcars operating on tangent track at higher speeds. This form of suspension motion results in a railcar’s truck rapidly oscillating from side to side which can cause damage to lading or potentially result in a wheel climb derailment. A Truck Hunting Detector (THD) utilizes strain gauges, or similar sensors, added to a WILD to measure lateral loads in addition to the vertical loads measured by WILD.
Normal braking of a railcar causes the brake shoes to press against the wheel tread causing the wheels to heat up. When a brake system is not functioning correctly, it may not apply enough pressure to the wheels, causing a “cold wheel.” Similarly, when the brakes are released a railcar’s brakes may become stuck and constantly apply pressure to the wheels, causing a “hot wheel.” Both hot and cold wheel temperatures can be detected using infrared sensors in Wheel Temperature Detectors (WTD) (also known as Hot/Cold Wheel Detectors). WTD are an important technology for assessing rolling stock braking health and can play an important role in routine brake inspections.
A growing area of innovation is machine vision technology, which uses high-resolution, high-speed cameras to inspect railcars visually. Systems may use area scan cameras (similar to digital cameras) or line scan cameras (similar to document scanners) to create detailed images. These images can be reviewed manually or processed with computer vision algorithms to automatically detect defects. This is especially helpful for inspecting components that are hard to access manually, such as the draft sill area beneath the railcar. For example, machine vision can identify cracked carrier plates or missing bolts that might otherwise go unnoticed.
Looking Ahead
Automated rolling stock inspection has made major strides in recent decades—and the future promises even more innovation. Technologies such as thermal imaging, fiber optic sensing, advanced acoustic analysis with artificial intelligence (AI), and sophisticated data analytics are poised to further enhance rail safety and reliability.
The Transportation Technology Center (TTC) in Pueblo, Colo., plays a vital role in advancing these technologies. With more than 50 miles of test track and specialized infrastructure, TTC offers a unique environment to test and validate inspection systems under real-world conditions. The facility supports collaboration across government, industry, and academia to accelerate innovation in rail safety.
As part of that mission, TTC hosts the Annual TTC Conference & Tour, which brings together transportation professionals to explore current research, safety technologies, and field-tested innovations. The next conference will be held October 7-8, 2025, and features technical presentations and a guided tour of the TTC facility. The tour includes a look at testing capabilities, live demonstrations, sponsored equipment displays, and an overview of key infrastructure supporting rolling stock inspection and monitoring.
To learn more about TTC’s testing capabilities, research programs, or upcoming events, visit ttc-ensco.com or ttc-conference.com.
