AS efficiency demands on railways increase, prioritising track maintenance before poor conditions cause vehicle damage or derailments is becoming more of a challenge.

As a result, the industry is turning to new technologies to optimise track maintenance planning, including use of vehicles equipped with sensors that quantify conditions and automatically report to Maintenance of Way (MoW) managers the location and severity of problems.

Ensco's Autonomous Vehicle/Track Interaction (V/TI) Monitor, which provides unattended condition-based monitoring of the interactions that take place between rail vehicles and track, is one such technology.

By equipping locomotives, passenger coaches or wagons with compact sensors, GPS and wireless communication devices, the V/TI Monitor applies a "train path free" approach that does not require use of dedicated measurement vehicles with specialised personnel onboard. This approach facilitates cost-effective and frequent condition-based monitoring of track infrastructure with 24x7 real-time automated reporting of safety critical conditions, as well as office-based automated analysis and reporting tools for longer range degradation monitoring and maintenance planning.

The basic components of the V/TI Monitor include a central CPU, mobile phone/GPS antenna, and sensors mounted in various positions on the vehicle. Each sensor is measured continuously, and when a value exceeds a predetermined threshold, a notification is created that includes the time, GPS coordinates, sensor reading, and time of the continuous sampled sensor data.

The V/TI Monitor platform is configurable and expandable for various conditions. However, the track maintenance user-base typically focuses on four primary areas of condition-based monitoring:

lateral track irregularities: typically attributed to track alignment irregularities that cause lateral vehicle excitation. Bridges are often the site of these irregularities due to settling and vehicles often experience lateral acceleration values as they pass

ensco long wavelength vertical track irregularities (pictured): typically attributed to repeated, long wavelength track top irregularities that excite the vehicle with pitch and bounce motions and result in vertical acceleration values. Common causes include poor drainage or sleeper conditions occurring in areas equal to or greater than 10m, and

short wavelength vertical track irregularities: attributed to track top irregularities situated three metres or less apart with actual displacement measurements reported in millimetres for each rail. Common detections include poor support conditions (pumping) joints or failed sleepers.

Many of these conditions are traditionally detected by a combination of track geometry recording vehicles and human inspections. And while it could potentially replace these methods, V/TI also detects conditions not evaluated by these techniques, such as wheel/rail impact or the actual measured dynamic response of revenue vehicles over a track route.

Once the detected conditions are reported via wireless communications, the back office data management is able to quantify the results using GIS and tabular-based reporting tools and apply an appropriate solution. This could include the linear and georeferencing of location detections to the track assets, automated distribution of safety or maintenance notifications to the appropriate maintainer or railway maintenance management system.

Running continuous measurements from revenue service trains can aid the struggle with data overload. The system is adaptable to local operating conditions so the appropriate thresholds are in place and only meaningful and manageable results are distributed. In addition, the system provides automated assessments of repeated condition detections and applies specialised algorithms on longer-term time intervals (such as weekly to monthly) to assist in proactive and planned maintenance initiatives.

Today there are more than 250 V/TI Monitors operating on high-speed, inter-city, metro and heavy-haul freight railways, monitoring over 64,000km of track in four countries every day.

The largest user group of V/TI monitoring technology is the North American Class I freight railways, including Canadian National, Canadian Pacific, CSX, BNSF, Norfolk Southern and Union Pacific. Each of these railways employs a fleet of V/TI Monitors for daily monitoring of urgent track maintenance needs with processes in place for field personnel notifications and response times. In several cases the reported information is integrated with the railway's maintenance planning systems for closed loop record keeping.

Data sharing

In addition, the Class Is have established an advanced "data sharing" mechanism, where if one railway's equipped rolling stock traverses another railway's track, the information is automatically distributed to both railways. This mechanism not only ensures safety or maintenance notifications go to the right place, but also increases the coverage of the instrumented fleet.

Several passenger railways are also using the system. Amtrak has deployed the V/TI Monitor on its Acela passenger trains operating on the Northeast Corridor between Washington, DC, and Boston, at speeds up to 240km/h. V/TI monitoring equipment is installed on 12 Acela coaches and six power cars and measures car-body and bogie accelerations in accordance with US Federal Railroad Administration (FRA) track safety standards, which require daily monitoring of onboard vehicle accelerations for trains operating in excess of 200km/h. The system is also used for vehicle and track maintenance planning.

The capability of the V/TI system to share information has resulted in the development of a strong user community, to the extent that a V/TI User Meeting is now held every year. Here railways gather to share experiences, discuss best practice strategies, and collaborate on technology improvements. As a result of these discussions, data mining approaches are being applied to identify clusters of low level, repeated problem locations which is helping to isolate segments of track under high stress, while reports have been presented demonstrating where proactive maintenance has been of benefit. Indeed with the system demonstrating its flexibility and strong results, the likelihood is that this user group will grow in the next few years to the benefit of all involved.