The benefits of unattended geometry measuring: frequent track geometry measurement can be a low-investment solution to track measurement for high-speed passenger railways, heavy haul freight railways, and rapid transit systems by using unattended geometry measuring systems mounted on revenue-service rail vehicles

International Railway Journal, Nov, 2004 by Roger Tracy

FOR several decades it has been the practice of railways worldwide to equip a special vehicle or passenger coach with measurement equipment that is used to gather track geometry data throughout their network. This data helps to maintain the track within safe operating standards, minimising the risk of derailments, and allows the track to be operated at commercially acceptable speeds.

These measurement vehicles have increasingly become an area of concern to railways. The cars are expensive to acquire, the cost of operating them with highly-skilled employees is very high, OEM replacement parts prices increase yearly, and there is a continual need to upgrade the technology over the life of the vehicle which is quite long.

As railways try to operate more trains on a track of finite capacity, the difficulties of timetabling a dedicated self-propelled vehicle is complex due to its non-regular schedule and the fact that it takes revenue train capacity away from the route. Even worse, due to its infrequent passage, this dedicated car identifies track infrastructure defects which require the imposition of speed restrictions and the unplanned scheduling of maintenance gangs or contractors to fix the problems within the time limits set by the rules in force for safe track operation.

The speed of a dedicated monitoring vehicle is another problem. As average running speeds increase, the ability of the dedicated vehicle to measure at or near normal track running speed is limited by the availability of high-speed vehicles. Surely the optimum method of measuring track must be with a vehicle similar to that used in normal operation which is capable of accessing the track consistently in terms of speed, axleload, and dynamic bogie behaviour. Both track and catenary geometry need to be measured within about 10% of line speed. The technology is available to do that without the use of a dedicated vehicle.

Natural obsolescence of dedicated geometry cars will take care of the problem over time, or a conscious decision can be made to adopt new proven methods to address the real time needs of safety and reducing track maintenance costs.

Electronic components and high-speed high-reliability software are changing the face of what is possible in reducing the cost of track data gathering. Wireless communication technology and the internet are now making the analysis and distribution of track measurement data a relatively simple and straightforward operation.

Engineers, computer specialists and technicians, all highly-paid professionals who were vital to the data gathering operation, are starting to assume different and more productive roles. Many railways have a goal of moving towards having less "finders" and more "fixers".

Technology advances and miniaturisation now allow the industry to move its track measurement data collection activity from a high-cost labour-driven environment to one where unattended equipment, modern communication technology and data processing can take over. Unattended geometry measurement systems (UGMS) are available and adaptable to passenger, freight, and rapid transit systems.

ImageMap UGMS track recording systems are fitted to service trains, which give track managers and engineers access to frequent track geometry data. This data will accurately reveal the rate of track deterioration at any location, provide feedback on the quality of track maintenance and renewal work, and warn of any sudden change in track quality which might be a cause for concern.

Advances over the last few years have allowed substantial changes in two key areas of track geometry measurement. First the equipment has been greatly reduced in size and overall complexity. This has the effect of increasing the mean time between failure and reducing the need for routine maintenance. In addition, the reduction in overall complexity has removed most real-time operator tasks. The second advance has been the custom engineering of electronics for track geometry measurement. This has allowed the manufacture of relatively low cost equipment in higher volumes and makes it possible for the first time to consider large-scale application of measuring systems on a significant number of locomotives or passenger coaches (see photo left).

These two advances make possible a step change in the method by which track geometry is collected. It is now possible to replace the traditional track geometry car with a pool of UGMS on a statistically determined number of service vehicles. Data from the pool will be collected automatically, checked for quality and processed at a central facility, and distributed through a secure network.

The only limitation to what vehicles can be used is in the track infrastructure manager's mind. The small lightweight sensors that are required have no adverse effect on the dynamic performance of the bogie. Space for a control box can be found in a locomotive cab, under a seat, or in a luggage rack.

Such vehicles cover thousands of kilometres of track every year in normal revenue-earning service. They have the axleloads and speeds that are important for track geometry measurement.