TRACK GEOMETRY MAINTENANCE MANAGEMENT SYSTEM
Willem Ebersohn, Professor in Railway Engineering, Department of Civil Engineering University of Pretoria, South Africa
Michael J. Trosino, Technical Director Clearances, Inspections & Tests, Amtrak 30th Street Station – Box 24, Philadelphia, U.S.A.
Abstract
Railroads face severe challenges as a result of demands for better service under continuously more constrained budgets. Better management systems are urgently needed to support more effective decision making. This paper will discuss the need for railroad infrastructure maintenance management systems and will describe the composition of these systems. Examples concentrating on maintaining track geometry by utilizing production maintenance work will be given. It is our intent to show how implementing a Maintenance Management System will optimize maintenance resources.
Key Words: Maintenance Management Assets, Condition, Geometry.
1. COST OF MAINTENANCE
Railroads are showing a substantial revival throughout the world. In the United States, railroads are showing a sustained growth in business, with an increased need for more transport capacity. Traditionally the easiest way to solve the capacity problem was to build new lines. It is also known that the full potential of the existing railroad capacity is not being utilized. A major bottleneck in providing this increased capacity is the competition for track time between train operations and track maintenance. This is exacerbated by ineffective and disruptive maintenance practices. Therefore the industry must first consider better utilization of available capacity by improving the management of existing infrastructure assets.
The right of way infrastructure is by far the largest investment made by the railroad. Maintenance of these assets typically accounts for between one quarter and one third of a railroads operating cost. (E.g. infrastructure expenditures on Spoornet and on Amtrak's NEC account for 23% and 31% of operating costs respectively.) Thus by better management of the maintenance activities, the railroad's maintenance managers and engineers can play an important role in improving the efficiency of the railroads operation. This in turn will improve the overall profit margin of the railroad without the need for increased capital.
Experience shows that the use of a management system which integrates the location of track assets with its successive geometrical condition measurements and production maintenance input can conservatively save up to 15% of the existing maintenance costs. This can be achieved by spending less than 2% of the maintenance cost on the development and implementation of the management system. In today's environment, with the ease of measurement and considering the size/speed of computers, it is feasible to have a proper maintenance management system in place to assist all levels of maintenance managers and engineers in their decision-making processes. In essence, such a system will equip the user with the knowledge and understanding of infrastructure's configuration and condition to target maintenance resources only to those areas needing work.
A comprehensive infrastructure management system, integrated with the other business units of a railroad will result in even more savings. It is anticipated that implementation of a comprehensive management system will result in indirect savings attributable to increased capacity with improved reliability. This will in turn allow for increased revenues due to increased business.
2. MAINTENANCE MANAGEMENT CYCLE
There are four major stages in the life of a railroad. We designate them as planning, design, construction, and operational use with maintenance. Each of these stages has important but changing impacts in terms of the influence that they have during the life of the railroad. Expenditures during the first three stages represent a relatively small portion of the total cost of establishing and operating the railroad infrastructure. Most of the cost to provide a safe and reliable railroad infrastructure is incurred while maintaining the railroad over its lifecycle.
Figure 1 shows a typical maintenance cycle consisting of the following steps and considerations. A short description of each step follows:
Step 1: Identify the need for maintenance which will consist of the following actions:
• Define the current operating requirements. • Conduct condition measurements. • Identify reoccurring problem sites. • Perform cause investigation of reoccurring problem sites. • Design alternative solutions to correct problems. • Predict performance of alternatives. • Conduct a needs analysis for maintenance work (i.e. surfacing, ditching and undercutting).
Step 2: Determine which maintenance alternative is economically justifiable.
Step 3: Plan maintenance projects to ensure the availability of the required resources.
Step 4: Schedule people, equipment, and material to complete the projects
Step 5: Assign tasks.
Step 6: Execute the planned work
Step 7: Obtain feedback to determine.
• Quality of work. • Success of work input. • Update of maintenance records.
Step 1 is primarily technical in nature and is defined as Maintenance Engineering. The remaining steps involve the control of work activities and are defined as Maintenance Management
3. TRACK GEOMETRY MAINTENANCE MANAGEMENT CYCLE
Maintaining track geometry and rail profile are common track maintenance activities. This paper will focus on maintaining track geometry. A typical tack geometry deterioration trend is shown in Figure 2. The graphs illustrate the effects of various categories of maintenance inputs with respect to track roughness.
For purposes of discussing Figure 2, track roughness is defined as an index calculated using the geometric deviation measurement and determined by the sum of squares with a summation length as expressed in the formula:
Where: n = number of measurements in the summation length. di = deviation measurement.
In the examples used in this paper the summation length is 200 ft. The deviation measurements are 62-foot mid-chord offset measurements for profile and alignment or deviation measurements for cross-level and gage. All are measured in inches.
The first section of Figure 2 shows the effect from initiation of service to an accumulation of 60 MGT of traffic. The solid line shows the change in back roughness when there is no maintenance input and the dashed line shows the change in track roughness with managed production surfacing input.
The service life of the track is substantially reduced if the track is allowed to deteriorate without any maintenance input. As traffic accumulates over the track without any effort to reduce the geometry deterioration rate, failure of the weaker components will determine the life of the track. Further, the full potential of the stronger components will not be utilized, as most of these components will now deteriorate at an accelerated rate due to the poor performance of the weaker components. As the geometric condition of the track reaches the operational limit, renewal or upgrading work will have to occur at a premature stage.
Conversely, the service life of the track can be extended by allowing the track to deteriorate to a predefined maintenance limit and then rehabilitating it through managed surfacing input to its best possible geometrical condition. In this way the full potential of the stronger components can be utilized, as the failure of the weaker components does not occur until much later in the life cycle of the track
The second cycle begins at 60 MGT following the track renewal work and extends to 120 MGT. The geometry deterioration characteristics will be the same as the first cycle if no components were improved. Should the maintenance manager find that the rates of deterioration and the corresponding levels of maintenance are unacceptable, the track can be redesigned and upgraded with premium components. The third cycle begins at 120 MGT and extends to 180 MGT. It illustrates the results of the upgrade work. The rate of track geometry deterioration is slower and the level of maintenance input required to keep the track in serviceable condition is reduced.
4. MAINTENANCE MANAGEMENT SYSTEM
Completing the steps in the maintenance management cycle described above requires a comprehensive knowledge of complex railroad component interactions. These include the relationship between the condition of the track and its structural performance; the effects on track performance of rehabilitation, renewal and upgrading; and the dynamic effects of vehicle speed and weight on the track response.
The cycle of conducting condition measurements, performing evaluations and analyses, and drawing up consistent work plans for numerous track sections several times a year involves the processing of a massive amount of data. This data consists of condition measures, traffic records, cost information, asset inventory data, and maintenance history. To simply handle and store these masses of data becomes a daunting task. Taking the next step to actually use this information to effectively manage the maintenance of the railroad's infrastructure then requires the design of a system to manage maintenance information.
In its most basic form a maintenance management system collects, correlates, and displays maintenance data. In this way, it acts as an analysis tool for the maintenance engineer. A well-designed railroad maintenance management system will accomplish the following:
• Link the management of maintenance work on the various parts of the railroad infrastructure, thus facilitating the planning and coordination of maintenance activities in all the infrastructure departments.
• Ensure that all levels of management make consistent maintenance decisions.
• Reduce maintenance costs by optimizing the use of maintenance resources.
• Provide timely feedback on the consequences of maintenance decisions.
• Expand the scope of maintenance management to other business processes of the railroad.
5. MAINTENANCE MANAGEMENT SYSTEM COMPONENTS
Maintenance Management System components are generally grouped into the following categories:
• Location and attributes of the infrastructure assets.
• Condition measurements of the assets.
• Traffic characteristics of trains operating over the line.
• Records of maintenance work input to keep the line operational.
5.1 Location and Attributes of Railroad Assets
Railroad assets are grouped into the following categories (See Table 1).
1. Line
• Layout (group of tracks on a route)
• Wayside components
2. Track Inventory
• Geometry features
• Structure components
• Roadbed features
• Appliances
Table 1 lists the infrastructure assets per category.
Table 1: Railroad Infrastructure Assets Line Track Inventory Layout Wayside Geometry Structure Roadbed Appliances Components Features Components Features Line Road crossing Horizontal Rail Sub-Ballast Detectors Code Alignment Track Bridge Vertical Alignment Joint Subgrade Impedance Seg. Bond Station Tunnel Check Rail Surface Lubricator Drain Platforms Turnout Buried Drain Derail Earthworks Rail Crossing Cross Drain Switch Heater Retaining Walls Tie Catenary Fastener Support Signal Support Anchor Signal Ballast Sign Slab Fence Bumping Block Overhead Utility Subsurface Utility Monument C & S Facilities E T Facilities Buildings
Each of the listed assets along a railroad right-of-way needs to be defined in terms of its geographic and linear location. They should also be described in terms of their attributes for management purposes.
Given the inaccuracies of the historic records, Amtrak chose to resurvey the Northeast Corridor right of way. John E. Chance & Associates, a member of the Fugro Group of Companies, were contracted to conduct an integrated high density Light Detecting and Ranging (LiDAR) and video survey. From this survey a current record of all physical assets and their location along the right of way was obtained. The integrated survey system is referred to as FLIMAP®.
6.2 Track Condition Assessments
The assessment of track conditions consists of continuous automated measurements from electro-mechanical inspection vehicles, visual evaluation of conditions by walking or hi-rail inspections, and in-service component failures.
The continuous automated measurements consist of the following:
1. Geometry Measurements
2. Ride Quality - Horizontal and Vertical Car body Accelerations
3. Rail Profile Measurements
4. Rail Flaw Detection
5. Gage Restraint Measurements
6. Vertical Track Deflection
Track inspection data and in-service component failures are individual evaluations that quantify the sub-standard conditions in track. On Amtrak these measures are being standardized and will be included in the database record along with the automated measurements.
5.3 Traffic Characteristics
Traffic characteristics consist of the number and weight of the wheels that travel over each track segment as well as the speed and composition of the trains. To predict track deterioration for maintenance planning purposes the existing traffic characteristics as well as the predicted change in traffic is required. As far as possible traffic over each segment of track must be recorded using records available from the operations department or from existing wheel load detectors.
5.4 Records of Work Input
Work input history is required for maintenance planning purposes. With this data available, the cost of work input can be quantified and the work input efficiency determined at successive condition measures.
A unified system for recording work input is being developed that will record any work input to the track for both spot and production work. This system will have the following major data recording categories for work input
1. Location information
2. Work description
3. Labor usage
4. Material usage 5. Equipment description & production details
6 MAINTENANCE MANAGEMENT TOOLS
A maintenance management system consists of a variety of tools to handle, store and analyze the maintenance management data. These tools will mainly consist of the following:
• The relational database.
• Graphic visualization tools.
• Various track performances trend analysis applications.
• What-if analysis applications.
• Budgeting tools.
6.1 The AMMTRACK©
The data in all the maintenance management system categories resides in an entity database using the geographical as well as the linear location of tie infrastructure assets as the referencing system. The referencing system is the core of the relational database that will relate the location of railroad assets and its attributes to condition, traffic characteristics, and work input (in the specific case of Amtrak's Northeast Corridor, the database AMMTRACK© refers to Amtrak's "Applied Maintenance Management System Database for Track")
The referencing of AMMTRACK© information by geographical location is a powerful feature which enables the user to view maintenance management information with other available natural, political, financial and environmental data. This non-railroad-referenced data can be superimposed onto the physical location of the: railroad. It also facilitates the use of other infrastructure information such as roads, utilities etc.
The fixed milepost and footage referencing allows practical field location of either the assets or the occurrence on the line of track of condition assessments. It is a referencing system that will accommodate changes and record events (work or condition recording) without the need of having a GPS system out in the field.
6.2 Graphic Visualization
Due to the magnitude of the data sets involved and the various sources of the data it is necessary to graphically visualize the data to verify the content.
The visualization of the data is also essential for effective maintenance management. The basis for the AMMTRACK© system is its ability to pull together the various maintenance management data sets and to interrelate them on a common track distance referencing system. Through visualization, correspondence between infrastructure assets, measured conditions, work input traffic characteristics, and resulting costs becomes readily apparent. In short visualization of the; date provides a first level analysis of railroad infrastructure performance.
Amtrak, working with Optram Inc., designed a database according to specified requirements which facilitates the visualization of the data. Optram Inc also developed software to display an electronic track chart and to view the condition and work input data. This viewer was based on previous concepts developed by the Chair in Railway Engineering at the University of Pretoria and Spoornet
6.3 Descriptive Representation of Geometry Performance
The geometric condition of a section of track is a good indicator of its serviceability or functional condition. The rate of change of the geometric condition is also an effective measure of the structural condition of the track components. (The structural condition of a track refers to structural properties such as strength and stiffness of the superstructure and substructure components.)
The descriptive representation of geometry performance is generally referred to as a geometry performance model. Performance models are designed using either empirical or deterministic analytical methods. Empirical models are based on either linear or non-linear regression analysis using historic condition measures. Deterministic models are those in which a primary response is predicted by a mechanistic model. As the speed and capacity of microcomputers increases, these models are being developed to predict track performance in a dynamic load environment The output of the deterministic models does not only predict the future geometric performance of the track, it also predicts the increase in dynamic wheel load due to the track condition deterioration.
The models are used to predict track performance and determine when and where to proactively intervene with the correct maintenance input to ensure the required track serviceability levels. These predictions are used to establish maintenance strategies and help to optimize maintenance budgets.
6.4 What-if Analysis Tools
Once the user can analyze trends and predict performance, he can determine maintenance needs. After the needs have been established the effects of budgeting constraints and changes in service levels can be analyzed using what-if evaluation tools.
6.5 Budgeting Tools
Finally the maintenance budgets and plans can be compiled based on the what-if analysis and the resources available. Tools for compiling budgets are railroad specific and will only be designed after the first four tools are operational.
7. TRACK GEOMETRY CONDITION MEASURES
7.1 Geometry car measuring principle
The most desirable way to measure track condition is to test the track under the load and operating conditions that the track sees in its normal usage. In order to accomplish this a track geometry car (TGC) that mimics the type of equipment that operates over the track should be utilized. It must also be equipped with a measuring system that can measure the track under the loads imparted by the running wheels. In the case of a freight railroad this requires a car with axle loads between 30 and 36 tons, operating at speeds between 40 and 60 MPH. At Amtrak, an Amfleet car is used with axle loads of 17 tons, operating at revenue passenger train speeds up to 125 MPH.
Amtrak's geometry car utilizes an inertia/optical system that allows measurements at high speeds. It also measures the track directly over the loads imparted by the running wheels. The use of the inertial system allows Amtrak to monitor the track according to the FRA definition (i.e. 62 foot chord measurements) which is readily understood by the field maintenance personnel. The inertial system also permits direct measurement of the space curve geometry, which is more useful in determining vehicle response to the track conditions.
7.2 FRA Measurement Requirements
7.2.1 Measurement frequency for Class 6 and up (waiver?)
A significant amount of the track in the NEC is operated at speeds in excess of 110 mph and with curving speeds that generate unbalances up to 5". The Waivers for these operations, granted to Amtrak by the FRA, included conditions governing inspection types, and frequencies.
Operation at speeds between 110 MPH and 125 MPH require testing with a track geometry car every 60 days. Operation at curving speeds generating unbalances up to 5" require testing with a track geometry car every 90 days. The testing procedure for Amtrak's TGC was developed to fulfill these requirements.
7.2.2 Geometry standards (Tabular)
Table 2 defines the geometry standards for each class of back.
Table 2: FRA Geometry Standards (Level 1) Parameter FRA Class 1 2 3 4 5 6 7 8 9
Gage 58" 57-3/4" 57-3/4" 57-1/2" 57-1/2" 57-1/4" 57-1/4" 57-1/4" 57-1/4"
Alinement (tan) 5" 3" 1-3/4" 1-1/2" 3/4" Alinement (crv) 5" 3" 1-3/4" 1-1/2" 5/8" Profile 3" 2-3/4" 2-1/4" 2" 1-1/4" Crosslevel 3" 2" 1-3/4" 1-1/4" 1" Warp (tan & crv) 3" 2-1/2" 2" 1-3/4" 1-1/2" 1-1/2" 1-1/2" 1-1/2" 1-1/2" Warp (spiral) 2" 1-3/4" 1-1/4" 1' 3/4"
Variation in Gage 1/2" 1/2" 1/2" 1/2" 31' Alinement 1/2" 1/2" 1/2" 1/2" 62' Alinement 3/4" 1/2" 1/2" 1/2" 124' Alinement 1-1/2" 1-1/4" 3/4" 1/2" 31' Profile 1-1/4" 1-1/4" 3/4" 1/2" 62' Profile 1-1/4" 1-1/4" 1-1/4" 1" 124' Profile 1-3/4" 1-1/2" 1-1/4" 1-1/4"
The Amtrak TGC operates as part of a normal revenue passenger train consist thus mimicking the operating environment exactly. High speed tracks, where VMAX is greater than 110 MPH, are measured every 30 days. Other NEC tracks are measured every 60 days. Each Assistant Division Engineer and the Track Supervisor ride over their respective territories during each test.
The TGC produces the following information in real time:
• Strip charts showing the plots of each measurement channel. Two copies are produced simultaneously, one for the geometry car record and one for the track supervisor. The supervisor typically writes notes and comments directly onto the strip chart during the test and takes the chart for his use when he leaves the car.
• Exceptions to geometry standards with two designated levels. Level 1 are exceptions to the FRA track safety limits and Level 2 are exceptions to Amtrak's defined maintenance limits. The exceptions are displayed to the Assistant Division Engineer and Supervisor, with repeat comparisons to the previous run. The geometry car operator reviews the exceptions during the run for errors and produces an exception report for the Supervisor and Assistant Division Engineer immediately following their territory.
• Curve analysis is performed for the designated curve speeds at 3 inches of unbalance. This report is printed with the exceptions.
• A Track Quality Index comprised of a running roughness for each measured parameter is calculated. The plot of this index is displayed on computer monitors and includes an overlay of the index from the previous measuring runs. The overlaid plots give an immediate indication of whether the track section remained stable or deteriorated. If the track was maintained it indicates if the work input was effective.
• Milepost location and track class information are automatically incorporated into all printed, displayed, and stored data utilizing differential GPS coordinates and dead reckoning measurements in tunnels.
Immediately following an Inspection run, the raw sensor data, processed geometry and TQI data, and exception files are transferred to the main engineering office in Philadelphia and are stored in a central database for use by engineering department personnel. The geometry, TQI, and exception files form the primary resource for display in the AMM viewer. The information flow is shown graphically in Figure 3.
A comprehensive curve database is generated for all of the measured curves at the different unbalances (up to 5"). This database is linked to the processed geometry to produce an interactive curve overlay tool used by the system surfacing units to analyze the curves and for programming work.
7.6 Exception Verification
A Level 1 and Level 2 exception verification table is created. This database is transmitted to the field offices and is also incorporated into AMM database. The field offices have to report back verification and corrective action within 3 days for Level 1 exceptions and 7 days for Level 2 exceptions. The corrective actions are entered into the database record for each exception.
8. DATA VISUALIZATION AND ANALYSIS FOR GEOMETRY MAINTENANCE MANAGEMENT
In this section the maintenance engineering cycle will be discussed. The graphic display of geometry maintenance management data for a five mile section of track is presented in Figure 4. The display consists of six vertically stacked plots representing a selected set of data. The data set demonstrates the first level of analysis using the maintenance management system referred to as visual analysis.
The first window shows the layout of the line indicating the major wayside components as well as the surface drains and insulated joints. The second window shows the earthwork configuration on the eastern side of the track.
8.1 Operating Characteristics
This section of track is part of Amtrak's high-speed Northeast Corridor mainline. The maximum authorized speed for the entire section of track, including the bridge, is 125 mph (Class 7). The measured annual traffic is 52 MGT, consisting of 37 MGT freight and 15 MGT high-speed passenger. Measured axle loads range from 19 ton to 49 ton for the freight service and from 15 ton to 33 ton for the passenger service. From this distribution, the axle loadings of the freight service typically drive the track's performance, while the operating speeds of the high speed passenger traffic determines the track class for safety and maintenance standards. Table 2 gives both the FRA safety and Amtrak maintenance requirements.
8.2 Geometry Condition
The third window in Figure 4 shows the 62 foot mid-chord left profile geometry measurement. The fourth window shows the calculated left profile running roughness as well as a comparison roughness from the previous measuring run. The fifth window shows the exception history for all geometry and ride quality measurements. The date of the inspection is used as the y-scale for window 5.
8.3 Reoccurring Problem Site Identification and Deterioration Rate
From these 5 windows the reoccurring problem sites can be identified. Two categories are evident, namely stable and unstable discontinuities. Examples of stable profile discontinuities are the insulated joints on the bridge in the first part of mile 72, the under grade bridge at milepost 75 and the turnout at milepost 77. The successive geometry measurements show little change in track performance. Unstable discontinuities are at milepost 73 plus 3100 feet, in the interlocking at milepost 75 plus 1500 feet and milepost 76 plus 3000 feet.
Figure 5 shows two examples of the deterioration rates of the two unstable sites in the section. A first-order regression was used to determine a deterioration trend for the measurements between surfacing. The first site deteriorated after surfacing at a rate that will reach the pre-surface roughness after approximately 6 months. The second site deteriorated at a rate that will reach the pre-surface roughness in approximately 18 months. In both instances the smooth adjacent sites profile roughness shows hardly any changes with traffic or surfacing.
8.4 Investigations
The discontinuities in the line, especially the unstable sites, result in shorter maintenance cycles. These sites generally drive the maintenance requirements for a section of track regardless of included good sections. The high deterioration rate at the discontinuities also results in premature failure of track components. The visualization approach highlights these sites for closer scrutiny. An investigation of the problem sites will give an indication of the cause of bad performance of the track. With this information available, corrective alternatives, designed for structural improvement, can be evaluated in terms of cost efficiency.
To conduct a proper cost analysis, the present cost of maintaining the track should be known. As an example, the last window in Figure 4 shows the surfacing maintenance input over three years.
9. CONCLUSION
Various levels of analysis can be conducted utilizing the available condition measurements and the production input information. The first level of analysis is the visual evaluation showing the frequency of maintenance input at problem sections as related to the condition measures and the location in the track. Unnecessary input in to non-problem areas is also highlighted. The next level of analysis is to relate conditions to performance. With these two levels of analysis available a cluster maintenance approach can be followed.
Using the roughness levels and change in roughness, the track can be subdivided into clusters having similar performance characteristics. The clusters are designated by deterioration rate as, fast, medium or slow. The sections deteriorating at a fast rate will need tamping every 6-to-12 months, medium every 20 months, and slow every 30 months.
If nothing is done to fix the problem areas and only a cluster maintenance approach is followed using the geometry car roughness levels and change in roughness to subdivide the track into clusters, a 10% to 15% improvement in the existing maintenance cost could be achieved.
If rough sites are fixed structurally, the deterioration rates should be the same as the adjacent smooth sections. In this instance the percentage improvement will be substantially higher but a higher level of initial investment will be required for the reconstruction upgrade. The details of the cause investigation and redesign fall outside the scope of this paper.
10. ACKNOWLEDGMENTS
The authors would like to thank the following organizations for their support in the development of the maintenance management concepts and the various facets of the project:
Amtrak Engineering; A. Conway-Smith, J. J. Cunningham and C. J. Ruppert Jr.
University of Pretoria, Department of Civil Engineering; Prof. W. Rohde and Mr. A. de Klerk.
Spoornet Mr. A.S. le Roux, Mr. P.C. Lombard and Mr. D.A. Barnard.
University of Massachusetts, Railroad Geotechnology Program; Prof. E.T. Selig.
John Chance Inc.
Optram Inc.
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