HIGH RAIL WEAR ON THE TEHACHAPI: PROBLEM IDENTIFICATION, ANALYSIS AND IMPLEMENTATION OF SOLUTIONS. By Dr. Jude Igwemezie, P.Eng. Applied Rail Research Technologies, 2-9446 McLaughlin Rd N, Brampton, ON L6X 4H9 Phone: 905-454-8339 Fax: 905-452-1640 Daniel Marcks Applied Rail Research Technologies, 2-9446 McLaughlin Rd N, Brampton, ON L6X 4H9 Phone: 905-454-8339 Fax: 905-452-1640 William E. Van Trump Union Pacific Railroad, 1400 Douglas Street, Omaha, NE 68179 Phone: 402-544-4147 Fax: 402-501-0324 Dwight W. Clark Union Pacific Railroad, 1400 Douglas Street, Omaha, NE 68179 Phone: 402-544-4075 Fax: 402-501-0324 Total Word Count: 3477
ABSTRACT Maintenance of the 50-mile Tehachapi line has been a challenge to the Union Pacific Railroad. UP owns and maintains this track and the BNSF has trackage rights across this track. This line has experienced high rates of curve rail wear, high lateral forces, damage to fastening systems (clips, shoulders, insulators) and ties. Several testing and analysis programs have been implemented in the past, but were unable to properly identify the root cause of the problems. This necessitated a new approach, the superelevation methodology review, recently developed by Applied Rail Research Technologies (ARRT). ARRT utilized its in-house track/train interaction software, Advanced Superelevation Toolkit (ASET/SE), to examine the superelevation requirements of each train and determine a more appropriate traffic specific superelevation for the route. ARRT discovered that there was a significant discrepancy between the superelevation required by the trains and what was available. Also, the bandwidth of superelevation required by different trains was over 10 inches, as the track superelevation was extremely under-balanced for some trains, and very much overbalanced for others. Speed and power adjustments were required in order to maintain acceptable track forces. The speed profile module (ASET/SP) was used to define areas where speed adjustments were required. Finally, the distributed power module (ASET/DP) was utilized to stipulate the power requirements and distribution of power to various trains with the goal of reducing the superelevation bandwidth to ±1.0 inch. Implementation of these solutions presented by ARRT required that the engineering and mechanical departments of UP work together towards the common goal of resolving the rail wear, fastener damage, and derailment issues along the Tehachapi.
INTRODUCTION Track maintenance today is largely a reaction to a set of inputs to which we seem to have little control over. Most of the track maintenance dollars end up in curves for issues such as rails, ties and fastener replacement, track surfacing and track re-alignment. Very little attention is paid to the track superelevation in curves. Worse still, no one knows the correct superelevation that each car in any train needs to maintain a balanced set of forces as the train negotiates a curve. When the curve superelevation is off, track forces are out of balance resulting in irregular rail wear, plate cutting of ties, fastener fatigue and fracture, rail spalling, curve movement and reduced track surfacing intervals. When the superelevation is correct, the track is more stable, track asset damage is minimized, asset life is optimized and the propensity for derailment is reduced. THE PROBLEM The Mojave Subdivision is one the toughest pieces of track to maintain. This 50-mile section of track in the UPRR Mojave Subdivision has the profile shown in Figure 1 and runs from MP330 at Caliente, CA to MP380 at Mojave, CA. UP owns and maintains this track and the BNSF has trackage rights across this track. The track has a long history of problems. These problems range from excessive rail wear (Figure 2), fastener and other component damage (Figure 3), rail seat abrasion (Figure 4) and derailments and are due to the sharp curves and steep grades that exist in this section of track. In some areas, fasteners and other track components would last only months before needing replacement, while the rail itself would need replacement within 1 year. Solutions that have been tried in correcting these problems are superelevation changes, track
speed adjustments, component improvements, with limited successes. Have tried a number of maintenance improvements and continued to experience problems, UP decided that there was a needed to evaluate the superelevation requirements from an engineering science based approach. Existing superelevations have been based on AREMA equations. Excessive rail wear and track asset damage continued because prior attempts at solving the problem failed to identify and rectify the true cause of the track issues. ANALYTICAL TOOL In April 2005, UP requested that Applied Rail Research Technologies (ARRT Inc.) look in to into the problem of the Tehachapi. UP felt that there were potential issues with the track superelevation and approached ARRT to investigate. Following discussions with UP engineers, it was decided that a review of the track superelevation along the Tehachapi would be necessary. A track/train interaction modeling software package developed by Applied Rail Research Technologies Inc (ARRT Inc) was used to examine the situation in the Tehachapi. The software, called Advanced Super-Elevation Toolkit (ASET), is typically used to assist with the resolution of problems caused by improper curve superelevation and power distribution in trains. ASET, like its name suggests, is a powerful tool designed to assist railways with optimizing the life of their most valuable assets: the rail, ties and fasteners. In performing the analyses, ASET examines train/track interaction and considers many parameters that have been ignored by current practices. ASET defines the bandwidth of superelevation required by the trains that ply a given route and computes a tonnage weighted average superelevation for every curve along the route. The result is a traffic specific superelevation profile for the given route. ASET also considers wheel climb, rail rollover and
track buckling conditions in every step of the analysis. If any of these conditions exist, the analysis will be interrupted and the location and description of this dangerous condition will be flagged. With ASET, the user can establish track superelevation based on science. ASET has three modules: ASET/SE: This module determines the bandwidth of superelevation required by all the train types that use a particular route and identifies trouble spots along the curve. ASET/SP: This module computes the optimal track speed at every location along the track for any train that uses the route in order to minimize track forces. ASET/DP: This module minimizes the bandwidth of superelevation required by different trains traveling along a set route by determining the amount of locomotive power required by the train to maintain track speed as well as the optimal distribution of the locomotive power along the train. It computes the maximum train size before DP is required based on both the coupler restriction and track force limitations and defines the impact of train size on the superelevation bandwidth along any route. Each ASET module: a) Handles bi-directional traffic through any and all terrain, b) Accommodates distributed power, c) Provides drawbar forces, d) Provides lateral forces, vertical forces and L/Vs for both rails, e) Identifies problem areas and assists in rationalizing their causes, f) Reviews train action for wheel climb, rail rollover and track buckling and, g) Identifies potential locations for derailments.
Benefits of ASET include: Rationalization of the standards, policies and procedures for railway track superelevation. The capability to develop better superelevation policies that would reduce track forces and result in: Increased rail life, Decreased rate of gauge wear on high rail, Improved tie life from reduced plate cutting and spike killing of ties, Reduced gauge widening on curves, Reduced spike failures and/or fastener damage, Extended period between track surfacing, Reduced need for lubrication, Reduced fuel costs, Reduced curve movement, Reduced negative rail cant and rail roll, Reduced incidences of derailments, and Increased ROI. In addition to drawing on field data from its database, ASET requires input of basic track parameters such as curvature, rail gauge, grade, track stiffness, rail integrity, rail type, rail lubrication, railhead profile, rail size, fastener type and resilience, and track speed. Train parameters required in the input include the car or locomotive type, wheel profiles, length, weight, height, air brake characteristics, dynamic braking requirements/restrictions, coupler type, truck type, spacing within each car or locomotive, and the marshalling of the cars and locomotives.
ASET/SE utilizes all these parameters to determine the superelevation required by every car/locomotive within each train as it travels along the track. The superelevations required by the cars are accumulated for each train. The superelevations required by all the trains that traveled the route in a given period are then accumulated and the bandwidth of superelevation is defined. From these, the tonnage dependent ASET Optimized Superelevation (AOS) for each track is obtained. In cases where an analysis was performed using ASET/DP, power requirement by each train is computed along the route and the optimal route specific distribution of the power is recommended. THE TEHACHAPI Initial analyses to determine the superelevation along the Tehachapi was performed using ASET/SE. Initial assumptions included the premise that all trains were able to make track speed. There were trains with front end power only and other trains with distributed power, including mid-train power. A total of 1,300 trains were analyzed to identify the group of trains that were most responsible for the destruction of the track asset. These 1,300 trains were representative of trains that traversed this segment of track over a one month period. Figure 5 shows the key track parameters for a 5-mile track segment between MP342 and MP347 in the Tehachapi. Figure 6 shows the bandwidth of average superelevation required by all the trains operating in either direction along that section. The worst train that traveled uphill required a minimum average superelevation of -5.5 inches whereas the worst downhill train required a maximum average superelevation of 7.5 inches. The negative superelevation from the uphill trains indicates significant string lining forces within the trains. The high positive superelevation from the downhill trains indicates significant run-in compressive forces behind the front end
locomotives. The AOS was computed and plotted with the current superelevation in Figure 7. In this case, the AOS were all above the superelevation set by the railroad. However, the large bandwidth of superelevation required by different trains renders the AOS results only partially useful. Further analysis would eventually be required to examine the how the locomotive power can be utilized to narrow the superelevation bandwidth. PRELIMINARY RESULTS AND CONCLUSIONS New 141 lb rail was installed at MP342 in October 2005. By May 2006, the rail had worn up to 3/4 inch on the gauge face as shown in Figure 8(a). Based on the results of the initial analysis, UP proceeded to adjust the superelevation at MP 342 to that recommended by ASET. By December 2005, seven months later, the rail had worn only 1 / th 16 -inch (Figure 8). This tremendous reduction in rail wear by 95% was astounding. Lubrication was improved through this area in August 2005. The results at MP342 show that there is a need to change the current theory that is the basis for determining track superelevation in high degree curvature especially in high grade territories. Additionally, various conclusions were drawn from the preliminary analysis. A high percentage of the curves in Tehachapi require more superelevation than was available at the time of the analysis. The analysis also showed that the trains causing the most damage were the westbound (downhill) Non-DPU trains. The trains causing the most string lining of track were the Eastbound (uphill) Non-DPU trains. As the Non-DPU trains were the worst offenders, there is a need to consider putting DPU on all trains that use this route to narrow the bandwidth of superelevation required by each train. Sudden changes in track speed should be avoided. Instead changes in track speed should occur over appreciable track length and the curve in the speed
transition zones should be elevated accordingly. Trains traveling in direction should have enough power to maintain track speed. Therefore, further investigation into train total power requirement and its distribution was undertaken. ASET/SP/DP ANALYSIS FOR SPEED AND DISTRIBUTED POWER REQUIREMENTS Further analysis of the train speeds showed that trains traveling Eastbound (or generally uphill) were not able to reach track speed through MP335 to MP358. In fact, the South/Eastbound trains would typically only reach speeds of 12-14 mph whereas track speed was 23 mph. Therefore, it was agreed that 23 mph was not a realistic speed for the eastbound trains. The North/Westbound trains (generally downhill) occasionally lacked the required braking capacity necessary to bring speeds down to the track speed of 23 mph over this section of track. Thus it was suggested that track speed be reduced to 20 mph within this section of the Tehachapi. Based on this speed, a new AOS was re-computed using ASET/SE. The new superelevation is shown in Figure 9. As can be seen, this new superelevation at reduced track speed is very much in line with the superelevation that had existed prior to the first analysis. Nevertheless, the bandwidth od superelevation remained substantial. Analysis of total power requirements and their distribution would follow. Analysis using ASET/DP showed that total power required by South/Eastbound trains in order to attain track speed showed that gave the following relationship: Total Power required (hp) = 0.1805 x Train Tonnage (tons) x Desired Train Speed (mph) (1)
It must be emphasized that this result is applicable only to the Tehachapi track segment that was analyzed. Drawbar limitations, based on the maximum track resistance in the Tehachapi and coupler limitations (Figure 10), suggested that train tonnage limits be reduced from 4925 tons to 4227 tons trains without distributed power. Having established the total power requirement, ASET/DP also provided the train power distribution. In order to establish the power distribution, it was necessary to specify the maximum bandwidth from set value of superelevation that would be allowed. For this analysis, the maximum bandwidth was set at ±1 inch from set superelevation. Power Distribution for Uphill Trains Different combinations of power distribution (Front power/rear power) were used on different trains for the analysis and the average deviation from set superelevation along the entire track were computed and plotted in Figure 11. From these plots, it was determined that the ratio of train power be such that the front end power is 1.0 to 2.05 times the rear end power for the uphill-south/eastbound trains. Using a power distribution ratio of 1.5, ASET/SE was used to verify the superelevation of the trains that travel uphill on the Tehachapi. The result is presented in Figure 12. As can be seen, the superelevation required by all the trains was within ±1 inch of the AOS.
Power Distribution for Downhill Trains A similar analysis was performed for trains traveling downhill. The variation of power distribution for the North/Westbound trains is shown in Figure 13. From this a power ratio of 0.6 to 1.5 (front end power divided by rear end power) was found to be adequate for downhill North/Westbound trains. Using a power distribution of 1.0, ASET/SE was used to verify the superelevation of the trains that travel downhill on the Tehachapi. The result is presented in Figure 14. As can be seen, the superelevation required by all the trains was within ±1 inch of the AOS. A ratio below 1.0 suggests the need for mid-power on the downhill trains. Using an uphill power ratio of 1.5 and a downhill power ratio of 1.0, ASET/SE analysis was performed for the 50 mile Tehachapi route. The result is shown in Figure 15. As can be seen, the bandwidth of superelevation was reduced from 12 inches in Figure 6 to 2 inches in Figure 15. CONCLUSIONS Along the Tehachapi, UP has also implemented a rigorous top of rail and gauge face lubrication program. Nonetheless, improper superelevation was identified as the most significant factor in reducing excessive flange wear on the high rail. Implementation of the conclusions drawn from the ASET analysis for superelevation and power distribution yielded an optimal situation of superelevation requirements as seen in Figure 16. The lateral forces have been minimized and track and track component life would be vastly extended. The conclusions of the ASET analysis of the Tehachapi are far-reaching and require the involvement and interaction of many of the UPRR departments. These conclusions affect train
weight, power and speed and thus, no doubt, affect train scheduling, locomotive re-assignments and possibly purchase of more power for the route, as well as track superelevation and alignment. However, there is little doubt that these changes will have dramatic effects on the life of rail and rail components as well as wheel life, as can be seen from the preliminary results already drawn from one section of the Tehachapi. Results that show a dramatic 95% reduction in rail wear will no doubt apply to other sections of the UPRR track. RECOMMENDATIONS In terms of coupler drawbar limitations, the trailing tonnage limit for non-dpu trains should be reduced from 4925 tons to 4227 tons, because the coupler limit is 235 kips. Accordingly, Maximum drawbar force (kips) = 0.0556 x Train Weight (tons). (2) Using ASET s DP recommendations will always satisfy this drawbar limitation. The track speed in the 50 mile section of the Tehachapi should be reduced from 23 mph to 20 mph, a speed that is more reasonably attainable by the Southbound (uphill) trains. It is important that both Northbound and Southbound trains travel at near the same speed. In order to attain this speed of 20 mph, Southbound trains need adequate horsepower as defined by the equation: Power Required (hp) = 0.1805 x Train Weight (tons) x (20 mph) (3) All Southbound uphill trains require distributed power in the ratio of 1.0 to 2.05 (front power /rear power) so that superelevation requirement will remain within ± 1.0 inch of the set value.
Northbound trains require enough locomotives to deliver adequate dynamic braking, such that: Max Dynamic Braking Required (lbs) = 21.088 x Train Weight (tons) (4) All Northbound trains require distributed power in the ratio of 0.6 to 1.5 (front power /rear power) so that their each Northbound downhill train s superelevation requirement will remain within ± 1.0 inch of the set value. Note that a distributed power ratio of less than 1 implies the need for mid-power.
FIGURES Figure 1: Figure 2: Figure 3: Figure 4: Figure 5: Figure 6: Figure 7: Figure 8: Track profile and timetable speed along the Tehachapi Wear on the high rail Fastener damage Rail seat abrasion Track Profile and speed for a 5-mile section of the Tehachapi The superelevation required by all trains in the Tehachapi s regular traffic mix The superelevation proposed by ASET/SE versus the previous track superelevation (a) Rail removed after 7-months in service. (b) Wear (reduced by 95%) over the same period after ASET recommendations were implemented Figure 9: The superelevation proposed by ASET/SE based on a reduction in track speed versus the previous track superelevation Figure 10: Drawbar forces versus Train Weight and Length Figure 11: A plot of the deviation between uphill- South/Eastbound train s superelevation requirement and power ratio Figure 12: Superelevation required by uphill-south/eastbound trains for a superelevation bandwidth of ±1 inch and power ratio of 1.5. Figure 13: A plot of the deviation between downhill-north/westbound train s superelevation requirement and power ratio Figure 14: Superelevation required by downhill-north/westbound trains for a superelevation bandwidth of ±1 inch and power ratio of 1.0.
Figure 15: The superelevation required by all trains in the Tehachapi under the ASET proposed train power ratio of 1.5 uphill and 1.0 downhill.
Figure 1: Track profile and timetable speed along the Tehachapi
Figure 2: Wear on the high rail
Figure 3: Fastener damage
Figure 4: Rail seat abrasion
Figure 5: Track Profile and speed for a 5-mile section of the Tehachapi
Figure 6: The superelevation required by all trains in the Tehachapi s regular traffic mix
ASET vs UPRR Superelevation Superelevation (inches) 8 7 6 5 4 3 2 1 0-1 -2-3 -4-5 -6-7 342 343 344 345 346 347 Mile Post Railroad ASET Figure 7: The superelevation proposed by ASET/SE versus the previous track superelevation
8 (a) (b) Figure 8: (a) Rail removed after 7-months in service. (b) Wear (reduced by 95%) over the same period after ASET recommendations were implemented
Figure 9: The superelevation proposed by ASET/SE based on a reduction in track speed versus the previous track superelevation
Figure 10: Drawbar forces versus Train Weight and Length
Figure 11: A plot of the deviation between uphill- South/Eastbound train s superelevation requirement and power ratio
Figure 12: Superelevation required by uphill-south/eastbound trains for a superelevation bandwidth of ±1 inch and power ratio of 1.5.
Figure 13: A plot of the deviation between downhill-north/westbound train s superelevation requirement and power ratio
Figure 14: Superelevation required by downhill-north/westbound trains for a superelevation bandwidth of ±1 inch and power ratio of 1.0.
Figure 15: The superelevation required by all trains in the Tehachapi under the ASET proposed train power ratio of 1.5 uphill and 1.0 downhill.