Use of Track Quality Standard Deviations in Track Design and Construction David Marriott Consultant / Developer Freelance Constantin Ciobanu CEng FPWI MCIHT Principal PWay Engineer
Mea culpa slide Track Quality Measurement and Inherent Standard Deviation The design alignment is characterised by Inherent Standard Deviations, affecting the target standard values for construction. These Inherent Design Standard Deviation is proportional to the additional vehicle acceleration induced at the changes in track geometry. Any change in the vehicle lateral or vertical acceleration due to the design, is a source of oscillations quantified by the Inherent Standard Deviations. 05/03/2018 09:10 PWI TECHNICAL SEMINAR - S&C to X&Y. Use of Track Quality Standard Deviations in Track Design and Construction 2
Track Quality Standard Deviations 4 values, produced for each 1/8 mile: Worst Top 35 m Mean Top 70 m Alignment 35 m Alignment 70 m TRC SDs when calculated from the traces of the Track Recoding Car (or other track measuring vehicles) SDs when generated by other means 05/03/2018 09:10 PWI TECHNICAL SEMINAR - S&C to X&Y. Use of Track Quality Standard Deviations in Track Design and Construction 3
Track Recording Car. Measuring system Inertial Box Accelerometers Gyroscopes Accelerometers continuous output of acceleration. Double integration of acceleration continuous output of displacement. Gyroscopes recording the angular rotation. This system produces a sequence of sampled positions of each rail in 3D space. 05/03/2018 09:10 PWI TECHNICAL SEMINAR - S&C to X&Y. Use of Track Quality Standard Deviations in Track Design and Construction 4
Recording Car. Data processing On the vertical profile of null gradient and cant, the vertical track irregularities are clearly visible The exceedances can be measured Same for the horizontal alignment as long as the track is straight (no curves or transitions) 05/03/2018 09:10 PWI TECHNICAL SEMINAR - S&C to X&Y. Use of Track Quality Standard Deviations in Track Design and Construction 5
Recording Car. Data processing The real track trace requires processing to turn the raw data into meaningful information. 05/03/2018 09:10 PWI TECHNICAL SEMINAR - S&C to X&Y. Use of Track Quality Standard Deviations in Track Design and Construction 6
Filter The filter removes the long wavelength parts of the measured profile. Tuned to a specific cut-off wavelength. Shorter wavelength components will pass the filter Longer wavelength components will not pass The design vertical profile generally has a long wavelength shape whereas the irregularities we are interested in generally have short wavelength. 05/03/2018 09:10 PWI TECHNICAL SEMINAR - S&C to X&Y. Use of Track Quality Standard Deviations in Track Design and Construction 7
Filtered vertical profile Filtering 05/03/2018 09:10 PWI TECHNICAL SEMINAR - S&C to X&Y. Use of Track Quality Standard Deviations in Track Design and Construction 8
Standard Deviation SD(0/1) = 1.338 SD(0/2) = 1.403 SD(0/3) = 1.198 SD(0/4) = 1.256 SD(0/1) = 1.333 SD(0/2) = 1.276 SD(0/3) = 1.202 SD(0/4) = 1.564 the roughness of the track trace. SD = σ n i=1 z i z 2 m n 1 Standard Deviation is used to express 05/03/2018 09:10 PWI TECHNICAL SEMINAR - S&C to X&Y. Use of Track Quality Standard Deviations in Track Design and Construction 9
Choice of filter and cut-off wavelength 4-pole Butterworth filter is used to process the recorded measurements. Short cut-off wavelength: 35 m UK; 25 m for other UIC members Long cut-off wavelength: 70 m Waveband Phenomenon Remedy 1-30 cm Corrugation Rail grinding 1-100 cm Poor weld geometry Rail bending 1-3 m Poor wheel treads Wheel tread turning 2-3 m Rolling defects Grinding up to 2 m 3-35 m Moderatelly long waves Automatic tamping 35-70 m Long waves Design tamping 70 - m Geometric design Design tamping 05/03/2018 09:10 PWI TECHNICAL SEMINAR - S&C to X&Y. Use of Track Quality Standard Deviations in Track Design and Construction 10
Interpretation of TRC SDs The SDs were initially used to indicate the general level of roughness of the track. For each track category the quality bands were defined as: good satisfactory poor very poor For a particular 1/8 mile, an SD value increasing from one recording run to the next indicated a section of track with deteriorating track quality. A different interpretation A recorded SD of a particular parameter for a particular 1/8 mile was in the "poor" band was taken to indicate that track quality of that 1/8 was "poor. It is not true to say that the value of an 1/8 mile SD is always an absolute measure of track quality. Construction Standards SD specification for track construction was introduced: the "as built" track should have TRC SDs which are in the "good" band for the relevant track category. 05/03/2018 09:10 PWI TECHNICAL SEMINAR - S&C to X&Y. Use of Track Quality Standard Deviations in Track Design and Construction 11
Effect of Geometrical Design on Filtered Profile Changing scale 05/03/2018 09:10 PWI TECHNICAL SEMINAR - S&C to X&Y. Use of Track Quality Standard Deviations in Track Design and Construction 12
Design (Inherent) Standard Deviation SD(0/1) = 0.418 SD(0/2) = 0.649 SD(0/3) = 0.556 SD(0/4) = 0.586 SD(0/1) = 0.429 SD(0/2) = 0.479 SD(0/3) = 0.488 SD(0/4) = 0.432 Not all the SDs of the filtered alignment are zero! 05/03/2018 09:10 PWI TECHNICAL SEMINAR - S&C to X&Y. Use of Track Quality Standard Deviations in Track Design and Construction 13
Filter behaviour Input a cosine wave Shorter wavelength components will pass the filter Longer wavelength components will not pass 05/03/2018 09:10 PWI TECHNICAL SEMINAR - S&C to X&Y. Use of Track Quality Standard Deviations in Track Design and Construction 14
Frequency response 05/03/2018 09:10 PWI TECHNICAL SEMINAR - S&C to X&Y. Use of Track Quality Standard Deviations in Track Design and Construction 15
Design elements continuous vertical gradient Filtering 05/03/2018 09:10 PWI TECHNICAL SEMINAR - S&C to X&Y. Use of Track Quality Standard Deviations in Track Design and Construction 16
Design elements continuous vertical curve Filtering 05/03/2018 09:10 PWI TECHNICAL SEMINAR - S&C to X&Y. Use of Track Quality Standard Deviations in Track Design and Construction 17
Design elements Gradient change Filtering 05/03/2018 09:10 PWI TECHNICAL SEMINAR - S&C to X&Y. Use of Track Quality Standard Deviations in Track Design and Construction 18
Design elements Vertical curve Filtering 05/03/2018 09:10 PWI TECHNICAL SEMINAR - S&C to X&Y. Use of Track Quality Standard Deviations in Track Design and Construction 19
Design elements Curvature changes Filtering 05/03/2018 09:10 PWI TECHNICAL SEMINAR - S&C to X&Y. Use of Track Quality Standard Deviations in Track Design and Construction 20
Design elements Cant changes Filtering 05/03/2018 09:10 PWI TECHNICAL SEMINAR - S&C to X&Y. Use of Track Quality Standard Deviations in Track Design and Construction 21
Filter Artefacts. Mercator projection North Pole Equator L = 24 900 miles South Pole 05/03/2018 09:10 PWI TECHNICAL SEMINAR - S&C to X&Y. Use of Track Quality Standard Deviations in Track Design and Construction 22
The TGSD Calculator A software to compute the SDs produced by the TRC measuring the design geometry a perfect track, without irregularities. Validated independently by modelling Recording Car. Revised Construction Standards The TGSD Calculator is computing the SDs of artefacts of the TRC filtering. 05/03/2018 09:10 PWI TECHNICAL SEMINAR - S&C to X&Y. Use of Track Quality Standard Deviations in Track Design and Construction 23
Measured against filtered design trace - 1 New S&C Old S&C to be removed Bearing change Transition Compound Transition curve 05/03/2018 09:10 PWI TECHNICAL SEMINAR - S&C to X&Y. Use of Track Quality Standard Deviations in Track Design and Construction 24
Measured against filtered design trace - 2 TRC AL70 6.569 1.801 5.020 1.476 3.165 4.062 2.055 3.483 2.971 0.801 05/03/2018 09:10 PWI TECHNICAL SEMINAR - S&C to X&Y. Use of Track Quality Standard Deviations in Track Design and Construction 25
Measured against filtered design trace - 3 Design AL70 0.000 0.000 0.000 0.367 1.542 3.522 0.875 3.780 2.840 0.000 TRC AL70 6.569 1.801 5.020 1.476 3.165 4.062 2.055 3.483 2.971 0.801 05/03/2018 09:10 PWI TECHNICAL SEMINAR - S&C to X&Y. Use of Track Quality Standard Deviations in Track Design and Construction 26
Measured against filtered design trace - 4 Design AL70 0.000 0.000 0.000 0.367 1.542 3.522 0.875 3.780 2.840 0.000 TRC AL70 6.388 1.653 1.064 2.729 2.793 2.957 2.170 4.569 2.711 0.728 05/03/2018 09:10 PWI TECHNICAL SEMINAR - S&C to X&Y. Use of Track Quality Standard Deviations in Track Design and Construction 27
Case study 1 Sudden drop in vertical profile (an extreme illustrative example) A design vertical profile with a sudden drop of 1.8 m 1.8 m when filtered to a cut off wavelength of 70 m will give a MT70 SD of 0.242 mm The SD of the filtered design profile is not an indication of the design track quality! MT70 SD = 0.242 05/03/2018 09:10 PWI TECHNICAL SEMINAR - S&C to X&Y. Use of Track Quality Standard Deviations in Track Design and Construction 28
Case study 2a Negative cant V Radius E D Transition RgE RgD mph m mm mm m mm/s mm/s 0.000 0 0.0 100 53.7 34.0 80 800.000 150 94.9 100 53.7 34.0 0.000 0 0.0 WT35 = 0.724 MT70 = 1.043 05/03/2018 09:10 PWI TECHNICAL SEMINAR - S&C to X&Y. Use of Track Quality Standard Deviations in Track Design and Construction 29
Case study 2a Negative cant V Radius E D Transition RgE RgD mph m mm mm m mm/s mm/s 0.000 0 0.0 100 53.7 34.0 80 800.000 150 94.9 100 53.7 34.0 0.000 0 0.0 WT35 = 0.724 MT70 = 1.043 V Radius E D Transition RgE RgD mph m mm mm m mm/s mm/s 0.000 0 0.0 100 53.7 141.3 80 800.000-150 394.9 100 53.7 141.3 0.000 0 0.0 WT35 = 0.724 MT70 = 1.043 Negative cant, when passed through the filter, will leave a similar artefact as the normal cant. 05/03/2018 09:12 PWI TECHNICAL SEMINAR - S&C to X&Y. Use of Track Quality Standard Deviations in Track Design and Construction 30
Case study 2b Removing cant V Radius E D Transition RgE RgD mph m mm mm m mm/s mm/s 0.000 0 0.0 100 53.7 34.0 80 800.000 150 94.9 100 53.7 34.0 0.000 0 0.0 WT35 = 0.724 MT70 = 1.043 V Radius E D Transition RgE RgD mph m mm mm m mm/s mm/s 0.000 0 0.0 100 0.0 87.6 80 800.000 0 244.9 100 0.0 87.6 0.000 0 0.0 WT35 = 0.000 MT70 = 0.000 If the cant is removed the Design Vertical SDs are lower. Is the design track quality better if we remove cant? 05/03/2018 09:10 PWI TECHNICAL SEMINAR - S&C to X&Y. Use of Track Quality Standard Deviations in Track Design and Construction 31
Case study 3 Longer design elements Technically compliant and best fit alignment V Radius E D Transition RgE RgD Eg mph m mm mm m mm/s mm/s 1 IN 0.000 0 0.0 80 70 51.1 51.1 700 980.000 100 99.9 AL70 Filtered design alignment SD = 3.845 Should the design alignment be changed? 05/03/2018 09:10 PWI TECHNICAL SEMINAR - S&C to X&Y. Use of Track Quality Standard Deviations in Track Design and Construction 32
Case study 3 Longer design elements Technically compliant and best fit alignment V Radius E D Transition RgE RgD Eg mph m mm mm m mm/s mm/s 1 IN 0.000 0 0.0 80 70 51.1 51.1 700 980.000 100 99.9 Filtered design alignment AL70 SD = 3.845 Second iteration Bring AL70 SD is below 1.7 V Radius E D Transition RgE RgD Eg mph m mm mm m mm/s mm/s 1 IN First iteration bring RgE and RgD below 35mm/s (Normal Design Limit) V Radius E D Transition RgE RgD Eg mph m mm mm m mm/s mm/s 1 IN 0.000 0 0.0 80 105 34.1 34.1 1050 980.000 100 99.9 Filtered design alignment AL70 SD = 2.541 0.000 0 0.0 80 160 22.4 22.4 1600 980.000 100 99.9 Filtered design alignment AL70 SD = 1.656 05/03/2018 09:10 PWI TECHNICAL SEMINAR - S&C to X&Y. Use of Track Quality Standard Deviations in Track Design and Construction 33
Case study 3 Longer design elements Technically compliant and best fit alignment V Radius E D Transition RgE RgD Eg mph m mm mm m mm/s mm/s 1 IN 0.000 0 0.0 80 70 51.1 51.1 700 980.000 100 99.9 Filtered design alignment AL70 SD = 3.845 Is this last design (Lt = 160 m) better? From the point of view of the rates of change for cant and cant deficiency, YES. The AL70 SD is indeed lower. However, the SD of the filtering residues is not an indicator of the design track quality. Longer alignment elements are preferred for a good design. V Radius E D Transition RgE RgD Eg mph m mm mm m mm/s mm/s 1 IN 0.000 0 0.0 80 160 22.4 22.4 1600 980.000 100 99.9 Filtered design alignment AL70 SD = 1.656 Longer alignment elements, when filtered using the TGSD Calculator, will most probably produce lower Design SDs. Can the better design be installed? A 900 mm shift (slew) is required throughout the entire circular curve to install the 160 m clothoid transition. 05/03/2018 09:10 PWI TECHNICAL SEMINAR - S&C to X&Y. Use of Track Quality Standard Deviations in Track Design and Construction 34
Case study 4 math operations with SDs V Radius E D Transition RgE RgD Eg mph m mm mm m mm/s mm/s 1 IN 0.000 0 0.0 80 70 51.1 51.1 700 980.000 100 99.9 Filtered design alignment AL70 SD = 3.845 Case 4.1 AL 70 SD (mm) SD difference TRC Trace 4.27 0.44 Design Alignment 3.84 Track irregularities 1.91 05/03/2018 09:10 PWI TECHNICAL SEMINAR - S&C to X&Y. Use of Track Quality Standard Deviations in Track Design and Construction 35
Case study 4 math operations with SDs V Radius E D Transition RgE RgD Eg mph m mm mm m mm/s mm/s 1 IN 0.000 0 0.0 80 70 51.1 51.1 700 980.000 100 99.9 Filtered design alignment AL70 SD = 3.845 Case 4.1 AL 70 SD (mm) SD difference TRC Trace 4.27 0.44 Design Alignment 3.84 Track irregularities 1.91 SD(x i ) = σ n i=1 x i x m 2 n 1 SD(x i ) SD(y i ) SD(x i y i ) 05/03/2018 09:10 PWI TECHNICAL SEMINAR - S&C to X&Y. Use of Track Quality Standard Deviations in Track Design and Construction 36
Case study 4 SD math operations SD(x i ) SD(y i ) SD(x i y i ) No other simple mathematical operation works on SD By filtering the recorded track shape which includes the design geometry we are blinded to the real amplitude of track irregularities. The actual track quality cannot be accurately predicted. Neither its deterioration. Case 4.1 AL 70 SD (mm) SD difference TRC Trace 4.27 Design Alignment 3.84 0.44 Track irregularities 1.91 Case 4.2 AL 70 SD (mm) SD difference TRC Trace 4.77 Design Alignment 3.84 0.93 Track irregularities 3.24 Case 4.3 AL 70 SD (mm) SD difference TRC Trace 4.88 Design Alignment 3.84 1.04 Track irregularities 1.86 05/03/2018 09:10 PWI TECHNICAL SEMINAR - S&C to X&Y. Use of Track Quality Standard Deviations in Track Design and Construction 37
What else can we do? 1. Review the rate of deterioration of the SD from one measurement to the next 2. Subtract the design artefact from the recorded trace This happens in sections of track where the effect of the filter artefacts is significant. The most significant influence is for alignments designed for 80-90 mph, where the AL70 and MT70 filtered design artefact can generate quite significant SD values. 05/03/2018 09:10 PWI TECHNICAL SEMINAR - S&C to X&Y. Use of Track Quality Standard Deviations in Track Design and Construction 38
Conclusions The design alignment is not entirely filtered out from the TRC traces (AL35, AL70, WT35, MT70). The Butterworth filter, used in this process, leaves in the traces artefacts at any change in design geometry. These artefact do not exist on track. They, however, can influence the SDs calculated by the TRC. Because TRC SDs are not an absolute measure of track quality, a large SD does not necessarily represent a large track irregularity when large TRC are present maintenance resources could be wasted attempting to correct irregularities that don t actually exist? 05/03/2018 09:10 PWI TECHNICAL SEMINAR - S&C to X&Y. Use of Track Quality Standard Deviations in Track Design and Construction 39
Conclusions The TGSD Calculator, a tool developed in 2007 by David C. Marriott, calculates the Standard Deviations for the Design Alignment filtered through the 4 pole Butterworth filter. The Standard Deviations calculated using this software should not be subtracted or added from/to standard limits to evaluate the (Track Quality) Standard Deviations calculated by the TRC. The Design Alignment Standard Deviations calculated using this software are not closely related to the quality of the design or of the installed track. They are not based on dynamic modelling nor on evaluating the vehicle accelerations. Therefore these SD values should not be used as a measure of the design quality or installation. 05/03/2018 09:10 PWI TECHNICAL SEMINAR - S&C to X&Y. Use of Track Quality Standard Deviations in Track Design and Construction 40
References: GC/EH0038 (1993) Track Recording Handbook. British Railway Board Raymond Lewis (2011) Track Geometry Recording and Usage. Notes for a lecture to Network Rail. TR-DOS-38 (1986) Passenger comfort during high speed curving. Summary report. British Rail Research. Coenraad Esveld (2001) Modern Railway Track. MRT Productions NR/L2/TRL/2102 (2016) Design and Construction of Track. Issue 8. Network Rail. NR/L2/TRL/001/mod11 (2012) Track geometry Inspections and minimum actions. Issue 6. Network Rail. VTI notat 56A (2003) UIC comfort tests. Investigation of ride comfort and comfort disturbance on transition and circular curves. UIC - International Union of Railways BS EN 13848-6:2014. Railway applications - Track - Track geometry quality. Part 6: Characterisation of track geometry quality. CEN. British Standards Institution. David Marriott (2007) Track Geometry SD Calculator v 1.1. User s Guide. Contact details: David Marriott mail@davidcm.com Constantin Ciobanu Constantin.Ciobanu@atkinsglobal.com 05/03/2018 09:10 PWI TECHNICAL SEMINAR - S&C to X&Y. Use of Track Quality Standard Deviations in Track Design and Construction 41
Thank you! 05/03/2018 09:10 PWI TECHNICAL SEMINAR - S&C to X&Y. Use of Track Quality Standard Deviations in Track Design and Construction 42