Feasibility of a Directive On-Board Locomotive Audible Warning Device

Transcription

1 Feasibility of a Directive On-Board Locomotive Audible Warning Device Noise-Con 2011 July 25, 2011 Jason Ross, P.E. Timothy Johnson Harris Miller Miller & Hanson Inc. Basant Parida & Bud Zaouk QinetiQ-NA

2 Background It is estimated that up to 9.3 million people in the U.S. may be impacted by locomotive horn noise In 2009, there were over 1,900 incidents, over 700 injuries and over 240 fatalities at highway-rail grade crossings A train horn optimized for directivity can both improve safety and reduce environmental noise impact

3 Background The National Academy of Engineering Committee on Technology for a Quieter America has indicated that the public would benefit if train horns were more directional This study sponsored by the Federal Railroad Administration builds off of existing data and research from: Amanda Rapoza (Volpe Acoustics Group) John Aurelius Amanda Keller Roger Kilmer Mike Fann AEJ Hardy Raymond Brach

4 Background The study includes: A recommended specification for an on-board locomotive audible warning device optimized for directivity Comparison of this device to standard horn systems for: Detectability Environmental noise benefit Occupational noise exposure benefit Assessment of a feasible technology for meeting optimized design (acoustic hailing devices) Implementation and cost considerations (not covered in this paper)

5 Standard Train Horn Systems Air Pressure Horns Typically mounted on the center of locomotive or on the cab roof Railroads have been moving horns to the center to reduce in-cab noise levels by about 10 db Generally omni-directional Although center-mounted horns have lower amplitudes forward of the locomotive due to acoustic shielding from the locomotive structure and highest amplitudes at +/- 45 deg FRA 49 CFR Parts 222 and 229 Final Rule on Use of Locomotive Horns at Highway-Rail Grade Crossings (2006) Regulates horn levels to 96 to 110 dba at 100 ft forward of locomotive Depending on train speed horns are typically sounded beginning 1/4-mile from the crossing until the first locomotive is entirely through the crossing

6 Optimized Train Horn Design Optimized audible warning device has the same signal as a typical standard 5-chime horn system (i.e. Nathan K-5-LA) Primary tones at 311, 370, 415, 494 and 622 Hz (D # 4, F # 4, G # 4, B 4 and D # 5) Nathan K-5-LA provides strong mid and high-frequency content which is important for detection While a frequency-varying signal such as that on emergency vehicles may increase sense of urgency and detectability, such a signal would be expected to similarly increase annoyance to abutters Changing the signal could decrease the association of the sound to a train event Although, we are investigating the potential use of secondary emergency warning signals which could be of this type of signal

7 Optimized Train Horn Design Optimized audible warning device primarily generates sound at angles needed for detectability to motorists and pedestrians and minimizes sound elsewhere Critical angle of sound generated depends on distance of train to crossing vehicle speed and critical distance for cars to stop prior to crossing For cars at 50 mph the critical distance for a car to stop is ~500 feet Narrowest angle is 42 deg (0 deg +/- 21) when train is at ¼-mile Widest angle is 198 deg (0 deg +/- 99) when first locomotive is entirely through crossing

8 Optimized Train Horn Design The directivity pattern continuously varies as function of train position Train Position Critical Angle 1/4-mile 42 deg (0 deg +/- 21) 3/16-mile 60 deg (0 deg +/- 30) 1/8-mile 84 deg (0 deg +/- 42) 1/16-mile 120 deg (0 deg + /- 60) 1st loco thru 198 deg (0 deg +/- 99) Minimizing the amplitude beyond the critical angle is important It has been assumed the directivity decreases 2/3 of a decibel per degree beyond the main beam width 10 dba down at 15 degrees 20 dba down at 30 degrees 25 dba down max 8

9 Optimized Train Horn Design Amplitude is varied according to train location Maximized at 110 dba (100 feet forward of locomotive) when the train is between 1/4 and 1/8-mile from the crossing Gradually decreases to 105 dba when the train is within 1/8-mile Less amplitude is needed when the train is closer to the receptor This slow variation in amplitude replicates a behavior of standard horn directivity patterns (more on this later) 9

10 Optimized Train Horn Design 10

11 Optimized Train Horn Design 11

12 Optimized Train Horn Design 12

13 Optimized Train Horn Design 13

14 Optimized Train Horn Design 14

15 Detectability To assess the safety of the optimized audible warning device and the standard train horns we have computed the detectability inside a typical car with windows closed, no radio and no fans for heating or cooling Levels of detectability: Audibility (d-prime = 7) Noticeability (d-prime = 17) 95% Likelihood of Noticeability (d-prime = 23.3) Detectability depends on: Horn amplitude Horn frequencies Horn directivity pattern Vehicle outdoor-to-indoor noise reduction Vehicle interior background noise Human auditory system noise

16 Detectability We have computed the total distances that certain detectability goals are met for all locations of the train within ¼-mile and for various car speeds Results for a typical standard train horn mounted at the center of a GP-40 locomotive Results are similar to time audible, but do not depend on train speed or sounding duration Detectability depends significantly on horn directivity Distance Horn is Noticeable Distance Horn is Audible Sound Level at 200 ft Distance Horn is 95% Likely to be Noticeable In fact, detectability is greatest when the critical horn angle is near +/- 45 degrees when the train is ~200 to 500 ft from the crossing rather than when the train is closest to the crossing. This is beneficial since this train position is near the critical point to avoid a head-to-head collision 16

17 Detectability The optimized audible warning device has better detectability than standard horns Detectable for longer distances than all other standard horns analyzed Higher detectability than most standard horns 17

18 Environmental Noise Benefit Noise impact has been defined as the area with an Ldn of 65 dba or greater from horn noise Takes into account the cumulative noise exposure over the entire sounding event Amplitude, duration, number, time of day of horn sounding events in a 24-hour period We modeled areas of noise impact for: 1) A typical standard horn 2) The optimized AWD with variable directivity and amplitude (105 to 110 dba) 3) AWD with variable directivity designed for maximum safety (110 dba) 4) AWD with variable directivity designed for maximum noise benefit (96 dba) 5) AWD with static directivity sufficient for maximum critical angle deg Modeling assumptions Trains at 20, 40 and 60 mph (train speed affects sounding location and duration) Assumed one train pass every hour (~ national average) Train activity in only one direction and activity in two directions SoundplanTM 18

19 Environmental Noise Benefit Noise impact from typical standard horn Pass bys in one direction 19

20 Environmental Noise Benefit Noise impact from an AWD with static directivity Pass bys in one direction 20

21 Environmental Noise Benefit Noise impact from optimized AWD Pass bys in one direction 21

22 Environmental Noise Benefit Noise impact from typical standard horn Pass bys in both directions 22

23 Environmental Noise Benefit Noise impact from optimized horn Pass bys in both directions 23

24 Environmental Noise Benefit Noise impact area reduced 57% with optimized AWD! AWD with static directivity only reduces impact by 15% A directional train horn must have variable directivity to significantly reduce impact Distances to impact can be significantly reduced near the 1/4-mile markers 24

25 Occupational Noise Exposure Benefit In-cab occupational noise exposure depends on horn mounting location: The optimized AWD would not reduce in-cab noise if mounted in the center of the locomotive since the sound directly forward is not reduced compared to standard horn The optimized AWD would provide some (~3 db) reduction if mounted on the cab roof More effective with the cab windows open since amplitudes are lower to the wayside Optimized AWD not expected to decrease in-cab noise as much as moving a standard horn from the cab roof to the center of the locomotive (~10 db) Greater reduction if optimized AWD is mounted forward of the cab since rear radiation is reduced by 25 db 25

26 Acoustic Hailing Devices (AHDs) AHDs are the most feasible existing technology to meet the design goals Typically used by military to focus verbal commands or warning signals at high amplitudes over long distances Phased array of acoustic elements (may be piezoelectric transducers) Individual sources approximately 1 to 2 feet in diameter typically have Directivity as narrow as 30 degrees at 1 khz and higher frequencies Rear radiation is 25 db down at 2 khz and higher frequencies Directivity can be varied mechanically or electronically steered (preferred) Low frequency (300 to 1,000 Hz) directivity is key design issue for train horn signal A wider device with several acoustic elements can improve low frequency directivity Photo Copyright LRAD Corporation Photo Copyright Ultra Electronics

27 Acknowledgements HMMH and QinetiQ-NA would like to acknowledge the Federal Railroad Administration for their continued support of horn noise research

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