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APPENDIX A VEHICLE NOISE EMISSIONS
This appendix contains noise-emission equations and graphs for the five built-in vehicle types within FHWA TNM®:
- Automobiles: all vehicles having two axles and four tires - designated primarily for transportation of nine or fewer passengers, i.e., automobiles, or for transportation of cargo, i.e., light trucks. Generally, the gross vehicle weight is less than 4500 kg (9900 lb).
- Medium trucks: all cargo vehicles with two axles and six tires. Generally, the gross vehicle weight is greater than 4,500 kg (9,900 lb), but less than 12,000 kg (26,400 lb).
- Heavy trucks: all cargo vehicles with three or more axle. Generally, the gross vehicle weight is greater than 12,000 kg (26,400 lb).
- Buses: all vehicles having two or three axles and designated for transportation of nine or more passengers
- Motorcycles: all vehicles with two or three tires with an open-air driver and/or passenger compartment.
For each vehicle type, this appendix contains equations for the following components of sound-level emissions:
- A-weighted sound-level emissions
- 1/3rd-octave-band spectra, relative to A-weighted sound-level emissions
- Vertical subsource strengths, relative to 1/3rd-octave-band spectra.
In addition, this appendix describes how user-defined vehicles merge with TNM's built-in noise-emission equations.
A.1 Overview
As a single vehicle passes by a microphone 15 meters (50 feet) to the side, its sound level rises, reaches a maximum, and then falls as the vehicle recedes down the roadway. The maximum A-weighted sound level during the passby is called that vehicle's noise-emission level.
Measurement of vehicle noise-emission levels for TNM are reported separately [Fleming 1995]. These TNM emission-level measurements were confined to relatively flat ground, with the microphone at height 1.5 meters (5 feet) and horizontal distance 15 meters (50 feet). Generally the ground between the roadway edge and the microphone was acoustically absorptive, although not always. At the moment of maximum A-weighted sound level, the vehicle's 1/3rd-octave-band spectrum was also measured at the microphone. This spectrum, relative to the A-weighted sound level, is called the vehicle's noise-emission spectrum.
Measurement of vertical subsources for TNM are also reported separately [Coulson 1996]. These subsource measurements were also confined to relatively flat ground, with an array of microphone heights at horizontal distance 7.5 meters (25 feet). For these measurements, the ground between the roadway edge and the microphone array was acoustically hard, although the data were analyzed to subtract out the effects of ground reflections.
This appendix describes the results of all TNM emission-level measurements and their statistical analysis.
A.2 Definition of Variables
To calculate sound levels for entire traffic streams, TNM must incorporate energy-average vehicle noise emissions for each vehicle type. These energy-average emission levels depend upon the following variables:
f nominal 1/3rd-octave-band center frequency, in Hz
i index over vehicle types: built-in types and user-defined types
p index over pavement types:
- Average (of DGAC and PCC)
- DGAC (dense-graded asphaltic concrete), often called asphalt
- PCC (Portland cement concrete), often called concrete
- OGAC (open-graded asphaltic concrete).
s vehicle speed, in kilometers per hour. Speed varies with roadway segment. It may also vary by vehicle type, either because the user enters a different input speed or because TNM internally calculates speed due to upgrades or traffic-control devices (see Appendix B).
A.3 A-weighted Noise-Level Emissions and 1/3rd-Octave-Band Spectra, as Measured
TNM needs three constants to compute A-weighted noise-level emissions: A, B and C. In addition, it needs fourteen additional constants to convert these A-weighted noise-level emissions to 1/3rd-octave-band spectra: D1 , D2 , E1 , E2 , F1 , F2 , G1 , G2 , H1 , H2 , I1 , I2 , J1 and J2.
These seventeen constants depend upon two variables, i and p (vehicle type and pavement type, respectively), plus whether the vehicle is full throttle or not. Vehicles are full throttle when they accelerate away from traffic-control devices, until they reach the user's input speed. In addition, heavy trucks are full throttle on upgrades equal to 1.5 percent or more, until later level grades and downgrades allow them to accelerate back up to the user's input speed.
A.3.1 Built-in vehicle types
Table 5 contains the required seventeen constants, for all combinations of vehicle type, pavement type, and throttle condition.
For any roadway/traffic situation, the pavement type and throttle condition will be known. The traffic will include several different vehicle types, i, each with its own speed, si . For these emission calculations, TNM substitutes the relevant constants from Table 5 into the following set of equations, to determine each vehicle type's total measured noise emissions:
where speed, s, is in kilometers per hour and "Log10" denotes the common logarithm (base 10).
The first of these equations yields the energy form, EA , of the maximum passby A-weighted sound level for the vehicle type. The second equation converts this EA to a 1/3rd-octave--band spectrum. This spectrum is also A-weighted, because each of its measured one-third -octave-band levels has been A-weighted. Therefore, when the energies are added for each frequency band, using the equation for Lemis, i (s i, f ), the sum, converted to a level, is the A-weighted sound level, without need for further A-weighting. The third equation converts these 1/3rd-octave-band levels to their energy form.
This set of equations determines each built-in vehicle type's energy-mean emission spectrum, as measured during individual vehicle passbys at 15 meters (50 feet) over flat, generally absorptive terrain.
A.3.2 User-defined vehicle types
Subject to FHWA policy guidelines, TNM allows user-defined vehicle types to supplement its built-in vehicle types.
FHWA provides specific instructions in [Lee 1997] for the required field measurements and data analysis. In brief, each vehicle type's A-weighted emission levels must be measured in the field, as a function of speed, and then energy-mean emissions must be regressed against vehicle speed. This regression yields the three vehicle-emission constants: A, B and C. Next the resulting constant B must be converted into the vehicle's energy-mean emissions at 80 kilometers per hour (50 miles per hour), which the user enters along with A and C into TNM's traffic dialog box for user-defined vehicles.
Through this process, TNM incorporates customized A-weighted sound-level emissions for user-defined vehicles. For the user-defined vehicle type, TNM substitutes the spectrum constants (D through J) for whichever built-in vehicle the user designates as most similar, again in the traffic dialog box.
A.4 Vertical Subsources, as Measured
TNM needs five additional constants to compute vertical subsource vehicle emissions: L, M, N, P and Q. These constants also depend upon the two variables, i and p, plus throttle condition.
A.4.1 Built-in vehicle types
Table 6 contains the measured values of these five constants, for all combinations of vehicle type, pavement type, and throttle condition.
For any roadway/traffic situation, the pavement type and throttle condition will be known. The traffic will include several different vehicle types, i, each with its own speed, si. For this calculation, TNM then substitutes the relevant five constants from Table 6 into the following equation, to determine the subsource-split ratio, ri :
Note that the frequency, f, appears explicitly in this equation and also that the equation isindependent of vehicle speed, si. In this equation, r is the ratio of upper-height to lower height energy spectra. Intuitively, one might expect the subsource height split to be a function of vehicle speed, e.g., as speed increases, the split should be more heavily weighted towards the lower height because of the increased effect of tire/road noise. The current subsource height database contains limited data at low speeds (less than 30 mph). If additional subsource height data is obtained at low speeds, it is expected that the above equation would need to be modified to take into account vehicle speed.
TNM next combines these ratios, ri , with each vehicle type's total measured emissions from the previous section, to split its total emissions into vertical subsources:
Physically, this last equation represents each vehicle type's energy-mean emission spectrum, split into its two vertical subsources, as measured during individual vehicle passbys at 15 meters (50 feet) over flat, generally absorptive terrain. Note that L, M, N, P, and Q were obtained by regression from data at 7.5 meters (25 feet) over flat hard terrain. However, these data were analyzed in a manner that subtracts out the effect of the hard terrain and makes their use here, in this manner, legitimate.
A.4.2 User-defined vehicles
For a user-defined vehicle, TNM substitutes the subsource heights for the built-in vehicle that the user designates as most similar. Table 6 mentions this substitution in the appropriate column heading.
A.5 Vertical Subsources, Free Field
Next TNM eliminates the ground effects within these measured vehicle emissions. To do this, it multiplies each measured vertical subsource emission by the values in Table 7.
Mathematically:
The subscripts, ff, stand for free field. Physically, this last equation represents each vehicle type's measured energy-mean emission spectrum, as if the vehicles passed by during measurements at 15 meters (50 feet) without any intervening ground (that is, free field).
| Freq (Hz) | 800 | 1000 | 1250 | 1600 | 2000 | 2500 | 3150 | 4000 | 5000 | 6300 | 8000 | 10000 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Multiplier m, Height: 3.66m | 1.00 | 1.00 | 1.00 | 1.00 | 1.00 | 1.00 | 1.00 | 1.00 | 1.00 | 1.00 | 1.00 | 1.00 |
| Multiplier m, Height: 1.55m | 1.00 | 1.00 | 1.00 | 1.00 | 1.00 | 1.00 | 1.00 | 1.00 | 1.00 | 1.00 | 1.00 | 1.00 |
| Multiplier m, Height: zero | 0.56 | 0.54 | 0.49 | 0.42 | 0.35 | 0.30 | 0.25 | 0.22 | 0.21 | 0.21 | 0.3 | 0.36 |
These values were derived by using propagation algorithms of TNM to determine the effect of the (absorptive) ground present during the emission-level measurements.
A.6 Plots of All Noise Emissions
Figure 6 shows A-weighted sound-level emissions for TNM's built-in vehicle types, for average pavement and cruise throttle. The following figures plot all noise emissions, separately by vehicle type and throttle condition (cruise or full):
- Figures 7 through 16: A-weighted sound-level emissions
- Figures 17 through 32: emission spectra, separately by pavement type
- Figures 33 through 40: high/low energy split.
Figure 6. A-weighted sound-level emissions: Average pavement, cruise throttle.
Figure 7. A-weighted sound-level emissions: Automobiles, cruise throttle.
Figure 8. A-weighted sound-level emissions: Automobiles, full throttle.
Figure 9. A-weighted sound-level emissions: Medium trucks, cruise throttle.
Figure 10. A-weighted sound-level emissions: Medium trucks, full throttle.
Figure 11. A-weighted sound-level emissions: Heavy trucks, cruise throttle.
Figure 12. A-weighted sound-level emissions: Heavy trucks, full throttle
Figure 13. A-weighted sound-level emissions: Buses, cruise throttle
Figure 14. A-weighted sound-level emissions: Buses, full throttle
Figure 15. A-weighted sound-level emissions: Motorcycles, cruise throttle
Figure 16. A-weighted sound-level emissions: Motorcycles, full throttle
Figure 17. Emission spectra: Automobiles, average pavement
Figure 18. Emission spectra: Automobiles, DGAC pavement
Figure 19. Emission spectra: Automobiles, OGAC pavement
Figure 20. Emission spectra: Automobiles, PCC pavement
Figure 21. Emission spectra: Medium Trucks, Full Throttle
Figure 22. Emission spectra: Medium Trucks, Cruise, throttle, average pavement
Figure 23. Emission spectra: Medium Trucks, Cruise, throttle, DGAC pavement
Figure 24. Emission spectra: Medium Trucks, Cruise, throttle, OGAC pavement
Figure 25. Emission spectra: Medium Trucks, Cruise, throttle, PCC pavement
Figure 26. Emission Spectra: Heavy Trucks, full throttle
Figure 27. Emission Spectra: Heavy Trucks, cruise throttle, average pavement
Figure 28. Emission Spectra: Heavy Trucks, cruise throttle, DGAC pavement
Figure 29. Emission Spectra: Heavy Trucks, cruise throttle, OGAC pavement
Figure 30. Emission Spectra: Heavy Trucks, cruise throttle, PCC pavement
Figure 31. Emission Spectra: Buses
Figure 32. Emission Spectra: Motorcycles
Figure 33. Sound emissions, high/low energy split: Automobiles
Figure 34. Sound emissions, high/low energy split: Medium trucks, cruise throttle
Figure 35. Sound emissions, high/low energy split: Medium trucks, full throttle
Figure 36. Sound emissions, high/low energy split: Heavy trucks, cruise throttle
Figure 37. Sound emissions, high/low energy split: Heavy trucks, full throttle
Figure 38. Sound emissions, high/low energy split: Buses, cruise throttle
Figure 39. Sound emissions, high/low energy split: Buses, full throttle
Figure 40. Sound emissions, high/low energy split: Motorcycles
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