Noise Prediction Theory Model in Environmental Impact Assessment

Previously, the xuchang city planning project studied the noise pollution problem of the city, evaluated the noise of the planning scheme, and obtained the related results and treatment scheme, which is the content of environmental impact evaluation, the following is the noise model adopted by the Institute.

 

Theoretical Model of Road Traffic Noise Prediction

1.1 FHWAModel

In 1978, Barry and Reagan proposed the fhma model in the United States, which is a mathematical model for continuous highway noise prediction. Fhma divides all motor vehicles into three categories: private cars, medium trucks and heavy trucks. This paper proposes a noise level prediction formula for traffic conditions, traffic and vehicle models. FHWA splits consecutive roads into line segments. Then, based on the average noise level of each type of vehicle during normal driving conditions, FHWA first modifies the traffic volume and other traffic factors, then, the vertical distance and angle are corrected based on the map coordinates, the road condition (hard site or soft site) is determined, and the final noise level is calculated in the surrounding environment. Unlike other models, fhma focuses more on the distance and angle between the observer and the noise source.

The FHWA model is widely used at home and abroad. The noise prediction model adopted in the environmental impact assessment (Trial) of highway construction projects issued by the Ministry of Transport of China isFHWA[7]. The model consists of the following two parts:

Step 1: when a type I vehicle is traveling between the distance or at night, the hourly traffic noise value is calculated as follows:

(Larq) I= (Formula 1)

Where:

(Larq) I-type vehicles are traveling between vehicles or at night, and the Prediction point receives hourly traffic noise, dB;

Lwoi-average sound level of type I vehicles, dB;

N-the average hourly traffic volume of Inter-or nighttime vehicles of type I (calculated according to appendix B), vehicles/h;

Average speed of U-I vehicles, km/h;

T -- the prediction time of larq, where LH is used;

△L distance-the driving noise of type I vehicles, the attenuation of the distance between the primary and nighttime prediction points whose distance from the equivalent noise line is R, dB;

△L longitudinal slope-traffic noise correction caused by longitudinal slope of highway, dB;

△L longitudinal slope-traffic noise correction caused by road surface, DB.

Step 2: Calculate the traffic noise received by the prediction point between vehicles or at night as follows:

(Formula 2)

Formula medium: (larq) L, (larq) m, (larq) s -- traffic noise values received by prediction points, DB, for large, medium, and small vehicles in the middle or at night;

(Larq) Traffic: the traffic noise values of the daytime or nighttime traffic that the prediction point receives.

△L1-traffic noise correction volume caused by highway curves or limited-length road sections, dB;

△L2-traffic noise correction caused by obstacles between highway and prediction point, DB.

The FHWA model has high data requirements and is usually used for Noise Evaluation and precise analysis of current roads. It is difficult to make precise predictions on future traffic data in urban planning, therefore, this model is usually not used in the prediction and evaluation of the planning scheme. However, the reference model provided by the Ministry of Transport can be directly used to simplify the calculation process.

1.2CrtnModel

Crtn is a traffic noise model developed by the British Ministry of Transport. Like the FHWA model, crtn is also based on continuous roads, but its formula is slightly different from the FHWA model, the crtn model mainly considers the factors that affect noise generation and propagation. The basic noise level is corrected objectively, including the following two steps [8]:

The first step is to predict the baseline noise level 10 meters away from the edge of the lane Based on the traffic flow, speed, proportion of light and heavy vehicles, highway width, Highway Slope and road surface characteristics. The noisy level is the peak noisy level within a certain period of time. The calculation formula and parameters are as follows:

Baseline sound level = reference sound level + speed and vehicle model correction + road slope correction (Formula 3)

1 h reference sound level (L10) = 42. 2 + 10lg Q (assuming no heavy vehicles, vehicle speed 75 km/h) dB ()

Speed and vehicle model correction = 33lg [(V + △v) + 40 + 500/(V + △v)] + 10lg [1 + 5 p/(V + △v)] -68. 8 dB ()

Road slope correction = 0. 3g dB ()

△V = [0. 73 + (2. 3 + 1. 15 p/100) 3 P/100] 3G km/h

Formula: Q indicates the traffic flow in the prediction period, V indicates the corrected speed, P indicates the proportion of heavy vehicles, and G indicates the road slope.

The second step considers the distance attenuation, reflection, blocking, absorption, and other factors in the traffic noise propagation to predict the noise impact of a single traffic Section on a certain receiving point. The prediction formula and parameters are as follows:

Predicted sound level = baseline sound level + distance attenuation correction + Ground absorption correction + Acoustic Barrier Block Correction + sound source Finite Length correction + wall reflection correction (formula 4)

Distance Attenuation Correction =-10 × log (D/13. 5)

Ground absorption correction = x I x log (3/(D +) H <0. 75

Sound Source Finite Length correction = 10 × log (α/180)

Wall reflection correction = × (sum of reflection angles/α)

Where: D --- the vertical distance between the prediction point and the center line of the lane;

I --- soft ground vegetation coverage;

H --- vegetation height on the ground;

α --- the source angle of the prediction point.

The crtn model has lower requirements on data than the FHWA model, and its requirements and accuracy meet the noise prediction criteria of the planning scheme in urban planning, this article mainly uses the crtn model for noise prediction and evaluation analysis.