Traffic noise testing and collaborative control of elevated and ground-level composite roads

2.1. Study area and data collection

In this study, the Huangsha Avenue - Inner Ring Road elevated bridge system in Guangzhou City was selected as the research object. This area is a typical urban elevated - ground composite transportation hub. Huangsha Avenue is a two-way six-lane ground road, and the Inner Ring Road elevated bridge spans over it (two-way six-lane). The vertical projections of the two overlap to form a three-dimensional noise diffusion field (Fig. 1). The basic data were obtained through on-site measurements and traffic management records.

Fig. 1Schematic diagram of the layout of measurement points on the Huangsha Avenue – Inner Ring Road elevated Bridge

The traffic flow was monitored continuously by video counting for three typical time periods (daytime peak, daytime peak, and nighttime), and the east-west two-way flow was classified and counted by small vehicles (≤ 3.5T), medium vehicles (3.5-12 t), and large vehicles (≥ 12 t) (see Tables. 1 and 2). The data showed that the night traffic volume on the elevated Inner Ring Road reached 1,514 vehicles per 20 minutes (95.3 % for small vehicles), and the proportion of large vehicles on Huangsha Avenue at night was significantly higher than that on the elevated road (6.5 % vs 0.8 %), suggesting that heavy vehicles made a significant contribution to ground noise. The elevated bridge is 8.5m above ground, with a longitudinal slope of no more than 4 percent; Ground road longitudinal slope ≤ 2 percent. The weather conditions on the test day were stable, with a temperature of 25±2 °C, humidity of 65±5 percent, and wind speed ≤ 1.5 m/s.

2.2. Construction of noise prediction models

Build a three-dimensional acoustic propagation model based on a professional noise simulation platform. Among them, the sound source model uses the British CRTN calculation specification to determine the vehicle sound power level. The intensity of noise sources for different types of vehicles is calculated according to Eq. (1):

where the base speed $v_0$ is 60 km/h, the small car coefficient $a=$28.5, $b=$30.0, the large car coefficient $a=$33.2, $b=$33.7; $∆L_{pavement}\mathrm{ }$is the asphalt pavement correction value (–1.5 dB(A)) [7].

By importing the topographic map, precisely construct the calculation domain of length × width × height = 400 m × 300 m × 50 m (Fig. 2). Set the sound reflection coefficient of the building facade at 0.8, the surface sound absorption coefficient at 0.05, and the sound propagation algorithm using the mixed mode of Ray Noise and Virtual Source to calculate the grid resolution of 1.0 m × 1.0 m.

Fig. 2Floor plan of the noise model of the Huangsha Avenue – Inner Ring Road Elevated Bridge

Five parallel monitoring points are set up along Huangsha Avenue (7.5 meters away from the curb), and 15 vertical monitoring points are set up on the facade of the adjacent Daye Metal Building (with a height of 3 meters, numbered 1L-15L), covering the monitoring height from 4.5 meters to 49.5 m.

The reliability of the model was verified using nighttime measurement data. Among them, A sound level meter (grade 1 accuracy) was used in conjunction with a calibrator, and time weighting “Fast” and frequency weighting “A” were set. Eight characteristic measurement points (5 parallel points +3 elevation points 1L/7L/15L) were selected, and three consecutive nighttime periods (22:00-06:00) were measured. The maximum LAeq at each point was taken as the verification benchmark.

The final three-dimensional model diagram is shown in Fig. 3.

2.3. Model validation

To verify the accuracy of the model, the nighttime noise measured at the measured parallel measurement points and the vertical measurement points of the building were selected for verification. The comparison tables of the noise results are shown in Tables 3 and 4.

Fig. 33D image of the noise model of the Huangsha Avenue – Inner Ring Road Elevated Bridge

As shown in the table, the calculated results fit well with the measured data as a whole, with a minimum error of 0.2 dB and a maximum error of 3.2 dB, which occurred at parallel measurement point 5.

From the measured results, it is known that the maximum noise value at the parallel measurement point at night is 76 dB(A), exceeding the limit (65 dB(A)) by 11 dB, and the minimum noise value is 72.0 dB(A), exceeding the limit (65 dB(A)) by 7dB; The maximum noise at the building measurement point was 73.4 dB, which exceeded the limit (55 dB(A)) by 18.4 dB, and the minimum noise was 68.1 dB(A), which exceeded the limit (55 dB(A)) by 13.1 dB. The measured noise at night exceeded the limit.

According to the calculation results, the maximum noise value at the parallel measurement point at night was 73.0 dB(A), which exceeded the limit (65 dB(A)) by 8 dB, and the minimum noise value was 72.7 dB(A), which exceeded the limit (65 dB(A)) by 7.7 dB. The noise levels at the measurement points were all above the limit; The maximum noise at the building measurement point at night was 73.1 dB(A), exceeding the limit (55 dB(A)) by 18.1 dB, and the minimum noise was 70.4 dB(A), exceeding the limit (55 dB(A)) by 15.4 dB.

In the case of road noise, the noise planar distribution map is shown in Fig. 4.

2.4. Design of noise reduction measures

The traffic noise on Huangsha Avenue and the elevated bridge of the Inner Ring Road is the main source of noise. Through the prediction of the selection of noise control measures, the results show that the noise in this section exceeds the standard relatively high. Huangsha Avenue may need to adopt both noise reduction pavement and sound barriers as noise reduction measures, and the Inner Ring Road needs to adopt sound barriers. A 5-meter-high sound barrier was used for Huangsha Avenue and the Inner Ring Road elevated bridge, and a porous asphalt pavement was adopted for Huangsha Avenue to increase the porosity of asphalt concrete to absorb noise, and a model was established for noise simulation calculation. The noise results after setting the noise reduction measures are shown in Fig. 5.

Fig. 4Map of the noise results of the Huangsha Avenue – Inner Ring Road Elevated Bridge

Fig. 5Map of the night noise results of the Huangsha Avenue – Inner Ring Road Elevated Bridge with noise reduction measures in place

To better compare the noise reduction effect, the predicted values of each floor of Daye Metal Building without noise reduction treatment were compared with those of Daye Metal Building with noise reduction measures, as shown in Table 5.

The results show that the sound barriers and noise-reducing pavement have a significant effect. The maximum noise reduction at each measurement point and building floor can reach 18.8 dB, and the impact on buildings is particularly significant. This indicates that noise reduction measures for elevated Bridges can greatly improve the noise impact on high-rise buildings.