(b) 兩種伸縮縫在超低頻2.5 Hz - 5.0 Hz之間皆會有音量較高的現象，但與其他國家容許值比較過後，發現並未超出容許值，因此對人體的影響應可忽略不計。
(c) 過去的文獻顯示，模組型伸縮縫在全頻不加權均能音量下，產生的噪音比寬齒型伸縮縫高約13.0 dB，但根據本研究結果，兩者在低頻噪音約在3.2 dB - 10.5 dB之間，可見寬齒型伸縮縫產生的低頻噪音比預期來的嚴重。
The growth of Taiwan’s economy affects the behaviors of its residents, and the quality of their life. The increase of traffic volume clearly is one of the by-products created from this growth and inevitably raises the importance of the needs of elevated highways as part of Taiwan’s transportation structure. However, heat expansion and cold contraction can cause major damages of a relatively expensive highway. To mitigate the risk, a highway is fragmented by reserving spaces for expansion joints to prevent unavoidable threatens of the Mother Nature. Nevertheless, the fragmentation of a highway causes a problem, i.e., as a vehicle drives through and bumps against the expansion joints, Low Frequency Noise was created and discounts the quality of life for drivers and the residents who live around the highway. Recent studies further prove that Low Frequency Noise created by vehicles passing through expansion joints could endanger a person’s health. Not only could it change his heart rate, respiratory rate, and the release of epinephrine, but their similar vibration frequency between the noise and human organs could result in a resonance effect.
The purpose of this research is to analyze and investigate Low Frequency Noise from vehicles passing through expansion joints of Taiwan’s elevated highways to facilitate the Taiwan authorities to regulate an appropriate highway Low Frequency Noise control standard and its improvement if necessary.
In spite of various kinds of expansion joints, the scope of this research is limited to Low Frequency Noise from vehicles passing through Finger Expansion Joints and Module Expansion Joints, for they are the major joints used in Taiwan’s elevated highways. The noises are measured based on the size of vehicles with different frequency weighting filters – linear, A-weighting scale, and C-weighting scale filters. Among them, A-weighted Equivalent Continuous Noise Level (Leq) is specifically used by Taiwan’s Noise Control Standard while 1/3 – Octave band of linear is commonly used by others. Vehicles are sized into two groups – cars and trucks. And, trucks include semi trucks, buses, and construction vehicles.
Our study affirms the following findings:
(a) The sound level generated from trucks bumping against expansion joints is worse than the sound level generated from cars. It is because the weight of trucks is out scaled of the weight of cars.
(b) Infrasound from vehicles passing through either Module or Finger Expansion Joints is higher between the range of 2.6 Hz and 5.0 Hz. But, it still falls within the tolerance level compared with other countries’ standard and has minor concern of a person’s health.
(c) Low Frequency Noise from vehicles passing through Module Expansion Joints is 3.2 dB – 10.5 dB higher than Low Frequency Noise from vehicles passing through Finger Expansion Joints. It diminishes the benefit of using Finger Expansion Joints as joints of a highway as other scholars and articles demonstrated, i.e., full-scale Leq of linear from vehicles passing through Module Expansion Joints is 13.0 dB higher than that passing through Finger Expansion Joints.
(d) Further study of Low Frequency Noise from vehicles pass through both kinds of expansion joints show no risk for cars; however, Low Frequency Noise from trucks exceeds other countries’ standard. If we use A-weighting scale filter to measure, Low Frequency Noise from trucks passing through Module Expansion Joints is still not complied with Taiwan’s Noise Control Standard while Low Frequency Noise from truck passing through Finger Expansion Joints falls within the Standard.
Upon these findings, it is recommended that if the Taiwan authorities are to establish the maximum level of Low Frequency Noise from vehicles passing through expansion joints, not only should the standard be measured with A-weighted Leq, but similar with other countries measured with 1/3 – Octave bands as well.