Traffic noise control in SMAN 5 Surabaya

The development of transportation technology is now very rapidly with increasing of number vehicles that causes a traffic jam. The location nears a crowded highway that causes a noise pollution in SMAN 5 Surabaya. Based on noise standards of Minister of Environment of Indonesia (KEP-48/MENLH/11/1996), the permitted sound pressure level in educational environments is 55 dBA. The SPL in the environment of SMAN 5 Surabaya is 87 dBA. It is necessary to design noise barrier to reduce noise. To decrease the noise level 32 dBA, it can use noise barrier with 12 m height. The most effective method is using Maekawa based on direct calculations. This method is more accurate. The other methods used in this research are graph method, double screen and Nomograph. The best material of noise barrier planning is steel with thickness 1,25 mm that decrease noise about 32,32 dBA.


Introduction
Recently, the main problem on the street is noise which caused by traffic jam. Traffic noise is the second biggest environmental problem according to WHO after air pollution and it is affecting health the most [1]. Traffic noise arises from vehicle engine (engine operation, exhaust or exhaust system). This noise can be heard up to several meters from the source of noise [2]. Frequency of this traffic noise has the same range of frequencies audible to humans, but it can impair human comfort. Traffic noise is very disturbing to the human comfort who lives near the highway. It is very disturbing not only the human comfort who lives the highway but also human activities such as such as in the office environment, hospital environment, trade and service environment, and educational environment [1]. In this case, the authors will examine the control of noise levels due to traffic to the educational environment in SMAN 5 Surabaya. Based on the traffic noise data, it can be known the noise level in the environment and evaluate the standard of noise level for the educational environment according to the regional allocation based on the Decree of Minister of Environment No. 48 / MENLH / 1996. November 25, 1996. It designs to reduce traffic noise as well as providing recommendations of some appropriate Noise Barriers.

Noise
Noise Level of traffic can be described with graph of Leq value. Leq (Equivalent Continuous Noise Level) is a specific noise value from fickle noise (fluctuating in certain time equal with steady noise level) in the same time. Leq is measured directly by integrated sound pressure level. Leq is the level of energy average from some sound level Varian. It is not direct interference measurement. Leq can be  (1) With ti as Length of time with noise Li and T as  i t = ...
To determine Leq from (Lday = Noise level in the noon) can be calculated from the equation 2 and equation 3 using (Lnight = Noise level in the night). To know the noise, exceed of noise level or not, we must determine the value of Ldn from measurement of field data. Ldn is calculated with equation 4.

Noise standard
The Indonesian Government through of the Environment Minister Decree No: 48/ MENLH/ XI/ 1996 contains noise level limit criteria in residence and educational area which have maximum noise less than 55 dBA [4].

Noise barrier.
Noise Barrier is a barrier wall or partition used to control airborne noise transmissions, where the wall is located between the source and the receiver. The function of Noise Barrier is to provide a shadow zone or area where it has a quieter noise at the receiver [3].

Maekawa method.
Maekawa method is used to reduce sound pressure level using noise barrier. Maekawa method usually uses graph method. In this method, we can determine the reduction of sound pressure level which depend on sound frequency and distance between source to barrier. In single screen barrier, path length difference can be determined from equation 5. Equation 6 shows double screen barrier [5].
Where, δ as path length difference (m), ss d distance from source to the first tip barrier(m), dsr as distance from the second tip to receiver(m), a as distance between two barriers (m), e is distance between barrier(m) and d distance between source of noise and receiver(m). Noise Reduction (NR) is the different value of sound pressure level from source to receiver. The equation of noise reduction is shown in equation 7. NR is noise reduction(dB), SPL 1 as sound pressure level of source(dB), and SP2 as sound pressure level of receiver(dB). It can be calculated using equation 8 which assumed after value of path length difference is obtained. With B is barrier attenuation (dBA), δ is path length difference (m), and λ is wave length. 2

Object measurement
The object measurement in this research is SMAN 5 Surabaya. This area is in the center traffic of

Noise Barrier Plan in SMAN 5 Surabaya
We will use the noise barrier planning several methods that will be applied in SMAN 5 Surabaya. Figure 6, we can design the noise barrier. The assumption of sound between source and receiver is same. The data of c is 10.5 m, c1 is 7.5 m, c2 is 3 m, f is 1000 Hz, v is 340 m/s, and is 0.34. So, using the equation 8, its design can reduce the noise about 32,76 dBA with the height of noise barrier about 12 meters. Meanwhile, different noise barrier design shown in Figure  7 can reduce noise about 21.19 dBA.

Double Screen Method.
It can reduce noise about 28,121 dBA shown in Figure 8 and table 1.

Graph Method.
This method can determine the barrier attenuation used Fresnel Number from equation 9. The design of noise barrier with graph method is shown in Figure 9.

Discussion
Based on measurement data of the noise near Kusumabangsa street, the highest Leq value in 00.00-01.00 is 90.42 dBA. It is caused by vehicle which through the street like truck, motorcycle, etc. In the night driver got the height speed than day because decrease volume of vehicle. So, it caused noise. Meanwhile in the noon at 14.00-15.00, it happened the lowest noise. In the other hand, on Ambengan street got the highest noise at 12.00-13.00 about 73.32 dBA. At this time, learning