The effect of noise on the comfort of passengers inside the tramway and its impact on traffic congestion in the urban area

1. Introduction

In recent years, there has been an increasing interest in environmental noise, particularly noise caused by the different means of transport [1-3]. It’s a severe problem, because it has negative impacts on the humans' health [4, 5]. Several factors cause the noise in the urban environment, among these sources, road traffic, trains and certainly the tramways [5, 6].

Many studies have focused on the noise caused by the tramway, because it is a cause of nuisance for urban population [5, 7-13]. In addition, huge efforts are made by the tram manufacturers to lower this factor inside and outside the vehicle [14].

The tramways are widely used to relieve congestion in urban area. This contributes to decrease the noise of vehicles in neighboring homes and to reduce CO2 emissions [15, 16], and that what have led to the restoration of trams around the world [17]. However, the comfort of passengers is strongly affected by the noise inside the tram [18]. It is a source of annoyance not only for the inhabitants [19-21] but also for users. For this reason, it’s necessary to decrease the level of noise inside the tramway and in the neighboring of railways [22].

Furthermore, it's important to predict the future noise levels [23] and to take into account this constraint during the construction of new lines of the tram in cities [24]. That will encourage people to use the tramway more than their particular cars because the tram will be more efficient and comfortable. This will help to reduce congestion and accidents in the urban areas [25].

This paper will focus on the annoyance caused by the noise inside tramway. The aim of This investigation is to determine the noise and to analyze the factors that cause it inside every cabin of the tram and along the tram line. This work also shows the opinion of passengers about this noise, its effect on their comfort and on their mode choice of transportation.

2. The case study

This section introduces the area of study and presents the problems relate to the operation of tramway. In addition, to show the impact of this last on the road traffic and its effect on the level of noise inside tramway and in city.

3. Architecture of the tram and characteristic

In order to reduce the noise and make the tramway more comfortable, new trams are developed with low-floor and with auxiliary materials on the roof [30]. The proposed vehicle is from the CITADIS range, under reference Alstom CITADIS 402, its type is 100 % low-floor, it is 75 % motorized vehicle and it has a total capacity of 302 passengers.

The vehicle is bidirectional and it is expected to operate as a single unit. The tram is composed of seven articulated sections. The base vehicle Alstom CITADIS 402 includes the following modules:

• 2 motorized cabin (M1 et M2);

• 1 motorized nacelle (NM) and 1 carrier nacelle(NP);

• 3 suspended central section (cars-bodies) (C1, C2 and CC) [31].

Fig. 3Architecture of Constantine’s tramway

The vehicle section is curved to the radius of 10 meters. The external width is 2650 mm to optimize the constraints of maintain and comfort in the right seats and interior width of 2.490 m. The length of the vehicle is 43.763 meters; this value is likely to change very slightly with the finalization of the cabin aesthetics. The proposed width, combined with the length of the vehicle, enables an important capacity and offer comfort to passengers.

The Constantine’s tramway contains 4 bogies which are three motorized bogies and one bogie carrier. The motor is a three-phase asynchronous squirrel cage [31].

4. Track conception criteria

In urban areas, the rails used in Constantine are mainly grooved rails, in order to be drowned

in the roadway. The excitement wheel rail is among the major sources of noise and vibration inside the tram. The track design is based on the following constraints:

• Users comfort, security of passenger, level of noise and vibration;

• Maximum speed along the track layout;

• Simple construction and Simple maintenance [32].

The features of the soil and track play major role in the degree of noise and vibration [33]

5. Traction system

The traction system of tram includes:

• The socket by pantograph bow fitted with carbon bands;

• The protector;

• The main circuit breaker (DJ) that puts all the equipment under voltage but opens automatically in case of short circuit to protect the rest of the components;

• The static converter (CVS) which can produce from 750 V;

• The contact line, three-phase alternating voltages or continuous, variable amplitude;

• The traction motors;

• The return brushes of the line current and setting the potential of rail vehicles, each of these functions being provided by separate devices housed in the wheels [34].

Fig. 5System of traction energy of Constantine tramway

6. The noise measurements inside the tram

6.3. The results of experimental measurement step

The graphs below represent the noise measurements inside the seven tram cabs in both directions of the line. The first itinerary is from Zouaghi Slimane station to Benabdelmalek station, and the second one is from Benabdelmalek station to Zouaghi Slimane station.

We notice that the cabins with bogies make more noise than suspended central sections (C1, CC and C2). On several sections of the line, the noise is higher than the minimum and maximum values measured inside the tram before its official operation. The source of the noise in the curves and in sections which contain many stations is mainly associated to the bogies and the auxiliary equipment on the roof. The tram passes in these sections in both directions with a low velocity between 7 km/h and 30 km/h. The noise in these sections is between 65 dB(A) and 79 dB(A).

The second source of noise is related to the wheel-rail contact. It’s detected when the velocity is between 40 km/h and 60 km/h. This noise is very high and it happens in some sections in both directions at 83.1 dB(A). Many trams have a loud noise that has reached 88. 9 dB(A), this value is very elevated for a new Citadis tramway. From here, it was noticed that the noise in the interior of the tram increases proportionally with its velocity.

The graph shows that the section between the third kilometer, the fifth kilometer and the first kilometer section for itinerary 1 (the last kilometer section for itinerary 2) are those sections that contain a very high noise level. These are the sections that disturb the passengers of the tramways in both itineraries. The measures below were carried out at the presence of the passengers. These last were silent during the measurements. Some other experiments were done when passengers behave normally. The result shows an increase of the noise between 5-10 dB(A) and 15 dB(A) in the most critical situation. This increase doesn’t only depend on the number of the passengers inside the tram, but also of their behavior inside the tram.

In addition, when the number of passengers increases, the number of tram operating along the line increases. Otherwise, the number of trams is constant. For a high average of 18500 passengers per day, the trams are used every 3 minutes and every 5 minutes. We notice that the supply was three times higher than the demand. Therefore, this exploitation will degrade rapidly the lifetime of railway and also the rolling stock. This issue will cause a bad contact between the wheel-rail and the noise will increase.

Finally, there is another source of the noise inside the tramway, which is the sound of the passenger information system. This sound is very strong because it reaches 99 dB(A), it is repeated during 1 minute for each station.

Fig. 6Noise measurements of itinerary 1 and itinerary 2 for the cab M 1

Fig. 7Noise measurements of itinerary 1 and itinerary 2 for the cab C 1

Fig. 8Noise measurements of itinerary 1 and itinerary 2 for the cab NM

Fig. 9Noise measurements of itinerary 1 and itinerary 2 for the cab CC

Fig. 10Noise measurements of itinerary 1 and itinerary 2 for the cab NP

Fig. 11Noise measurements of itinerary 1 and itinerary 2 for the cab C2

Fig. 12Noise measurements of itinerary 1 and itinerary 2 for the cab M2

7. Survey results

This survey is made to know if the detected noise at the sections along the line and in different cabs of the tram affects the comfort of passengers or not. It was conducted in December 2016 at several times of the day. So, a random sample of 250 passengers was selected inside the tram and in its stations. Nearly the half of users of the tram, men and women of all age categories, admit that they are disturbed by the noise of friction caused by the contact between the wheel and the rail since it can last for 30 seconds in some sections; and the noise made by equipment of the roof of the cabins when the tram crosses some curves.

Fig. 13 represents the response of the tram users who are of both genders, male and female and of all age categories. We observe on the histogram that 46.80 % are bothered by the noise and this dissatisfaction rate is very high.

Fig. 13Overall sample analysis

In Fig. 14 we notice that 47.71 % of women and 46.10 % of men are not satisfied of the disturbance caused by the noise inside the tram. Therefore, it is about half of women and men responded to the questionnaire that they are very annoyed by this noise. In order to validate these conclusions, we test separately:

Null hypothesis$H_0$: $p=1/2$ versus $p>1/2$, where $p$ is the probability that a woman is annoyed by the noise. $H_0$ means: there is the as much woman bothered by the noise as woman who are not. The chi-square test statistic is calculated by using the equation:

It follows a Chi-squared distribution with a degree of freedom equal to one. $N_i$ is the observed frequency, and 100/2 is the expected frequency under the null hypothesis.

We will compare the value of the test statistic $D^2$ to the critical value $d_{\alpha }$. We reject the null hypothesis $H_0$ if $D^2>d_{\alpha }$, $d_{\alpha }=$ 3.841$$if $\alpha =$ 0.05$.$After calculation, we get:

We see that 0.2098 < 3.841, so we accept the null hypothesis $H_0$.

The same thing to the variable men since that the sum of the column is equal to 100 %.

Null hypothesis $H_0$: $p=1/2$ versus $p>1/2$, where $p$ is the probability that a man is annoyed by the noise. $H_0$ means: there is the as much man bothered by the noise as man who are not:

We have 0.6084 < 3.841, for that we accept the null hypothesis $H_0$.

Fig. 14Sample analysis of passengers by gender

Fig. 15 shows the sample according to the age of the passengers. The main categories of users who are aged of between 18-36 years old corresponding to the category of young people and who are between 37-55 years old corresponding to the category of workers. We observe that two categories of age are bothered by the noise inside the tram, young and adult people who are aged of between 18-36 years old and 37-55 years old because these categories use always tram.

1) For the first category 18-36.

Null hypothesis $H_0$: there is the as much persons bothered by the noise as persons who are not between 18 and 36 years old.

$D^2=$ 0.1681. We have 0.1681 < 3.841, for that we accept the null hypothesis$H_0$.

2) For the second category 37-55.

Null hypothesis $H_0$: there is the as much persons bothered by the noise as persons who are not between 37 and 55 years old.

$D^2=$ 0.033124. We have 0.033124 < 3.841, for that we accept the null hypothesis $H_0$.

We observe that the category of old people is not bothered by this noise like the other two categories. To validate this, we take:

Null hypothesis $H_0$: there is the as much persons bothered by the noise as persons who are not between 56 and 75 years old.

$D^2=$ 11.115556. We have 11.115556 > 3.841, for that we reject the null hypothesis $H_0$.

There is much persons who are not bothered by the noise than who are in this category.

Fig. 15Sample analysis of passengers by age

8. Conclusions

In this paper, the problem of noise emissions of tramway is tackled. Contrary to previous works, this one is realized inside the tram in order to measure the noise felt by the passengers. The purpose of the current study was to determine if the comfort of passenger is affected by this noise. Moreover, to show if that may influence their choice for means of transport and its impact on the road traffic.

The results of this investigation show that the rail, rolling stock like bogies and the traction system like equipment on the roof, are the main causes of noise inside the tram. It was also shown that the noise in the interior of the tram increases proportionally with its velocity. It is also noticed that a non-optimal exploitation will degrade rapidly the lifetime of railway and also the rolling stock. This issue will cause a bad contact between the wheel-rail and the noise will increase.

This study has found also that the number of passengers and especially their behavior affect the noise levels inside cabins.

The conducted investigation has shown that almost half of users, men and women are disturbed by the noise. It affects negatively the comfort of young and adult people, because these categories use always tramway. This result will increase the level of congestion if the bothered population change the mode of transport. Otherwise, the high sound of passenger’s information bothers passengers and also who works inside the tram. These last have testified that at the end of the day they have a headache due to this noise.

Several recommendations should be taken in order to reduce the noise inside tramways and increase the comfort of passengers. The exploitation timetable of tramway should be optimized taking into account the actual situation of road traffic, the lifespan of the rolling stock and the track. In order to increase this last and decrease congestion in important crossroads, the time between the tramways must be augmented. Rolling stock does not wear out quickly and the railway not rapidly degraded by the high traffic of the trams. The optimal management of the trams allows to better assign the passengers to the cabins and helps passengers to keep calm. This may avoid the increase of noise in the tram.

An effective maintenance should be applied to the rolling stock, the rail and traction equipment to keep them in a good state and to generate a less noise. Some technical recommendation must be applied to reduce the noise due to contact of the wheel and rail, like lubricating the rails and sending sand in the wheels by the driver when the tram passes across sections that make noise.

Using some materials that help to absorb the noise such as rubber plates and green belt along line sections where high noise is measured. It is also necessary to reduce speed in critical sections which contain a high noise level. The sound of the passenger information system should be adjusted around 65 dB (A) to make the tram more comfortable for all users.

This study may be considered as a contribution to future works that aims at making the tramway more comfortable and more efficient. These two last factors make the tramway more attractive which will incite people to use it than other means and that will help to reduce congestion in urban areas.