Dr. V M Tom1
vmtom@iitb.ac.in
Environmental impact analysis (EIA) is developed as a tool to address environmental issues in decision-making. Over the past few decades EIA systems have been adopted worldwide and the EIA process has evolved to meet the concerns about decision-making process to strategic environment assessment. Human beings in their endeavor to better living standards and development often exploit the natural resources. Historically, this started by human settlers burning forest, construction of roads, manipulating river courses for navigational and agricultural purposes etc., and was limited to minor local issues. However, the impacts triggered by the industrial revolution had wide and deeper consequences on human life. This has lead to a reactionary damage control measure during the middle of past century. Fortunately, now the focus is shifted to the prediction and mitigation of impacts.
Sustainable economics is usually seen as consisting of three interconnected components: ecological (or environmental), social (or human), and economic (Petts, 1999). The environmental focuses on preserving the resilience and dynamic ability of biological and physical systems to adapt to change. The economic approach is based on the concept of the maximum flow of income while at least maintaining the stock of assets or capital that yields these benefits. The socio-cultural aspect of sustainability focuses on eliminating poverty and defending the rights of the future generations. Maintaining the stability of social and cultural systems and reducing destructive conflicts are sought.
The EIA components and the process that is relevant to transport systems are presented in the figure1. The various impacts of transportation projects on air quality, society, economy, ecology and travel are dealt and they have been quantified so that alternate plans can be compared for their relative impact on the environment. The individual indices are converted to a combined environmental index by which different transport options are compared. The individual indices can also be compared with the relevant standards and if the impact value exceeds, appropriate mitigation’s measure can be suggested. Each of these components is discussed in detail in the following sections followed by a case study to illustrate the methodology (see Figure 1).
The most important environmental impact due to a transport operation is the air
pollution. The polluting factors include emission of acidifying and green house
gases such as Carbon dioxide (
) and Nitrogen oxides (
); and
ambient air pollution caused by the emission of CO, , suspended
particulate matter etc. Most transport development activity may have some
adverse impact on the air quality for that invariably increases vehicle
mobility and thereby emissions. Hence, there is a need to understand the nature
of air pollution, methods to quantify and measures to mitigate them.
Canter (1996) has identified six generic procedural steps in assessing air quality; identification of the air quality impact of the proposed project, description of the existing air quality, identifying relevant air quality standards, impact prediction, assessment of significant impacts, and identifying appropriate mitigation measures. Accordingly, Air pollution impact assessment procedure is formulated and elaborated below:
The fourth step is to find the future ambient air pollutant concentration due
to the implementation of the transport project. This is done by gathering
information on the general characteristics of the study area in relation to air
dispersion. Different models exist in finding the pollutant dispersion along a
road stretch (Rao, et al, 1980). Air quality model relates air pollutant
emissions to the resulting ambient air pollutant concentrations under different
topographical and environmental settings including meteorological conditions.
The output of the modeling gives the pollutant concentration at specified
locations. The most commonly used basis for modeling pollutant dispersion is
the Gaussian Plume formulation, since they are less complex in nature and
proved to have higher correlation coefficient (Rao, et al., 1980). The
pollutant concentration C at a point specified by y and z coordinates near a
road is given by Watkins (1984)
is the pollutant emission rate, 
is the traffic flow in
vehicles/hour, 
and 
are the standard deviation of plume
concentration distribution in horizontal and vertical directions, 
is the
wind speed and 
is the emission height.
Thus 
is calculated as a sum of contributions from a series of point source
representatives of the road.
The plume concentration standard deviation ( and ) depends
on the atmospheric stability, which is categorized according to the wind speed,
downwind speed and crosswind distances between the source and the receptor.
In the fifth step, the model determines the values of indicators or indices to
reflect air quality impacts of the transportation alternatives on an area using
the estimated pollutant concentrations from the previous step. Since there are
a number of pollutants, a combined index considering all of them need to
developed for easy comparisons. Thus air pollution index (API) is devised to
transform diverse data into a single quantity and is defined as:
, 
, 
, and 
are the predicted
concentration of 
, , 
and 
respectively, and
, 
, 
and 
are the respective standards laid
down.
Transport development and operation activities are major sources of noise pollution while the former is limited to construction period; the later affects the environment for a prolonged duration. Noise pollution is two kinds; the noise disturbances due to road/rail vehicles especially in heavy built up area; and vibration due to heavy vehicles and trains. Although the effects of noise pollution primarily of nuisance type, prolonged exposures are harmful to human beings, building and under ground services.
Noise pollution assessment studies are helpful in determining the noise generated by the use of transportation systems in the community. Akin to air pollution study, the noise level of a new facility is estimated and compared with competent standards. Typically the study involves the following steps:
Ecological disturbances are not always well recognized and treated comprehensively because the transportation systems and their components are usually planned built, and operated locally and on a project-by-project basis. Considered together over time, the individual disturbances emerge as source of larger ecological perturbations that require innovative approaches to understand and control them. Transportation system will have grave ecological consequences even if they do not emit any pollutants (Committee for a study on Transportation, 2001) as it is operated over a vast infrastructure. The pervasive road/rail network is itself a source of many environmental disturbances. The physical imprint of a road/rail may hinder or alter the biological diversity of a region.
The ultimate aim of any transportation project is to improve the quality of life of the people. The social and economic impacts can be broadly classified under the following four sub-headings. The four effects are interrelated but should be studied separately (Curry & Anderson, 1972):
| Steps in the analysis | Methods |
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The various links of a network are interdependent. The nature of traffic flow in a link affects the flow characteristics in others. Hence, it is necessary to take into consideration, the effect of a project on the entire system (Wolfgang & Werner, 2001). The high investment options will obviously be associated with higher levels of adverse environmental impacts.
TCI is defined as the percentage of link length in the sub region exceeding the V/C value of 0.7 for inter-city and 0.87 for down town areas (0.7 and 0.87 correspond to class C and class D levels of service respectively) are directly obtained from the transport model. This is related to the Levels of Service (LOS), which are indicated in terms of V/C. This index is defined as: TCI = % of link length in the sub region exceeding the V/C value of 0.87, where V/C is the traffic volume to capacity ratio. TCI measures the congestion level in a region, and is to be computed for all the transport options.
This index is important from the viewpoint of representing energy efficiency
and reduction in pollution potential of the transportation alternatives. It is
well established with respect to its optimum speed. Vehicular pollution
generation at speeds other than the optimum speed is also high. The optimum
speed for light and heavy vehicles is 65 to 45 kmph respectively, based on the
fact that road condition in the study area would not allow operating vehicle at
higher speeds, and vehicles should at least be run at lower end of the optimum
speed range. 
is defined by the following expression:
is the passenger car unit of light vehicles for road link i,
is the passenger car unit of heavy vehicles for road link i,
is the average
speed of light vehicles on link i,
is the average speed of heavy vehicles
on link i, 65, 45 is the optimum speed for light and heavy vehicles (km/hr).
The environmental impact assessment study of the city of Mumbai, India is presented here. The study titled Mumbai Urban Transport Project II (MUTP-II, 1996) was conducted to evaluate the impact of six transportation options/alternatives, which consider different degrees of investment on road and rail projects. Each of these options is aimed to increase the transport infrastructure of the region. These six options are shown in Table 1.
A sectoral level EIA strategy in formulated to evaluate the above transport options. The steps involved are summarized below. In the first step, the study area was divided into four sectors namely inland city, western suburbs, eastern suburbs, and rest of MMR (Mumbai Metropolitan region). The classified based on their distinct land use, economic and transportation characteristics. They are classified into these areas since they have similar land use and transport characteristics. In the second step, to assess the impact of the transportation projects the following areas of impact are studied:
For the transport modeling, the study area is divided into 110 zones, identified about 1200 links, and about 500 bus and rail routes covering all the sectors. The model generates separate networks for the private and public transport modes are generated for the model.
Air quality indices are used to determine the baseline air quality of the study area as a whole and of each sector. The comparison of the ambient air pollutant concentration levels resulting from the transport options with respect to ambient air quality standards provides measures of impact. API is used as the parameter for comparison, since API will give a single index taking care of all the major pollutants concentration. The central pollution control board (CPCB) has established ambient air quality standards against which API of each sectors can be compared.
The noise impact is assessed for all the sectors. For instance, for the Island City sector has 143 major road links. Although the transportation alternatives will not alter the number of these road links or the total road length in the sub region, these alternatives are likely to affect traffic noise levels. The transport model estimates the traffic parameters required to be used in the noise prediction model. FHWA model (Equations 1&2) is used to predict noise levels at 30 m distances from the road centerline for each road link in the sector for the base year and horizon year. Traffic noise indicators for day time and night time are calculated to represent noise impacts on population living adjacent to road corridors for all transport options in the sector. The results are tabulated in the third and fourth column of table 8. Similar studies are also conducted for other sectors.
In the Island city sector, while implementing all the options except two are not affecting the ecological systems. In one case there is a need to construct a rail section, but that is not giving any ecological impact. However, the next option involves the construction of a freeway that could affect the marine Eco system as this freeway runs close to the coast. A detailed environmental study is conducted for this option in this sector and is reported in table 8. Similar studies are conducted for all other sectors.
The Island city has high commercial activity; mainly in the form of small shops almost on pavements. Obviously the traffic improvements will reduce congestion and improve the flow. However, during the construction and operation phase may cause many adverse effects like the disruption of traffic during construction, visual obstruction of flow etc. Similar approach is adopted for all other sectors.
Both the rail and road projects are proposed under various alternatives aiming at achieving various traffic objectives. Traffic efficiency index (TEI) and traffic congestion index (TCI) are used for the overall comparison of the different transport options. The typical values are presented in table 8. Similar results are obtained for other sectors.
| Indicator/ | API | TNI | TNI | EI1 | EI2 | SI | TEI | TC |
| Index | (Sr.) | (day) | (night) | |||||
| (1) | (2) | (3) | (4) | (5) | (6) | (7) | (8) | (9) |
| Base year | 312.8 | 61.4 | 91.5 | Nil | 0.56 | 10.8 | ||
| Option 1 | 343.0 | 65.4 | 92.07 | 0 | 0 | 0 | 0.52 | 12.5 |
| 2 | 338.0 | 65.4 | 95.03 | 0 | 0 | 0 | 0.52 | 11.0 |
| 3 | 376.0 | 65.4 | 95.03 | 0 | 0 | 0 | 0.52 | 12.8 |
| 4 | 240.0 | 63.7 | 98.73 | 0 | 0 | 0 | 0.46 | 6.9 |
| 5 | 332.0 | 70.3 | 95.73 | 6 | 0 | 0 | 0.50 | 7.7 |
The purpose of the above environmental analysis is to assist the decision-maker to finalize a transportation strategy for the study area. For this purpose, it is necessary that the impacts of the transportation alternatives be subjected to comparison.
Similarly the environmental index for each sector is determined and tabulated in Table 3. To compare environmental impacts of the transport options, the consolidated environmental impact index is computed for all the options for the horizon year.
From the EI score, it is obvious that option 1 is the preferred alternative. However, these are within a close range; the financial implications obviously became the deciding factor. Option 6 is selected as the preferred option considering both EI and the financial aspects.
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![\begin{displaymath}
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