Numerous definitions and indicators have been studied for their function with sustainability. The purpose of this section is to provide literatures reviews to identify the commonly acceptable definition and practical indicators for sustainable transportation.
2.1.1 Features of Sustainable Transportation
One of the popular definitions of sustainable development is reported by the WCED (1987) as “development which meets present needs without compromising the ability of future generations to achieve their own needs”. The policies of sustainability have to simultaneously consider the external effect in environment, stakeholders’ equity in society, and efficient use of natural resource in economy. Sustainable development is usually evaluated using a set of measurable indicators to track trends of areas and activities and to evaluate the performances of systems. The selected indicators significantly influence the results of analysis. Sustainability is always set in the components depended on the type of system and the spatiotemporal scales rather than an absolute concept (Allen and Hoekstra, 1994). Besides, Maclaren (1996) divided the generators of sustainable indicators into six categories, such as domain-based, goal-based, sector-based, issue-based, causal, and combination generator.
There is much research discussed the different sustainable indicators generators. Some studies related to transportation system are reviewed in this study. Canadian Centre for Sustainable Transportation (CST, 1997) proposed that a sustainable transportation system is based on three principles: First, the basic access needs of individuals and society should be satisfied under a safe, generation-equitable, and ecosystem-friendly condition. Second, the growing economy should be supported under the affordable, efficient, and multi-choice operations. Furthermore, the emissions, waste, noise, and consumption of natural resources
should be limited. Additionally, The Organization for Economic Cooperation and Development (OECD, 2001) suggested sustainable indicators along a causal generator, named
“Driving force–State–Response model,” which is adapted to take into account the specificities of the public sector. The OECD indicators are established according to the tendencies for economic and environmental impact in the various sectors.
Moreover, the World Bank developed the Environmental Performance Monitoring Indicators based on the issue-based generator (Segnestam, 1999). The considered issues included forestry, biodiversity, land quality, air pollution, water pollution, global environmental problems, and institutional capacity. The Institute of Transportation Taiwan (2002) established the sustainable transportation indicators. The indicators had been generated by the method of complete enumeration. In addition, reports of Ontario Round Table argued indicators to evaluate the impacts of development on sustainability. The indicators adopted were based on a “Criterion – Influences – Actions – Measures” system in the combination generator. The concept of transport sustainability consists of three main criteria: acceptable emissions; limitation of resources consumption, and minimizing the disruption of ecological processes, land use, and sensitive habitats (Gilbert and Tanguay, 2000). The reviewed sustainable indicators related to transportation are shown in Table 2-1.
TABLE 2-1 Sustainable transportation indicators
Sources Indicators
OECD Transport intensity, vehicles, fuels consumption, infrastructure, air pollution, safety risks, pricing and taxation, and subsidies.
World Bank Percentage of reliable and affordable linked areas, freight and passenger tariffs, air pollution, and investment of roads.
IOT, Taiwan
Economy: Transit ridership, maintenance cost of roads, passenger transportation by aircraft and railway, growth rate of vehicles, and population density.
Environment: Percentage of preservation areas, air pollution, noise pollution, fuels consumption, number of motorized mode, network density, recycle of disused vehicles.
Society: Transportation intensity, accident rate, subsidies, infrastructures allocation, number of violations, fatal and injury accidents.
Ontario Round Table, Canada
CO2 loading, ecological footprint, habitat disruption, employment, green GDP, tax revenues, commute cost, deaths and injuries, community disruption, distribution inequality index, Demotechnic index, E-index, vehicle access, energy efficiency, mixed land use, and trips with two or more modes.
Different generator with diverse advantages as well as disadvantages fits distinct study purpose. For example, the domain-based generator organizes indicators based on the environmental, social, and economic dimensions of sustainability. Domain-based generator is not used to infer from ex post facto integration of functional resource outputs since it focused on the outcomes and states rather than on inputs and outputs of systems. This generator is the most effective one to ensure coverage of the three dimensions from which sustainability emerges, as well as to examine interactions within and among the three main components of sustainability. Because of the above characteristics, domain-based generator is used in this study.
2.1.2 Practical Sustainable Transportation Indicators
Indicators expressing the needs of stakeholders are established based on the criteria of transportation system performance, including mobility, accessibility, safety, and externality (Wachs and Koenig, 1979; CST, 1997; OECD, 2001; Levinson, 2003). The indicators are briefly described below. Different indicator systems yield the different results. Since this section aims to illustrate how to incorporate transport diversity during transportation planning, it does not focus on which and how many indicators should be included and by which process.
(1) Mobility
Mobility refers to the efficiency with which vehicles operate on roads (American Association of State Highway and Transportation Officials, 1994). As a result, mobility is defined as the capability to overcome spatial resistance. Moreover, mobility refers to the ability of individuals to travel and move (McGillivray and Kirby, 1979; Levinson, 2003), or individual ease of movement (Levine and Garb, 2002).
(2) Safety
Safety is defined as being safe from experiencing or causing hurt, injury, or loss. In fact, the meaning of safe is free from harm or risk. Traffic accidents currently are a major
socio-economic problem. According to Kapp (2003), annual accidents account for 1.26 million fatalities, 50 million injuries, and economic losses of US$518 billion worldwide.
Safety, as represented by accident rate, thus is an important indicator of the social cost of transportation.
(3) Accessibility
Accessibility has been applied to evaluate the network development in transportation planning and to measure the potential of regional economic performance in urban planning (Hansen, 1959). In fact, Martellato et al. (1998) provided that accessibility refers to the potential opportunities of the interactions between the urban spatial patterns. Levine and Garb (2002) measured the accessibility based on the ease of interactions between network nodes.
Besides, accessibility represented the connection between origins and destinations (Ingram, 1971) or that between activities (Wachs and Koenig, 1979). In addition, accessibility indicated the difference in the attraction between activities (Burns, 1979).
(4) Externality
Governments traditionally have constructed extensive transport infrastructure to enhance transport efficiency. Mass emissions caused by motorized vehicles have led to the greenhouse effect and ozone hole, and have also threatened the ecological system upon which human life depends (OECD, 2004). Therefore, the transportation policies of developed countries have changed during recent years to mitigate adverse environmental impacts.