Transport diversity is defined based on numerous concepts including sustainable transportation, quality of life regarding to transport behaviors and the diversity considering difference as well as equity simultaneously. However, no attempt is made to provide a complete coverage of all components. Instead, the aim is to introduce the representative elements and organize them to construct the conceptual framework.
2.3.1 Characteristics of Diversity
Ecologists believe that ecosystems are influenced by various levels of diversity. From the perspective of system analysis, the diversity of components in ecosystem has been useful in constructing feedback loops among elements (May, 1976). Links among feedback loops have enabled nutrient cycles and information feedbacks as well as provided a basis for ecosystem self-regulation (Odum, 1983). Ecosystem resilience has resulted from system diversity, as well as energy and information flow speed (Ferguson, 1996). Furthermore, Rammel and van den Bergh (2003) suggested that higher diversity may contribute to ecosystem stability.
Diversity thus critically influences ecosystems. Additionally, several studies have attached importance to the relationship between diversity and stability in socioeconomic systems.
Malizia and Ke (1993) identified diversity and competitiveness as important influences on unemployment and stability. Furthermore, Templet (1999) examined the relationship between diversity and economic development via empirical studies of energy consumption. Templet proposed that sustainability is enhanced by strategies that promote diversity and resource use efficiency in economic systems. Moreover, de Vasconcellos (2005) proposed that transportation policies should consider the social diversity expressed by income level to meet the demand of non-automobile users.
Diversity has been considered in analyses of the heterogeneity of community structure.
Indicators used to measure biodiversity are based on two essential factors, namely species richness and evenness (Hamilton, 2005). Richness refers to the species number, while evenness denotes the relative abundance of the different species. The most common index used to assess diversity is the Shannon-Weaver Index, also known as Entropy, shown as Eqn.
2-1 and Eqn. 2-2 (Odum, 1993).
∑
×−
=
i
i
i
P
P
H
ln (2-1)=
∑
i i i
i n
P n (2-2)
where
n denotes the number of individuals belonging to species
ii , P represents the
i proportion of the population of speciesi to the total population, and H is the value of
diversity. The diversity index has a value exceeding 0. Evenness, shown as Table 2-2, refers to that the distribution becomes more uniform with increasing diversity while system A and system B include equal number of species.TABLE 2-2 An example describing the relationship between diversity and evenness
Proportion of species
Systems Diversity value Species 1 Species 2 Species 3 Species 4
System A 0.940 0.7 0.1 0.1 0.1
System B 1.386 0.25 0.25 0.25 0.25
In contrast, higher diversity indicates a larger number of species under the same distribution of each species population. For example, the system A with a richer species has a higher diversity while both systems have a uniform distribution in Table 2-3.
TABLE 2-3 An example describing the relationship between diversity and richness
Proportion of species
Systems Diversity value Species 1 Species 2 Species 3 Species 4 Species 5
System A 1.609 0.2 0.2 0.2 0.2 0.2
System B 1.386 0.25 0.25 0.25 0.25 --
In fact, Reeves (2005) believed that diversity without equity could only address difference. From the perspective of transport diversity, richness indicates that stakeholder needs are considered more comprehensively. Conversely, evenness denotes a condition in which needs are satisfied more equitably. Therefore, greater diversity indicates that as the distribution between compartments becomes more equitable, the gradients between compartments reduce, and larger numbers of compartments come to be involved in the system (Muller, 1998)
2.3.2 Definition and Measurement of Transport Diversity
Diverse transport stakeholders have different needs for urban transport infrastructure and services. The main issue in transport diversity thus becomes how to more equitably satisfy diverse stakeholder needs. Transport diversity is defined as different levels of satisfaction within stakeholder needs, expressed as appropriate indicators and measured using the variations in achievement among indicators. Additionally, minimizing the indicator gaps, the remainder of the needs achievement, between the expected goals and present values (as
shown in Eqn. 2-3) is a key objective in urban transportation planning. The normalized value prevents indicator gaps resulting from differences in unit scale.
threshold y goal y
y goal y
y
O O
V m O
−
= − (2-3)
where
m denotes the normalized gap of the indicator referring to stakeholder need y ,
ygoal
Oy and Othresholdy represent the expected goal and minimum threshold of need
y ,
respectively, andV is the present value of need y . The value of the normalized gap
y exceeds 0, and the degree of need satisfaction increases as the gap approaches 0. Meanwhile,n denotes the positive remainder of the gap of indicators, namely the achievement indicated
yby Eqn. 2-4, which is plugged into Eqn. 2-2. Moreover, transport diversity represents the equal satisfaction of stakeholder needs in the form of the Shannon-Weaver Index, presented in the form of Eqn. 2-3. Transport diversity calculated with Eqn. 2-3 comprises two components:
richness, measured by the number of stakeholder groups, which determines the number of terms in the summation, and equability, measured by the evenness of needs distribution across groups.
) 1 , 0
( y
y
Max m
n
= − (2-4)2.3.3 Measurement with Goal and Threshold Value
Based on Muller (1998), higher transport diversity implies that needs are satisfied more equitably when they are considered more comprehensively. Different transport stakeholders, such as users of different modes, operators, engineers, planners and regulators, have diverse needs in relation to transportation infrastructure and services (Eckton, 2003; Koontz, 2003;
Sohail et al., 2006; Soltani and Allan, 2006). Additionally, the needs of vulnerable groups, including low-income, disabled, elderly and remote users, should not be neglected (de Vasconcellos, 2005; Loo and Chow, 2006). Urban transportation system quality should be acceptable to all individuals, and moreover should consider their specific needs and abilities.
Higher transport diversity may be caused by planners taking more stakeholder needs into consideration. However, transport diversity is not increased by policy-makers considering the involvement of more stakeholder needs but ignoring the need to provide for different needs equitably. For instance, given four needs with achievements of 0.2, where system diversity is 1.39, if a new need with achievement of 0.9 is added to the system, then system diversity will
reduce to 1.34. Therefore, more comprehensive consideration of stakeholder needs within an urban transportation system cannot ensure higher diversity. The equity of the level of needs satisfaction thus should be regarded as the essential factor for transport diversity.
Biodiversity depends on both richness and evenness. In this context evenness describes the equality between the populations of every species in Eqn. 2-2. However, formal equality does not represent the substantive equity from the perspective of social science. For example, the equality between mode-shares, including mass transit, private vehicle, taxi and bicycle, denotes that each mode shares 25% of the trips in a transportation system. This sharing would increase diversity but would not be a sustainable target in urban development. To make the equity of needs satisfaction meaningful, setting targets and thresholds is crucial to diversity analysis. Planners could set targets and thresholds for each mode. For instance, the mode-share target and minimum level of transit might be set at 60% and 30%, respectively.
The achievement of transit would be 0 while the present value (25%) would be lower than the threshold (30%), which would reduce diversity. Loo and Chow (2006) demonstrated that the threshold value for sustainability varies with the perceptions of stakeholders, which differ across time and space. Moreover, goals reflecting the expectations of management as well as stakeholder needs must be accepted at the commencement of the process (Barlas and Yasarcan, 2006). Additionally, Steg and Gifford (2005) proposed that governments should set target and monitor transport system progress towards sustainability. Consequently, goal and threshold values should be set via collaborative planning, specifically through consensus building, based on stakeholder and public opinions, along with feedback from experts.
2.3.4 The Priority of Needs
No consensus norm exists for the best method of achieving the stakeholder needs equitably in transport diversity to suit all conditions because the diverse cities provide distinct development backgrounds. In fact, critical priorities, standards, and constraints differ among groups, time and space (Steg and Gifford, 2005; Jeon et al., 2006). Issues related to weighting method thus become important Ordinary weighting methods weigh the criteria according to the importance through preference survey. For example, the proportion of needs achievement including
w , the weight of indicator i, with Simple Additive Weight (SAW) can be
i calculated by Eqn. 2-5.=
∑
i i i
i i
i wn
n
P w (2-5)
However, Eqn. 2-5 appears not to represent the different importance of needs but rather of needs achievement, leading to loss of a convincing planning rationale. Accordingly, the traditional weighting method does not be applied to the importance of needs in this study.
This study thus suggests that the importance of needs should be implied by the goal and threshold value settings. Studies of service quality reveal that expected satisfaction can substitute for the priority of importance (Chen and Chang, 2005; Deng, 2007) while needs are one-dimensional quality elements (Kano et al., 1984). The more important needs require higher threshold values to promote sustainable quality of life. This study thus sets the weight of stakeholder needs regarding transport diversity by setting the goal and threshold values via consensus building meeting in which stakeholder needs are surveyed via questionnaires, the sustainable targets, and the basic level of quality of life. The needs which are the furthest from the target, especially those not reaching threshold, should be given the highest priority.