According to the transportation user needs resulted from the factor analyses and the transport diversity criteria based on sustainability and quality of life, the quantitative indicators representing stakeholder needs are introduced in the following, including externality (environmental impact), safety, accessibility, mobility, reliability, affordability, resource over-utilization, operator profit (economic health) and level of universal design.
(1) Externality
Along with the waste, hydro-resource pollution and the negative habitat impacts during constructing transportation infrastructures, externalities caused by transportation consist of air pollution, noise and vibration in operation periods. Regarding to the quality of life and sustainability, the greenhouse effect causing global warming has come into vogue discussions in recent decades. In fact, how to mitigate the emissions has become more crucial challenges than other negative influences nowadays.
Air pollution, measured in terms of emissions per trip by each mode of transportation, is considered as the substitute for externality. Most costly types of emissions are nitrogen dioxide (NO2) and particulate matter (PM10). In Taiwan, the Pollutant Standard Index (PSI) is utilized for representing atmospheric pollution emissions. The index consists of the criteria pollutants, such as PM10, sulfur dioxide (SO2), NO2, carbon monoxide (CO), and ozone (O3).
For each pollutant, a sub-index is calculated from a segmented linear function that transforms ambient concentrations onto a scale ranging from 0 to 500. The PSI is calculated as the maximum of sub-index. The value of PSI exceeding 100 is considered by USA EPA research to negatively impact human health. The indicator of externality shown in Eqn. 3-1 is summed up the maximum of sub-index, the same calculation but the different duration and unit as PSI.
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×Accidents, such as injure, loss of life and property damage, are potential results of transportation behavior. The accident rate traditionally is calculated in terms of accidents per million vehicle-kilometers or the number of accident fatalities and injuries (casualties) per 10,000 registered vehicles. However, the weightings in fatality accidents (class A1) and injury accidents (class A2) are assumed as equal because of the absence of the global acceptable equivalents for the different accident classifications. Moreover, evaluating annual vehicle-km is difficult owing to limited data availability. This study thus defines accident rate as the number of accident casualties per 10,000 registered vehicles, as shown in Eqn. 3-2, with lower accident rate implying higher safety.
x
The indicators of accessibility are different due to the distinct definitions of accessibility among public transit, private vehicle and pedestrian. Based on the literature review, accessibility can be used to assess the equitable distribution of transport infrastructure and services. In public transit sub-system, the accessibility indicated in Eqn. 3-3 is defined as the ratio of the resident population served by public transit, including mass rapid transit (MRT) and bus, to total population. Public transit serving population is identified as the population residing in the service area in which the public transit service is accessible on foot, i.e. 500 meters from the MRT, bus or feeder bus stations.
Because accessibility is determined as the opportunities of the interactions between spatial patterns, higher accessibility implies more nodes served by public transit and users move from their origins to destinations more easily.
x
On the other hand, road connectivity is employed as the indicator to examine accessibility for private vehicles in this study. Eqn. 3-4 shows the gamma index, one of the measures of road connectivity, which considers the relationship between the numbers of observed and potential links. The gamma is between 0 and 1 where a value of 1 indicates a completely connected network.
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Furthermore, pedestrian accessibility shown in Eqn. 3-5 is determined by average pavement width. Meters provide the average measurement unit. The pedestrian friendliness of the system improves with increasing pavement width.
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The mobility of transport users is investigated for all transport users except MRT users and pedestrians. In fact, the mobility of MRT users is relatively higher and more predictable than that of other transport users. Meanwhile, the mobility of pedestrians is lower and more stable. Mobility performance for private vehicle users is judged based on the travel speed.
Eqn. 3-6 shows the average travel speed calculated by weighting the speed at each link by the
length of links. The unit of measurement used is kilometers per hour. Average travel speed is in direct proportion to mobility.
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The mobility for bus users is measured using the ratio of the travel time from zone x to zone
z by private vehicles to the travel time by bus. The indicator of level of bus service is
based on the network performance developed by Blunden and Black (1984) and indicated in Eqn. 3-7. Bus user travel time is calculated from the summation of actual bus travel time (in-vehicle time) and average waiting time. Average waiting time is calculated as half of average bus headway, while average bus headway has a frequency of over 60, and the bus reliability. Bus mobility ranges from 0 to 1. A level closer to 1 indicates higher bus mobility;i.e. smaller difference in travel time from zone x to other zones between car users and bus users.
Reliability is defined as the probability of failure-free operation for a specified time and space. In transportation system, reliability refers to facilities durability in engineering aspect while it represents punctuality in management aspect. In fact, the discussion of private vehicle reliability is deficient due to the difficulty for determining the failure. Besides, engineering reliability highly relates to what safety concerns. This study thus focuses on the public transit reliability in management aspect.
Public transit sub-system consists of MRT and bus in this study. However, the train punctuality of MRT is relatively higher stable since exclusive right-of-way reduces the impact
of external force. The bus reliability indicated in Eqn. 3-8 is the probability of the punctuality in which buses does not fail, i.e. the average waiting time for bus users are less than half of bus headway.
Affordability refers to the ability of particular consumer groups to bear the cost for a minimum level of a certain service (Fankhauser and Tepic, 2007). The discussion of the relationship among social diversity represented by household income levels, mobility and expenses with transportation in Brazil revealed that the people with the lowest household monthly income had a very low mobility but spent about 30% of income with transportation (de Vasconcellos, 2005). Affordability thus becomes a key issue of social equity.
Moreover, a common acceptable measurement of affordability is expressed as the share of utility payments in monthly disposable income. Therefore, the indicator for affordability considered in transport diversity is calculated as Eqn. 3-9, in which the total transportation expenditure is the product of average cost per trip and the amount of monthly trips.
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(7) Resource Over-Utilization
Along with externality, indicators that focus on non-renewable resources are a particularly important environmental issue for sustainability. For instance, Canadian sustainable development indicators emphasize the use of non-renewable resources, renewable resources, land and soils, and air and water qualities (Wale, 2000). Tong et al. (2008) argued that the efficiency of non-renewable resources utilization is a critical indicator for assessing sustainable development performance.
Additionally, the most important non-renewable resource in transportation system implies fossil energy. The indicator shown as Eqn. 3-10 expresses the consumption of fossil energy by the product of monthly trips and the average energy consumption per trip for each mode
m, where m includes MRT, bus, passenger car and motorcycle. Oil equivalent provides
the average measurement unit.m
(8) Operator Profit
From operator perspective, health economy implies positive profit assisting enterprise in financial sustainability. Eqn. 3-11 reveals the operator profit represented by the product of monthly trips and the difference between average fare box revenue and average operational cost per trip for MRT and bus.
(9) Level of universal design
Level of universal design emerged from barrier-free design and assistive technology strives to be a broad-spectrum solution to helps everyone rather than separate and stigmatizing solutions for people with disabilities. Level of universal design is a part of activities around daily life. However, level of universal design is not adopted towards any great extent in transportation industries, particularly in public transit. The measurement of level of universal design is thus determined as the ratio of barrier-free facilities to crucial equipment (Eqn. 3-12), such as the entrances to terminals, platforms and vehicles, circulation and so on.
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