The global number of older persons is increasing rapidly compared with younger age groups [1]. According to the United Nations [2], the population aged 65 and over was 703 million, and the elderly population is projected to double to 1.5 billion in 2050. The travel needs of the older population may be even greater than those of the younger population since they have more time for non-home activities and need more social services and health care [3]. The travel behaviour of the elderly is different from that of other adults[4], and they may have different schedules than working adults. Adequate transport accessibility for the elderly is crucial for older people and those with whom the elderly interact daily, specifically where others rely upon support such as childcare and voluntary work undertaken by senior citizens [5]. Older people feel independent if transportation is readily available [6]. Older people mostly prefer driving public transport as a mode of mobility [7]. One of the main reasons to avoid public transport is extended travel time, including long waiting time. This may be an extra responsibility for family members, particularly for younger family members. For all these reasons, the study of elderly travel needs to be separated [8] from that of other age groups.
Transport accessibility measures can identify issues on which action is required to improve the overall transport system and infrastructure. Public Transport (PT) access in urban areas is a critical issue for older people. Many researchers have focused on transport accessibility [9–15]. Travel time and distance are the two most popular variables used to measure accessibility. Most proposed accessibility studies are based on distance measures [16–18]. However, travel time is a critical component which directly affects travel behaviour and choice of travel mode. If the total travel time is higher, the access level is more likely to be lower. Although time-based approaches have been considered on several occasions, they have been rarely discussed for older travellers, particularly when considering time components such as elderly walk time, total waiting time and in-vehicle time it is not discussed to develop indices. In addition, access to various destinations, and PT stops (for train, tram and bus) in small geographic areas are not widely discussed for older travellers. The lack of detailed travel data on older peoples’ travel behaviour is a major reason for the limited research on the accessibility to PT of this group.
This paper focuses on filling the gap in time-based PT accessibility studies for older people. In this research, people aged 65 and over are considered elderly/older people [19]. To encourage older people to use PT, adequate access to various destinations and PT stops is necessary. If a destination is reachable by older people utilising PT, there is a greater possibility of them accessing it. The objective is to develop a time-based Elderly Public Transport Accessibility Index (EPTAI) to calculate access levels for older people in terms of travel time. In this study, metropolitan Melbourne datasets of older peoples’ walk times, travel destinations, PT stops, total waiting times, the older population, the road network and information at the level of the smallest statistical area are analysed to develop the EPTAI. The time-based EPTAI includes different trip purposes, including shopping trips (trips to shopping centres), medical trips (travel to healthcare centres), education trips (travel to education centres) and recreation trips (e.g. restaurants, parks, cafes). The developed index is validated using statistical validation methods, including Pearson Chi-square, Likelihood Ratio, Linear-by-Linear association, Cramer's V, Contingency Coefficient, and Phi. In addition, the performance of the developed index is compared with household survey data and the Public Transport Accessibility Level (PTAL) [20–22].
This paper is structured as follows. The following section (Section 2) discusses previous research studies. Section 3 describes the study area and the datasets used for the development of the index. Section 4 describes the steps in the development of the index, including the calculation of the time and population components. Section 5 presents the index calculation. Next, Section 6 presents the results and discussion and discusses older peoples’ PT accessibility levels in metropolitan Melbourne according to the proposed index. Finally, conclusions and directions for future research are summarised in Section 7.
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Literature Review
Transport accessibility studies can be classified into different classes and themes [23], [24], including social and transport, improvement of infrastructure, accessibility indices and mode choice. However, to date no best approach to the measurement of accessibility has been identified [25]. As stated previously, the two main themes of accessibility indices are time-based and distance-based measures.
2.1 Distance-based Accessibility Theories
Utility-based theory
The advantage of this theory is that individual accessibility is calculated based on a traveller’s preferred activity opportunities/destinations, rather than the nearest opportunity/destination. A key disadvantage is that it requires extensive data on individuals’ travel patterns and opinions [25], [26].
Two-point distance accessibility theory
This type of study measures the distance from one location to a given specific location [27–29]. This type of index has several components, including network connectivity, the distance between origin and destination, service quality, older peoples’ activities, land use, service connections, the trip number and parking details.
Land Use and Public Transport Accessibility (LUPTAI) theory
This measure was produced by destination-based accessibility analysis in Geographic Information System (GIS) mapping and applied to datasets obtained from many sources; using information on land use and road/pedestrian and public transport networks. LUPTAI considers many variables. The disadvantage is that all relevant datasets are not always readily available or accurate [30], [31].
Public Transport Accessibility Level (PTAL) theory
This measure is used in United Kingdom transport planning to assess the level of access of geographical areas to PT [20], [21]. It is one of the most popular measures for the analysis of access levels. PTAL is a simple, easily calculated approach that considers the distance from any point to the nearest public transport stop and the service frequency at those stops.
Recently, the South Australian non–metropolitan elderly study introduced an index known as the Service Accessibility Transport Disadvantage Index (SATDI) [18]. This study aimed to develop a spatial index to quantify the degree of service accessibility/transport disadvantage for the older population of two specific regions of South Australia. The first component included accessibility to key services utilised by older people. The second component quantified public transport options. However, STADI focused only on accessibility to public buses for older people and assessed bus frequency and walking distances for the elderly.
2.2 Time-based Accessibility Theories
This research study introduces an index based on time-based approaches. Although the time approach has been applied on several occasions [32] [33], for older people time-based accessibility index is not discussed widely. Many researchers around the world have worked on older travellers’ active transport based on time-based measures [24] [34–41]. Some existing time-based index studies can be summarised as follows.
TTSAT theory
Cheng and Agrawal [42] presented a time-based Transit Service Area Tool (TTSAT), which is mainly a mapping tool. TTSAT considers transit service areas based on user travel time (i.e., walk time, wait time, in-vehicle time, etc.). The elderly population is not considered in this measure.
Person-based measure theory
Kim and Kwan [43] proposed a person-based measure in a given time frame, which is mostly applicable to small sample sizes.
LITA
Wiley et al. [44] used three primary time variables to develop and calculate the Local Index of Transit Availability (LITA). LITA considers the frequency of the public transport service, coverage of service and population.
Detailed research on the improvement of metropolitan Melbourne liveability has been conducted by the Department of Environment, Land, Water and Planning [45]. This study presents a detailed plan for neighbourhoods accessible to different necessary destinations within 20 minutes. However, this study does not discuss the level of older commuters’ access to metropolitan Melbourne. According to the Senior Final Report [46], the mean walking trip time for older people is 13.7 minutes, compared with 12.5 minutes for younger adults. For each destination, two thresholds, the desirable and maximum walking travel times, differ for the elderly from those of other adult groups. These values were adopted and converted from Austroads, the Association of Australian and New Zealand Road Transport and Traffic Authorities ([47].
A common similarity among existing time-based studies is that none discuss the access of older travellers to PT and walking travel separately for different destinations accessed by older people. For each destination, the travel time of older people differs depending on the walk time to the destination, in-vehicle time and average waiting time. These affect the overall accessibility level for that specific destination. For example, accessibility to healthcare centres and recreation centres differs because of the variation in travel time. Therefore, it is important to calculate each destination’s accessibility level for older people separately to obtain more accurate results. Other issues for these previous studies are generally relate to older peoples’ mode choice preferences considering a specific larger case study area. If the PT access level is better for older travellers, preference for PT for day-to-day travel can be increased. Therefore, it is important to identify the access level for future PT access implementation and improvement. This paper also evaluates SA1s as a case study area for the analysis of more microscopic access levels considering older peoples’ travel.