Mobility and accessibility models

There are many studies defining mobility in various ways and developing mathematical models to explore different issues. For example, Meyer (1995) defined mobility as the ability and knowledge to travel from one location to another in a reasonable amount of time for an acceptable cost. Schafer and Victor (2000) used several factors to develop a new technique for projecting future mobility and mode of transport in all eleven world regions from 1990 to 2050. They showed that all world regions illustrated the same phenomenon of shifting from slow to faster modes as income and the demand for mobility rose, and variations among regions largely reflected the historical legacy of infrastructures.

In the case of North America, the high-speed-transport share of mobility would rise fourfold to 71% by 2050, but only 17% of the average person’s travel time budget would be spent

moving at high speeds. It also showed that the average American’s mobility would rise by a factor of 2.6 by 2050, to 58,000 km/year.

Levine and Garb (2002) defined mobility as an ease of movement, and provided a theoretical grounding for current accessibility-based thinking in transportation policy and delineated and distinguished mobility-based from accessibility-based congestion pricing policies. They pointed out that a mobility-based congestion pricing promised to alleviate congestion but threatened to deteriorate from overall regional accessibility as it accelerated metropolitan deconcentration. However, an accessibility-based congestion pricing avoided acceleration of sprawl by incorporating policies to ensure that drivers tolled off roads were replaced with residents and travelers arriving at previously congested areas by other means.

They argued that a mobility-based policy would tend to concentrate benefits at the high end of the income spectrum, while an accessibility-based policy would spread benefits more broadly and equitably. Alsnih and Hensher (2003) took a close look at the evidence on the mobility needs and travel patterns of individuals over 64, distinguishing between the young elderly (aged 65-75 years) and the old elderly (over 75 years). They showed that differences existed between the young elderly travel patterns and needs and the old elderly travel patterns and needs, and that mobility reductions became more evident as people reached 80 years of age. Although women on average live longer than men, older women had a higher disability rate than comparable men and were more likely to require greater assistance in relation to transport activities and mobility.

Cameron et al. (2003) defined mobility as the ratio of the actual total annual private motorized passenger kilometers to the potential total annual private motorised passenger kilometers, and developed a model of urban private motorised mobility based on empirical data from a wide range of cities. They pointed out that as private motorised mobility was

based on vehicle kilometers of travel, which in turn was a surrogate for urban transportation emissions, urban air quality was directly linked to urban structure. Siren and Hakamies-Blomqvist (2004) aimed at describing the present situation in older persons’

mobility options and resources in Finland in order to identify groups of elders with reduced mobility. A mail survey was sent to 2500 Finnish citizens aged 65 and over, and showed that there were a considerable number of older persons experiencing reduced mobility for certain types of trips, mainly leisure-related ones. In addition, older persons were heterogeneous in their mobility options and resources, and demographics were strongly associated with their mobility. After controlling for the interaction and cumulative effects of the background demographic factors, driver license and urban type of residence were the only significant predictors for higher mobility. It implied that the poorer mobility of certain sub-groups was principally due to the lack of driver license and to geographic inequalities in infrastructure and land use.

At the same time, there are some studies investigating accessibility, defining it in different ways and analyzing the impacts of different transportation systems on it. Meyer (1995) defined accessibility as the means by which an individual can accomplish some economic or social activity by having access to that activity. Gutiérrez and Gómez (1999) analyzed the impact of orbital motorways on intra-metropolitan accessibility using the Madrid M-40 orbital motorway as an example. They showed that after establishment, the area around the M-40 had become highly accessible. It also showed that the new orbital motorway had brought about relevant changes in intra-metropolitan accessibility, and the changes in accessibility were greater in the accessibility to population indicators than in those of accessibility to employment. Geurs and van Wee (2004) defined accessibility as the extent to which land-use and transport systems enable individuals to reach activities or destinations by means of a transport mode, and described a set of theoretical criteria related

to the different components of accessibility. These criteria included theoretical basis, interpretability and communicability, and data requirements of the measures. They indicated that location- and utility-based accessibility measures could be considered effective measures of accessibility, which could also be used as input for social and economic evaluations. Person-based accessibility measures were potentially very useful for social evaluations, and may also be tied to the utility-based approach, which opened up the possibility of using them in economic evaluations. They also pointed out that the potential accessibility measures (also called gravity-based measures) were appropriate as social indicators for analyzing the level of access to social and economic opportunities for different socio-economic groups.

Zhu and Liu (2004) investigated the impact of the mass rapid transit (MRT) network on accessibility in Singapore using an integrated GIS tool, and assessed the accessibility to the central business district, to working population, to industrial and commercial opportunities. The analyses showed that the construction of the new North-East line had greatly improved accessibility of the northeastern areas, but had insignificant impact on accessibility of the northern, northwestern and eastern parts of the country. For smaller zones, it should use more accurate estimates of accessibility in the zone, as accessibility could vary greatly across small distances. It also showed that the closer to the central area of Singapore and the East-West MRT line a location was, the higher accessibility it attained.

Dong et al. (2006) defined accessibility as the expected maximum utility over a choice situation faced by an individual, and proposed a new measure of accessibility and compared it to traditional measures of accessibility. They pointed out that activity-based accessibility measure was generated not by examining a particular trip, but by examining all trips and activities throughout the day, while the traditional trip-based measures of accessibility were focused on one trip purpose and did not incorporate scheduling or trip chaining. The

activity-based accessibility measure was shown to be successful in capturing taste heterogeneity across individuals, and in combining different types of trips into a unified measure of accessibility. The kind of accessibility measure improved the ability to quantify the ease and convenience of access to spatially distributed opportunities. Table 2.4 summarizes the main issues and features as well as important results in the existing literature on mobility and accessibility models.

Table 2.4 Main issues, features and results on mobility and accessibility related literature Authors Main issues and features Important results

Gutiérrez and

The changes in accessibility are greater in the accessibility to population indicators than in those of accessibility to employment

Schafer and Victor (2000)

Apply several factors to develop a new technique for projecting future mobility and mode of transport in all eleven world regions from 1990 to 2050

All world regions illustrate the same phenomenon of shifting from slow to faster modes as income and the demand for mobility rise, and variations among regions largely reflect the historical legacy of infrastructures

A mobility-based policy would tend to concentrate benefits at the high end of the income spectrum, while an accessibility-based policy would spread benefits more broadly and equitably Alsnih and Hensher

(2003)

Take a close look at the evidence on the mobility needs and travel patterns of individuals over 64

Although women on average live longer than men, older women have a higher disability rate than comparable men and are more likely to require greater assistance in relation to transport activities and mobility

Cameron et al.

(2003)

Develop a model of urban private motorised mobility based on empirical data from a wide range of cities

As private motorised mobility is based on vehicle kilometers of travel, urban air quality is directly linked to urban structure

Source: this dissertation

Table 2.4 (continued)

Authors Main issues and features Important results Geurs and van Wee

(2004)

Describe a set of theoretical criteria related to the accessibility, which can also be used as input for social and economic evaluations

There are a considerable number of older persons experiencing reduced mobility for leisure-related trips, and older persons are heterogeneous in their mobility options and resources, and demographics are strongly associated

The construction of the new North-East line had greatly improved accessibility of the northeastern areas, but had insignificant impact on accessibility of the northern, northwestern and eastern parts of the country measure is shown to be successful in combining different types of trips into a unified measure of accessibility, and.

improves the ability to quantify the ease and convenience of access to spatially distributed opportunities

Source: this dissertation

Summary:

There is a substantial amount of research carried out on the definitions and formulations of mobility and accessibility, and on investigating the impacts of transportation systems on them. The literature indicated that the potential model is usually used to evaluate the intensity of the interaction between socioeconomic groups at different locations, and is also suitable as a social indicator for measuring the level of access to socioeconomic opportunities. In addition, travel time is the most common and significant component in formulating mobility and accessibility models in the literature. However, there is scant literature available that has investigated the impacts of operations of airlines on the mobility and accessibility of air transportation network. In particular, the issue how international airline alliances influence the mobility and accessibility of air travel for improving the transportation efficiency and connectivity of airline networks has rarely been explored.