1. Introduction
At the city scale, it is expected that transport demand will double by 2050 within the Organisation for Economic Co-operation and Development area [
1], with a corresponding doubling of car use, unless specific low carbon policy options are successfully implemented. Considering the scenario of maintaining the 2015 levels of private car use in cities, the International Transport Forum [
1] suggests that 70% of emissions reductions could potentially come from new technologies, but that 30% need to come from changes in human travel behaviour. There are important health consequences, especially for children, of encouraging higher shares of active transport mode use [
1,
2,
3].
The extent to which the urban form influences people’s travel patterns has long concerned researchers and policy makers. Efforts to promote the use of sustainable travel modes (walking, cycling, and public transport) have been less effective than expected, with some researchers concluding that many regions can now be classified as ‘car dependent’ [
4,
5]. To reduce car dependency, alternatives to car travel are required. The availability of these alternatives and its effect on the mode-share for non-commuting trips is the subject of this paper. Empirical data from a medium sized European city-region are used to explore the determinants of the mode-share and the level of car dependency in different areas within the region.
Despite a considerable research effort in understanding car dependency, policy responses to reduce it have been limited. While it is clear that higher densities support less car use, it is less clear how to provide for alternatives to car use in areas with very dispersed development patterns. The lack of emphasis on non-commuting trips may have contributed to this, as well as the difficulty of understanding which parts of the urban form influence which elements of travel behaviour [
6]. The research presented here addresses this imbalance by examining the effects of contrasting urban forms (i.e., not all compact development) on travel behaviour. The development of a bespoke means of characterising land use–transport typologies is an approach adapted specifically to non-work trips, which is relatively less well covered in the research literature. A key component is the land use mix, as this affects, in large part, the distances to be travelled for non-work activities. A novel means of formulating the land use context for non-work trips is presented as part of the analysis here.
1.1. State of the Art
Litman describes car dependency as a “self-reinforcing cycle of increased car ownership, reduced travel options and more dispersed car-oriented land use patterns” [
5]. This concept underpins the analysis, presented here, on non-work trips, in that car ownership, travel options and land use patterns are the principal elements. It is well-established that the urban form has an influence on travel behaviour, but by way of analysis and measurements, there are multiple methodological and theoretical stumbling blocks [
6]. In fact, the direction of the relationship and a conclusive result as to which parts of the urban form influence which elements of travel behaviour remain elusive [
7,
8,
9]. Knaap et al. [
9] suggest inter alia that the effects of increasing density will depend, to a significant extent, on the existing density within a specific space or population. This means that efforts to increase density, as a planning response, may not have the intended outcome. Meanwhile, Handy [
8] points to methodological issues in addressing this relationship and claims that much of the available research is framed too narrowly. Moreover, she suggests that additional measures are required to reduce car use, apart from compact development.
Stevens [
10] revisits the question in a recent study, using a meta-analysis and regression analysis to evaluate the literature from the period 1996–2015, and examines whether compact development results in a reduction in vehicle miles travelled (VMT) and, if so, what the magnitude of this effect is. He finds that, while overall, there is a reduction, the effect may be smaller than that generally understood or expected by planning practitioners. His results show that the strongest influence on VMT is the distance to downtown or the city centre, with an elasticity of −0.63. This shows that, if the distance decreases by 1%, a household’s driving goes down by 0.63% on average. He also presents the household or population density, with an elasticity of −0.22, which shows that people drive less in areas with higher densities. However, he also recognises that increasing the density in a city is a very difficult process. He shows that, if a city is successful in increasing the density by 40%, driving trips might decrease by 9%.
To investigate, in detail, the potential for land use–transport system interactions in order to increase the use of sustainable transport modes (walking, cycling and public transport), the analysis described in this paper develops an accessibility measure (composite measure), as well as land use measures, e.g., the residential density (direct measure), proximity and intensity of retail facilities (land use mix measure) and socio-demographic factors.
This expands on the axiom presented by Ewing and Cervero [
7], which states that individual trip generation is primarily influenced by socio-demographic characteristics, and trip distances mainly influenced by land use patterns and socio-demographics constitute a secondary factor. Increasingly, a range of other factors, such as life stage, life style, psycho-social and attitudinal factors have been shown to influence non-work travel behaviour patterns [
10,
11,
12,
13,
14,
15,
16,
17].
1.2. Operationalising the Research
Litman [
18,
19] summarises the wide range of meanings and considerations afforded by the term accessibility with an emphasis on how different practitioners understand it (e.g., transport planners—mobility and traffic; land use planners—distance, time and communications; and connectivity and social service planners—ability of those with additional needs to access services). Meanwhile, Geurs and van Wee [
20,
21] provide a detailed account of both the theoretical underpinnings and the minimum expectations of the term, as applied in the evaluation of integrated transport-land-use planning. They note that the complexity involved in incorporating four distinct elements, comprising land use, transport, temporal and individual components, means that, in practice, researchers and practitioners tend to rely on a particular perspective to suit their needs (see [
20] for a full treatment of this).
As a minimum for transport planning and land use planning, accessibility is defined as the distance to a particular activity (see, e.g., reference, [
22]), while in studies of non-work trip destinations, it is often adapted for specific activities. For example, Fan and Khattak [
23] define four indicators of accessibility, specifically for retail and dining. These include both count and distance measures. Prior to the development of accessibility, as a means of both analysing and evaluating land use–transport strategies in the evolution of approaches to transport planning (see, e.g., reference [
24]), much of the literature relies on the five Ds, despite the known limitations (see, e.g., references [
25,
26]). As Stevens [
10] sets out, the five Ds typically refer to:
Density: Population, households or jobs per unit area
Diversity: Mixture of different land uses, often represented by the land use mix variable, and sometimes the jobs-housing balance
Design: Street network characteristics: the density of intersections and proportion of intersections
Destination accessibility: How easy it is to access trip destination: the distance (often to the city centre)
Distance to transit: Distance from a household to the nearest stop
In the current analysis, a composite accessibility measure is computed, which includes both the proximity to public transport, as well as the level of service variable. Meanwhile, density is included as a residential density factor (dwellings per hectare), and diversity is incorporated by way of the land use mix.
Land use mix factors are discussed in the literature by Boarnet and Sarmiento [
27], who highlight that the variation in approaches to examining non-work travel behaviour patterns is due to the plethora of indicators and conceptualisations used to operationalise research. The land use mix is especially important in relation to non-work trips, as it has a large bearing on distances to reach different types of activities. Gehrke and Clifton [
28] describe the conceptualisation of the land use mix as including three elements: land-use interaction; geographic scale and temporal availability. In considering the land use mix, they propose the classification scheme of Song and Rodriquez [
29] and Brownson et al. [
30], as set out below:
Accessibility (distance based): Not always considered a land use mix measure
Intensity of the activity type: A count or percentage—the number of opportunities related to a land-use type within an area and/or the percentage of land in a defined area dedicated to the activity
Pattern: Spatial pattern identified as the variety of land use types within an area (composition) and their proximity to one another (configuration)
Here, we rely on a composite indicator—accessibility—which includes both spatial and temporal elements. The temporal aspect relates to the frequency of the public transport service (referred to as a level-of-service in the transport planning literature (see, e.g., reference [
18])), rather than the availability of land uses (as suggested by Gehrke and Clifton [
28]). It is a composite measure, as it also includes the distance to the bus stop or rail station. This is important, as accessibility has historically been considered from the perspective of planning for cars, rather than public transport modes and active modes (walking and cycling). Elements of the pattern (as defined above) are encapsulated using another composite measure. The intensity of retail activities, combined with sufficient proximity to residences to provide for active transport is computed (regardless of the availability of public transport infrastructure or walking and cycling infrastructure). This approach follows Rajamani et al. [
31] but diverges from Boarnet and Sarmiento [
32], who use retail and service employment density. While individual measures of each land use variable have been used in other regression analyses, a system of six land use transport typologies (LUTTs) was developed for use in the current study.
1.3. Selecting Indicators for Non-Work Travel
Environmental concerns linked to the share of carbon emissions from the transport sector in contributing to climate change has caused policy efforts to focus substantially on the area of CO
2 emissions reductions [
33,
34]. Vehicle kilometres travelled (VKT) is a key indicator and reducing VKT leads to reductions in emissions. There is a strong health imperative associated with increasing active transport in combatting increasingly sedentary lifestyles [
2,
3], and it appears that there is an untapped potential with respect to non-work journey purposes. In addition, while replacing fuel types for car travel reduces emissions, the health benefits of active transport are not accrued. Therefore, it is important to consider the mode-share and encourage active transport use (and public transport use), as a means of improving health outcomes as well as the condition of the environment [
2,
33].
Non-work trips have both a higher frequency and comprise a higher proportion of trips than commuting trips (e.g., data from England suggest that non-work journeys accounted for over 85% of all trips in 2017 [
35]). In addition, there are socio-demographic segments that are not formally working (commuting), and their travel behaviour and options for sustainable transport use are overlooked in traditional analyses of commuting travel behaviour.
Commuting trips tend to be longer than non-commuting trips (for example, in England, the average distance travelled for commuting trips was 1309 miles per person per year in 2018, whereas for retail, it was 738 miles per person per year [
36]). However, in the under-researched area of non-commuting travel, alternative indicators to total vehicle kilometres, such as trip frequency (trip rate) and mode-share by journey purpose, are also important [
31,
37,
38,
39]. This is, in some part, due to the heterogeneity of the spatial structure for non-work activities. Handy notes that opportunities available to residents must be evaluated in some detail to capture subtle differences in the urban form. Additionally, the quality of an available choice must be evaluated in terms of its availability [
37]. For example, being close to a high-speed railway service, a high-quality service, is irrelevant, if the frequency is low, or it does not stop at the local station. In that case, its availability is poor, or its quality is low. There are also considerable limitations regarding the provision of public transport in low-residential-density areas, which considerably reduces the available options (e.g., reference [
37]).
Chatman [
38] uses non-work travel frequency as a key indicator (dependent variable), while distance measures are included as independent variables. Rajamani et al. [
31] describe non-work travel behaviour using the mode-share per trip type, rather than distance. Handy [
37] relies mostly on the destination choice, variety of destinations, factors influencing the choice, mode choice and trip frequency, rather than the average distance, in her analysis. Boarnet and Sarmiento [
32] rely on the frequency of non-work trips, as the key dependent variable in their analysis.
In the analysis in this paper, typologies of land use transport characteristics are defined using a spatially explicit method. Six categories (land-use-transport types [LUTTs]) are used to compare the travel behaviour of residents in different area types. In this way, the level of possible active transport use is implicit in the categorisation of the LUTT. This is important, given the variations in the spatial pattern of the road and transport network across the region and the differences in accessibility by walking and cycling, compared with car use. Previous studies are usually drawn from areas with grid-like street patterns, where it is normal to use the number of road intersections as a measure of connectivity (see, e.g., references [
27,
40]). However, given the heterogenous road pattern in the study region, this measure has been omitted from the current analysis. In addition, the interpretation of the results is more readily targeted at specific land use transport types and provides for a more robust specification of the policy requirements. The method for defining the typologies is presented in the Materials and Methods section.
1.4. Socio-Demographic Effects
The influence of socio-demographic effects on travel behaviour is well-established. Researchers often rely on car ownership levels, as a key indicator influencing travel behaviour patterns, as undoubtedly households with higher levels of car ownership tend towards higher shares of car use. However, as noted, this type of analysis does not necessarily elucidate whether there are viable alternative options in place (for example, distances to facilities that are suitable for walking and cycling and high-quality public transport). In a case in which there are available alternatives, it can be argued that subjective factors may influence the persistence of high levels of car use. Clearly, if there are no alternatives, it is more challenging to provide viable policy solutions to reduce car use. It is in those areas, where there are alternatives, but car use is still high, that there is opportunity to look at policies to encourage alternative behaviours [
41,
42,
43].
Stead [
14] argues that socio-economic factors have a greater influence on travel patterns than do land use factors. Meanwhile, Buehler [
44] compares the use of active and public transport modes in the USA and Germany. The presence of a car, while facilitating car-based transport, does not necessarily lead to car use, as developed in Buehler’s study [
44]. He compares the levels of car use in the US and Germany and highlights the effects of the availability of alternatives. While both have high levels of car ownership, in Germany, the shares of active and public transport trips are four times higher than those seen in the US. This is because, in Germany, active transport use is supported by the spatial structure and appropriate infrastructure. In contrast, Susilo et al. [
45] found, in a UK study, that even where supports are in place for active transport, both for commuting and non-work trips, there remained a preponderance of car use.
To explore both the influence of land use–transport characteristics and socio-demographic factors on non-work travel behaviour, the study addresses the following key research question by proposing four sub hypotheses. In this way, an understanding of the level of car dependency in different area types can be investigated and expand on the overall research question: What factors influence the mode-share for non-work trips?
Do contrasting LUTT characteristics have a similar effect on different types of non-work trips?
What is the difference in magnitude between the effects of each LUTT on the proportion of trips by a sustainable transport mode (aggregated for all 14 destinations)?
How important are income and car ownership in determining the mode-share for non-work trips?
How is income related to the level of car ownership and volume of non-work trips?
3. Results
In this section the key research question looking at what factors influence the mode-share for non-work trips is addressed through the analysis associated with each of the four sub hypotheses. The results show that, in areas where compact development objectives, with supporting high-frequency public transport, can be met, there is an associated reduction in car use (LUTT1). However, in areas with lower residential densities and differing levels of public transport availability, there are significant challenges to reducing car dependency (LUTT2–LUTT6). More importantly, despite significant differences in public transport frequency between LUTT3 and LUTTs 4–6, the mean level of the proportion of total trips by sustainable transport modes was not of a comparable magnitude. Using both the measure of accessibility and the novel land use interaction measure related to retail intensity provided a new means of characterising the land use–transport characteristic of each area. While this approach was used in response to the research needs in the literature, the findings, presented here, did not diverge significantly from those presented in the existing literature. Thus, the results add to the body of evidence indicating that land use transport interactions must be considered in finding solutions to car dependency. The supply of bespoke communal transport options and more effective ways of managing land use patterns in these areas are essential.
Given that the journey purposes with the highest levels of car use were retail, family and friends, sports centre and swimming pool visits, these activity types should be prioritised in focusing efforts to provide alternatives to car use. The results show that, where distances allow for walking or cycling, respondents can reduce their car use. The location of local medical centres/doctor’s surgeries, pharmacies, post offices and local shops is shown to be effective in supporting active transport use, despite lower residential densities and dispersed settlement patterns. Activity destinations for sports, swimming, visiting friends and family and retail feature higher levels of car use. This is often due to retail clustering at the edge of town developments, chosen primarily for their high accessibility by car, but with active and public transport facilities often overlooked. The highest levels of public transport use were seen for trips to the cinema, theatre, social club and classes. This demonstrates that the clustering of these activity types can support sufficient patronage levels for public transport services. However, it may also be due to the co-location of work places and mixed-use activity centres. The next sections set out, in detail, the results of the analysis, carried out to address the research sub-hypotheses.
1. Do contrasting LUTT characteristics have a similar effect on different types of non-work trips?
As shown in
Table 4, for each of the 14 destinations included in the survey, the proportion of people who use a car to reach them, compared with those who do not, was statistically significant (
p < 0.001). The strength of the association is assessed using Cramér’s V values, which are shown in the column on the far right. The strongest association was for the cinema and INTREO (social welfare office) trips (Cramér’s V > 0.4), followed by the theatre, swimming pool, sporting centre and class (Cramér’s V between 0.39 and 0.338), with the weakest association for the pharmacy, post office (PO), General Practitioner (GP), local shop, supermarket shop, family and friends and worship (Cramér’s V between 0.319–0.21). The results show that whether someone chooses to use a car or other modes of transport is associated with the LUTT characteristics of their place of residence. There is some variation between the destination types and the strength of the influence of the relationship between the land use–transport characteristics and mode-share for each trip type. LUTT1 shows consistently higher shares of non-car use for almost all journey purposes, compared to LUTT4, LUTT5 and LUTT6. Considering each destination type in detail,
Table 5 shows the destinations with the highest shares of each of the three main modes: Active mode, car, and public transport.
2. What is the difference in magnitude between the effects of each LUTT on the proportion of trips by a sustainable transport mode (aggregated for all 14 destinations)?
To investigate the mode-share for non-work journey purposes, an analysis was conducted to compare the effect of each LUTT on the proportion of sustainable transport mode use (active and PT). The results show that the mean proportion of trips by sustainable transport modes was statistically significantly different between each LUTT, Welch’s F (5, 164.2) = 15.5,
p < 0.005 (see
Appendix B). This means that the proportion of trips carried out by sustainable transport modes, compared with all trips by all modes, was statistically significantly associated with the land use–transport typology of the respondent. It was statistically significant in the case of residents of LUTT 1, compared with each of the other LUTTs at a high level of significance, and it was statistically significant in the case of residents of LUTT3, compared with LUTT4, LUTT3 with LUTT5 and LUTT3 with LUTT6, at a lower level of significance. The mean for each LUTT is shown in
Table 6, with the standard deviations. A Games-Howell post-hoc analysis revealed that the difference between LUTT1 and LUTT2–6 was statistically significant. In addition, the differences between LUTT3 and LUTT4, LUTT3 and LUTT5, and LUTT3 and LUTT6 were statistically significant, as shown by the confidence intervals and
p values presented in
Table 7.
LUTT1 demonstrates the highest levels of active and public transport use, aggregated for all non-work journey purposes. The levels seen in LUTT1 are almost twice that in any of the other LUTTs. Additionally, the magnitude of the difference in active and public transport shares is small between the other LUTTs and in comparison with LUTT1. This proves that a higher-density mixed use development, with high-quality public transport, supports the use of the sustainable transport mode. Moreover, it shows that the difference between having medium-level transport services, compared with poor transport, and being distant from retail clusters (as in the case of LUTT5 and LUTT6), has a strong negative influence on the level of the use of the sustainable transport mode for non-work journeys.
Table 7 shows the results of each of the LUTTs that were significant. The biggest difference in the mean value of the proportion of total non-work trips was between LUTT1 and LUTT 5, with a decrease of 40.17 (95% CI, 24.1–56.2) between the mean proportion in LUTT1 and LUTT5. The next biggest difference was between LUTT1 and LUTT4, which was 35.9 (95% CI, 22.2–49.6),
p = 0.000, and the next biggest difference was between LUTT1 and LUTT2, at 35.6 (95% CI, 14–57.1), followed by that between LUTT1 and LUTT6, which was 35.2 (95% CI, 21.6–49).
The next three pairs that had significant differences between them, although with a lower significance than the abovementioned ones, were between LUTT3 and LUTT4, at 9.46 (95% CI, 0.6–18.3); LUTT3 and LUTT5, at 13.8 (95% CI, 1.3–26.2); and LUTT3 and LUTT6, at 8.8 (95% CI, 0.1–17.5), with p values of 0.028, 0.020 and 0.048, respectively.
3. How important are income and car ownership in determining the mode-share for non-work trips?
To examine this research question, a multiple regression model was developed, which considered socio-demographic characteristics: income, the presence of children, gender, work status, and both LUTT at residence and car ownership in determining the proportion of active and public transport use by households.
A continuous variable was computed, which represents the proportion of active and public transport mode use, compared with the use of all modes, aggregated for 14 journey destinations and based on the frequency of trips in one year (365 days). The model was shown to be statistically significant, with a likelihood ratio chi-square of 311.123 df 13,
p < 0.001 (
Appendix C). The model showed that LUTT and car ownership are statistically significant, as shown in
Table 8.
Car ownership had the strongest unique contribution to the proportion of active and public transport use for all non-work trips and was statistically significant. The next biggest influence is the land use transport type at residence, which was also statistically significant. The model shows that LUTT1, LUTT3 and LUTT5 are statistically significant, while the other LUTTs are not.
The proportion of the use of the sustainable transport mode was much higher among those with no car, compared with those households with 2 or more cars (B = 55.7),
p < 0.001. For those with one car, there was a higher level of the use of the sustainable transport mode, compared to those with two or more cars (B = 14.856),
p < 0.001. The presence of children, gender work status and income were not statistically significant in this model. This supports the results of many other studies in this field, whereby car ownership is consistently shown to influence the levels of car use. However, the current paper is concerned with the available travel options, and it is therefore important to consider factors beyond car ownership in determining the use of active and public transport use. These include attitudes, social norms and habits. Additionally, research by Buehler [
44] and Boarnet and Sarmiento [
32] shows that car ownership can have differing effects on the mode-share, when alternative options are available.
4. How is income related to the level of car ownership and volume of non-work trips?
To explore more fully the role of car ownership and income, a bivariate analysis was carried out to determine the effects of income on both the proportion of the use of the sustainable transport mode, as one dimension of the non-work travel pattern, and also the frequency (activity level) or total volume of trips, as an alternative dimension of non-work travel. The results are presented in
Table 9. Income and car ownership are positively correlated (N = 959), meaning that, as income increases, so too does the number of cars in the household (Spearmen’s rho = 0.273,
p < 0.001). The low Spearman’s rho value indicates a weak relationship [
62].
To summarise, in the current study, as incomes increase, the number of cars owned by a household also increases, but the relationship is weak in the survey data. To a lesser extent, as income increases, sustainable transport modes are used less frequently, but the relationship is even weaker, although both relationships are statistically significant. There does not appear to be a significant relationship between income levels and the activity frequency.