1. Introduction
As one of the fastest growing sources of global emissions, transportation—and most notably that of individuals—has become one of the principal challenges in the struggle for a sustainability-focused transition [
1]. Daily commutes between the place of residence and the place of work is critical in this endeavour, which has made it the object of intense scrutiny since the 1990s. On the one hand, the literature on the sustainability of commuting behaviours has focused on the place of residence (place of origin) as a point of departure. Past studies have investigated how the built environment of residential neighbourhoods (density, mix of functions, public transport services, etc.) or the socioeconomic characteristics of commuters (income, family status, age, etc.) [
2,
3,
4,
5,
6] impact commuting behaviours. While such studies aim at providing insights on the role of planning policies in fostering urban sustainability, they have been criticized for raising issues of residential self-selection [
7,
8,
9,
10], complicating the generalization of these results. On the other hand, other studies have taken destinations or the place of employment (employment centres) as the starting point of the analysis. Past research has shown how commuting is structured by both centralized (e.g., central business districts or CBD) and diffuse work destinations (e.g.,
edge cities). The trend described in both the US and Canada between the 1990s and early 2000s is that of a relative decline of downtown areas in daily commutes and the rise of suburban and diffuse work locations as new work destinations. However, new important changes have occurred that have not been the object of recent investigations, at least in Canada. The rise of transit oriented development (TOD) areas, the development of peripheral transport infrastructure, as well as new travel behaviour (e.g., commute by bicycle or active mobility options) have emerged over the past decade, complexifying both the structures of metropolitan employment and commuting dynamics.
While a number of studies exist on commuting dynamics in employment centres in Canadian metropolitan areas, most of the previous works have been limited in the number of modes of transport studied, while empirical analyses rely on rather dated or aggregated data which do not adequately allow the identification of emerging spatial structures, polynuclear or scatteration in particular [
3,
11,
12,
13,
14,
15]. Furthermore, aside from France [
16] and other parts of Europe [
17], there is a lack of comparative studies that could shed light on the types of employment centres that emerge as promoting sustainable travel behaviours in the long run across cities. To our knowledge, no study has systematically identified the types of employment centres of Canadian metropolitan areas, while comparing commuting dynamics across Canadian cities over a recent and long enough period to analyze those emerging dynamics. With the aim of filling these knowledge gaps, this study contributes to the literature on urban mobility and sustainability by examining and comparing commuting trends within the subcentres of six major Canadian cities between 1996 and 2016. The study develops a general typology of employment centres as its analytical framework to capture recent polycentric dynamics and the evolution of commuting modes of transportation and travel distances in Canadian metropolitan areas. This framework is empirically applied using Census microdata, which provides fine grained and detailed information on the place of work, place of residence, and travel modes of workers over the period studied. While the results presented in this study provide further evidence of ongoing trends previously described in the literature, they also offer a valuable assessment of the impact of recent developments within metropolitan areas while revealing new trends that have been the subject of a limited number of previous studies. Before presenting the results, the following sections first propose a review of past and recent studies on subcentres and commuting dynamics. The paper then describes the analytical framework developed, followed by the data and methods used. Results, discussions, and a general conclusion follow.
2. Literature Review
Since the Second World War, the spatial structure of employment in major North American cities has shifted from predominantly monocentric compositions, with single city centres, to new polycentric arrangements involving a growing number of subcentres in the metropolitan periphery. Scholars recognize three to four waves of suburbanization [
18,
19,
20,
21]. The first wave, which started as early as 1945, involved the massive decentralization of residential developments and households. From the 1960s, a second wave saw shopping centres and industrial parks emerge on the outskirts of metropolitan areas. A third wave occurred in the following decade, in which a growing number of back-office jobs decentralized toward the metropolitan periphery. A last wave took place during the 1980s, during which jobs in the upper tertiary sector (front offices) started to concentrate in newly established suburban towns. This led to new conceptualizations of metropolitan employment structures—scholars describing the rise of “suburban downtowns,” [
18], “magnet areas” [
22] or “edge cities” [
20]. However, polycentric urban growth is not uniquely North American. Numerous studies have observed that African [
23], European [
24,
25], Asian [
26] and South American [
27] cities are becoming more and more polycentric. In Canada, it has been shown that cities are becoming more polycentric [
28], but to a lesser extent than in the United States, where urban sprawl and dependence on cars is more evident [
29,
30]. Large Canadian cities also differ by their CBD, which remains strong in attracting employment [
31,
32] while facing less competition from suburban municipalities [
33]. However, we can see that commuting dynamics are currently facing major disruptions in major Canadian cities.
This general decentralization of employment in metropolitan areas has had important impacts on commuting dynamics, with an increasing dislocation of traditional commuting flows toward the city centre. In addition to being major generators of daily travel, employment subcentres are usually located near major highways [
34] and are often not easily accessible by public transport. Consequently, personal vehicles are often the favoured mode of transport for commuting toward these areas. Case studies in Montreal [
11,
13,
35], Toronto [
4], New York [
36], Portland [
37], Atlanta [
38] or in the San Francisco Bay area [
39] are unanimous in affirming that the automobile remains the dominant mode of transport in employment subcentres. This may seem evident to many. On the one hand, public transport networks traditionally converge toward the city centre and, on the other hand, employment subcentres are traditionally located in fewer densified areas that are more accessible by automobile. This inevitably reinforces the unsustainable character of these subcentres.
Nonetheless, several studies have argued that in the long run, polycentric metropolitan areas should induce more sustainable commuting flows, as employment subcentres get closer to the workforce established in the suburbs [
2,
11,
40,
41,
42]. The influx of new jobs in exurban territory has the potential to create a new balance between the number of jobs and the quantity of labour—similar to the ideas of
jobs–housing balance [
43] and
co-location [
44,
45,
46]—and therefore limit travel distances.
Furthermore, suburban areas have also seen some major investments in public transport. Since the mid-1990s, investments have been made, in particular, by setting up neighbourhoods geared toward public transport. Under the name of
transit oriented development (TOD) and resulting from the movement of New Urbanism [
47], these districts aim at a mix of housing, services and jobs, friendliness of the built and pedestrian environment, development of sites that are vacant or to be redeveloped, and preservation of the natural environment [
48].
Yet, in many cases, TOD neighbourhoods located in suburban areas appear to be mono functional residential neighbourhoods with a population that specifically works in the city centre. At least, this is the case for the Montreal metropolitan area and its commuter train network [
49]. If so, TOD districts may offer a sustainable mode of transport that is limited to providing access to the place of origin (the place of residence). Hence, many have argued that monocentric cities induce more sustainable commuting flows in the long run, since city centres are easily accessible by public transport, with compact residential areas and a high density of public and active transport infrastructure [
13,
39,
46,
50,
51,
52]. Many have noted that outside the CBD, downtown or inner-city areas with access to public transport networks, very few train stations, metro stations, or bus terminals are located close to commuting destinations (place of work)—whether it is being in shopping centres, industrial parks, or in
edge city developments. Hence, despite residing close to public transport networks, individuals residing in TOD may be forced to rely on their car if they work in areas poorly served in public transport infrastructure, despite the fact that a large number of TOD residents work in the city centre [
5].
At the same time, employment subcentres do not form a homogeneous block and can vary according to their relative location within metropolitan areas, their relative size, growth or maturity. They can also differ in terms of economic activities [
53,
54], which can cause, among other things, competitiveness or complementarity between subcentres [
55]. In fact, several types of employment subcentres have been described in the literature. In Canada, Shearmur, Coffey, Dubé and Barbonne [
53] proposed an intrametropolitan typology of subcentres for the three largest Canadian cities (Toronto, Montreal and Vancouver) by distinguishing between subcentres according to the number of jobs. In Germany, Krehl and Siedentop [
56] have developed a typology of subcentres according to socioeconomic variables, built environment, and land use for four metropolitan regions. Similarly, McMillen and McDonald [
57] identified six types of subcentres in the Chicago metropolitan area associated in particular with temporality (old satellite cities, new industrial/retail suburbs).
In light of what has been said, is the rise of peripheral employment centres promoting more sustainable mobility of workers to their workplace? What types of subcentres evolve toward more sustainable travel modes and commuting distances? Recent developments within metropolitan areas—whether new planning practices (e.g., TOD), the development of peripheral transport infrastructure, or changing travel behaviour—suggest that polycentricity may lean toward more sustainable commuting flows through co-location and a better job-housing balance. This study aims at empirically confronting this hypothesis with the opposite thesis that subcentres rather generally promote motorized travel modes and longer commuting distances. Besides, it is expected that suburban employment centres that have most recently emerged should promote more sustainable travel dynamics, following better planning practices and recent investments in infrastructure. However, before presenting the empirical analyses, data and methods, the article develops the analytical framework on which our analysis is based.
Analytical Framework
This study builds a typology of employment subcentres to explore the evolution of commuting modes and travel distances in Canadian metropolitan areas between 1996 and 2016. This typology is designed to capture the variety of employment subcentres described in the literature and adapted to the Canadian context. This classification further relies on five key indicators and variables previously used in the literature—distance from the CBD, number of jobs, job density, residential density, and employment growth—as discussed in the methods sections below.
These five variables seem to us sufficient to distinguish the employment clusters in our typology. They faithfully represent the characteristics associated in the literature with urban form, such as employment and residential density [
58], employment growth [
53,
59], number of jobs [
53], and distance from the CBD [
60,
61]. On the other hand, the addition of new variables, such as industry types or occupational classifications, would have altered the number of subcentre types and moved away from the representation of urban form.
The CBD area represents the
central business district of a metropolitan region, which is the area containing the “peak land value intersection” [
62,
63]. CBD areas are not large and cover between 0.48 km
2 (in Toronto) and 4.83 km
2 (in Calgary) of land. The analytical framework and definitions of employment centres used in the results sections are presented in
Figure 1.
The
CBD area (1) represents the
central business district of a metropolitan region, or in other words, the area containing the “peak land value intersection” [
62,
63] and the
downtown area (2) corresponds to the vicinity of the CBD area.
Inner city subcentres (3) correspond to the concentration of jobs in central neighbourhoods with medium to high residential density [
64]. Relatively close to the city centre, the territories associated with the inner city are generally equipped with public transport and have witnessed a demographic and economic resurgence in recent decades. The work of Michael Porter [
65] has also underlined the competitive nature of these areas.
Small subcentres (5) and
Primary subcentres and Airports (4) refer to the hierarchical property between subcentres (in numerical terms) and which has been widely used in the urban form literature in the United States [
66,
67], Europe [
24,
25] and Canada [
28,
68]. Moreover, the geographical location of the international airport is generally correlated with the main employment centres [
69]. Indeed, it has been pointed out that export-oriented firms may be attracted by the proximity of airport infrastructure [
70].
Non-distant subcentres with medium-to-high density (6) and Distant subcentres with low density (7) are primarily based on variables associated with density (residential and jobs) and distance from the CBD.
Finally, in terms of economic (de)growth and temporality,
Boom centres (8) and
Declining subcentres (9) are part of the typology. The first type refers to the work of Sultana and Weber [
59] on the rapid growth of employment areas and may be somewhat similar to Joel Garreau’s [
20] concept of
edge cities in terms of temporality—
edge cities are notably cities that were created after 1960. However, in Canada, there is no
edge city in Montreal [
32] and very few in other large cities of the country [
71]. The second type refers to the shrinking subcentres that can sometimes be found in inner suburbs with an industrialized past before World War II [
57].
The methodology for identifying subcentres and the development of the typology are detailed in the methodological section. These types of subcentres will also be analyzed in the results section.
4. Results
In this section, three sets of results will be shown: employment dynamics of subcentres, patterns of commuting trends, and the evolution of travelling distances. For each city, a distinction will be drawn between the CBD and subcentres.
4.1. Polycentricity of Metropolitan Areas
The first results show the evolution of subcentres in six Canadian CMAs between 1996 and 2016. Associated with urban form, four types of zones are shown in
Figure 2: the CBD (
Figure 2a), the downtown area (
Figure 2b), subcentres (
Figure 2c), and the rest of the area (
Figure 2d).
Figure 2 shows that Calgary’s CBD (CGY) has the largest share of jobs among CMAs, but its relative importance declined over the period to the benefit of subcentres—a trend similar to Vancouver (VAN) where the share of jobs in subcentres increased substantially within the CMA.
While in absolute numbers, Calgary’s CBD jobs increased from 86,760 to 113,390 between 1996 and 2006, these stagnated up to 113,620 jobs until 2016. This is possibly due to the oil sands’ shock in 2015—many headquarters in the oil sector clustering in Calgary’s CBD. In the case of the smallest CMAs, the relative importance of subcentres in Quebec City (QC) and Winnipeg (WPG) increased, but to a lesser proportion. In the case of Toronto (TOR) and Montreal (MTL), employment shares of subcentres increased slightly. In sum, the size of these Canadian CMA subcentres increased at different levels. Finally, the percentage of the rest-of-the-area jobs is declining in every CMA, meaning that jobs in general are clustering. However, the gap is wide between CMAs: in Montreal, 62.6% of jobs are not within its CBD, downtown or subcentres, whereas this proportion is only 25.2% in Calgary.
In brief, these four figures show that, in relative terms, employment in Canada’s largest cities has concentrated in subcentres since 1996, which reflects the increasingly polycentric nature of these metropolitan areas. One exception is the Toronto CMA, where the share of jobs in the inner city increased, followed by a slight decline in employment in the subcentres.
4.2. Evolution of Employment by Subcentres
Table 3 shows that the number of subcentres (1% or ≥10,000) and small subcentres (0.5% or ≥5000) increased in all CMAs, except for Toronto where one subcentre and one small subcentre disappeared, although the total number of jobs kept increasing in the remaining subcentres (159,980 new jobs in subcentres and 20,820 in small subcentres). Numerous subcentres appeared in Calgary and Vancouver, and a lot of new small subcentres emerged in the Montreal CMA.
The following figures offer a geographic perspective on where employment growth and new subcentres emerged within the six CMAs.
Figure 3 shows that in the Toronto CMA, employment growth was highest in the north western area, especially in the Brampton East boomburb, in Vaughan, and in the Mississauga-Airport sector. In itself, this last subcentre attracted 154,480 jobs in 1996, and 241,410 in 2016, representing double the CBD’s jobs and making it the biggest subcentre in Canada. To put things into perspective, Mississauga-Airport has more jobs than the Montreal downtown, including its CBD. However, the proportion of jobs decreased in the eastern zone while in contrast,
Harbourfront downtown district employment doubled. For Montreal,
Figure 4 shows an increase in the number of small subcentres between 1996 and 2016, mainly on the north shore of the CMA along Autoroute 640. In the downtown area, jobs in the “Quartier de l’Innovation” (which is part of Griffintown) increased from 10,205 in 1996 to 23,485 jobs in 2016, fuelled by the emergence of a large number of start-ups in this area. Yet, the CBD remains the biggest jobs centre in the Montreal CMA (with 137,685 in 2016), followed by Saint-Laurent (with 73,310 jobs in 2016). In the Vancouver CMA, jobs grew in the eastern part of the CMA, in suburbs such as Surrey and Langley (
Figure 5) and decreased in the East Downtown (−1475 jobs). The CBD is also the biggest centre (111,125 jobs in 2016), followed by Burnaby Centre with 38,270 jobs.
For a medium-to-large-sized city such as Calgary (
Figure 6), jobs increased in all subcentres. While it was almost an agricultural field in 1996, the northern municipality of Airdrie became a subcentre in 2016, gathering 12,105 jobs. New small subcentres emerged along the southern part of the Macleod Trail. The Calgary CBD is still the most attractive centre, but subcentres such as Northeast-Airport and Shepard Industrial grew tremendously. In the case of Quebec City (
Figure 7), growth was less swift than the two previous CMAs: a few changes have been observed, namely Lévis and Saint-Augustin. Unlike the other CMAs, with 15,625 jobs in 2016, Quebec City’s CBD is the fourth-biggest centre of the metropolitan region, following Zone industrielle 440-73-740 (29,930 jobs in 2016), Vanier-Lebourgneuf (24,975), and Sainte-Foy-les-Ponts (20,655). Unlike other CMAs, Quebec City’s CBD can hardly be described as a “real” central business district. The area is defined by the vicinity of the provincial parliament and by the concentration of a few tall buildings, mostly hotels and government buildings, with an absence of financial or business corporations, which mainly concentrate in the Montreal CBD.
Figure 8 shows that job development in Winnipeg mainly took place in the south west part of the CMA, especially in the Winnipeg South-West subcentre, where jobs nearly doubled from 8920 in 1996 to 17,365 jobs twenty years later. Its CBD remains the biggest centre of the CMA.
In sum, for all six CMAs, steady job growth between 1996 and 2016 shows that subcentres strengthened their attractiveness and relative position within each of the CMAs. As such, they also inevitably changed the dynamics of journey-to-work as destination points, to which we now turn.
4.3. Commuting Trends in CMAs Employment Zones
Table 4 shows the results of commuting proportions (car, public transit, cycling, and walking) for three different zones (CBD, downtown area, and subcentres) of the six CMAs.
Between 1996 and 2016, car use dropped dramatically in CBD and downtown areas of every CMA, except for Winnipeg where car use remained stable. In subcentres, the proportion of car use increased in Toronto, Montreal, Quebec City, and especially Winnipeg. In Calgary subcentres, car use dropped between 1996 and 2006 and increased over the next ten years. For Vancouver, car use levels dropped from 82.7% in 1996 to 77.3% in 2016, namely the lowest percentage of all CMAs.
Results show that there is a direct relationship between the share of car use and transit use. Transit use increased in CBD and downtown areas, especially in Montreal, but peaked in the Toronto CBD and decreased slightly in Winnipeg. In subcentres, transit use modestly declined in Montreal and Winnipeg, came to a standstill in Toronto, increased marginally in Quebec City and Calgary, but increased markedly in Vancouver (from 7.2% to 13.3%, which is the largest share of Canadian CMAs).
Not surprisingly, cycling use and walking are less widespread than car and transit use. Nevertheless, bicycle use is growing among CBD and downtown workers, especially in Vancouver. However, less than 2% of subcentres’ workers use their bicycle to go to work and, since 1996, cycling use stagnated. A lack of cycling infrastructure, large distances to travel, and the proximity of highways in subcentres can be reasons to shun bicycles. Walking increased in CBD and downtown Vancouver and Toronto probably because of a residential densification of these areas. Montreal downtown also densified, but our results do not show a correlation. Walking share declined in Quebec City’s CBD and downtown. In subcentres, walking dropped for all CMAs, except for Vancouver and Montreal. Walking in subcentres is still marginal, with scores hovering between 0.7% and 3.5%.
In brief, CBDs and downtown sectors strengthened their use of sustainable transport modes, while car use remains dominant in subcentres. This is probably due to the lack of transit infrastructure. The case of Vancouver subcentres is interesting insofar as shares of transit use increased. This is not surprising, since two new metro lines have been built since 1996: the Millennium Line in 2002, which passes through the Burnaby subcentre, and the Canada Line in 2009, which was built for the 2010 Winter Olympics and passes through subcentres such as Yaletown, Airport, and Richmond Centre.
Figure 9 shows detailed results by types of subcentres. Looking at the results, what can be seen at first glance is that car use decreased not only in CBD and downtown areas, but also in inner cities—possibly due to the residential densification and gentrification of inner neighbourhoods—and in non-distant subcentres with medium-to-high density where there is the presence of universities (UBC and Simon Fraser University in Vancouver). Farther subcentres continue to attract car commuters, especially in
Boom centres, which is reminiscent of the works of Sultana and Weber [
59].
The pattern of solo commuting appears to be similar for medium-to-high size cities (
Figure 10). Commuting toward CBDs and city centres is increasingly sustainable, but to a lesser extent. Surprisingly, in contrast to the three largest Canadian cities, commuting to inner city subcentres has become motorized.
4.4. Evolution of Travel Distances
4.4.1. Toward the CBDs and Subcentres
This section analyzes the evolution of travel distances for CBDs and subcentres. An initial observation is the heterogeneity of commuting dynamics within and across CBDs. Given their dominant position and attractiveness within the metropolitan realm, these areas offer a particular case. On the one hand, workers living away from and even beyond the limits of the CMAs may daily commute to the CBD. On the other hand, several other workers live in inner-city areas and gentrified neighbourhoods, near to the CBD. Recently, numerous condominium projects were developed inside CBD and downtown areas. According to
Figure 11, between 1996 and 2016, average distances decreased toward the CBDs of Montreal, Vancouver, and Toronto, although this decrease is only significant for Montreal at the 0.1 confidence level (
Table 5). Yet, when compared to other types of subcentres where a significant increase in travel distances is observed, this stagnation stands out as a possible manifestation of the back-to-the-city movement limiting the growth of commuting distances in these areas [
83]. In the cases of Winnipeg and Calgary, average distances significantly increased between 1996 and 2016 by more than two kilometres (
Figure 11;
Table 5), which can be explained by (sub)urban sprawl and, unlike other CMAs, a lack of a back-to-the-city movement.
In contrast to CBDs, subcentres show the longest travel distances. Although this is not the case for the Quebec City CMA, the largest subcentres are on average located further away from the residential location of their workforce than that of the CBD (
Figure 12). Journey-to-work distances also significantly increased in these locations between 1996 and 2016 (
Table 5), with the notable exception of Burnaby Central (Vancouver). In this case, residential densification appears to be a possible factor of the significant decline in average distances observed. For other subcentres, longer commuting distances can possibly be explained by the fact that many are located in outlying industrial districts (St-Bonif-Transcona, 440-73-740) or near an airport (North-East-Airport and Mississauga-Airport), where urban density is low and where long distances need to be travelled. Yet, this increase is not significant in all cases (
Table 5), with Montreal’s St-Laurent subcentre distance remaining stable over the period.
Looking at distances of subcentres in each CMA, which include the largest subcentres but exclude
CBDs,
Downtown areas, and
Inner city subcentres, we observe that distances travelled to Montreal and Vancouver subcentres are still larger than distances travelled to their CBDs (
Figure 13). Compared with CBDs, more than two kilometres must be travelled to reach those subcentres, while no CMA has longer commuting distances than CBDs. Note, however, that for all CMAs, distances to subcentres increased between 1996 and 2016 (the case of the CMA is not statistically significant).
4.4.2. Distance Travelled by Types of Subcentres
Figure 14 shows the average distances travelled by subcentre types. We see that the longest commuting distances are found in peripheral subcentres, particularly in
Boom centres (“Boom” in the figure) and
Primary subcentres and Airports (“Primary”). Despite a significant decrease over the period (
Table 6), commuting distances to
Distant subcentres with low density (“Distant”) remain high, while this significant decrease is only found in Vancouver (
Table 7). Finally, it should be noted that the overall increase in commuting distances between 1996 and 2016 for CBDs is explained by the significant increase in distances in the Calgary and Winnipeg CMAs. In fact, in the other CMAs, commuting distances stagnated or decreased (
Figure 11;
Table 5).
5. Discussion and Conclusions
In this study, we investigated the extent to which the recent phase of the rise of peripheral employment promoted more sustainable travel behaviour. We also analyzed the types of subcentres recently evolving toward more sustainable travel modes and commuting distances. Our point of departure was that recent developments within metropolitan areas—new planning practices (e.g., TOD), the development of peripheral transport infrastructure, or changing travel behaviour—tend to provide a rationale for the hypothesis that polycentricity may lean toward more sustainable commuting flows through co-location and a better job-housing balance. By the same token, we expected to find sustainable travel dynamics within emerging subcentres because of better planning practices. We confronted this hypothesis with the opposite view that subcentres rather generally promote motorized travel modes and longer commuting distances. Empirically, our analysis relied on a general typology of employment centres, using Census microdata on fine spatial scale over the 1996–2016 period to observe commuting modes and distances by subcentre types.
In answer to our general question, we found that despite recent developments in planning practices, transport infrastructure and changing travel behaviour, the argument that justifies the physical proximity of subcentres and residential places [
2,
11,
40,
41,
42] (except for the
distant subcentres with low density) does not seem to hold true, at least for Canadian cities. On the contrary, the rise of subcentres does not promote more sustainable mobility of workers to their workplace and seems to attract a workforce that resides in rather remote neighbourhoods and cities. This suggests that a growing proportion of individuals living in municipalities and villages outside the metropolitan region (exurban areas) [
84] work in these subcentres.
Our results have shown that it is in the CBD that commuting distances have stagnated or decreased in Toronto, Quebec City, Montreal, and Vancouver. Population growth in central neighbourhoods and the rise of condominiums in the downtown areas of Toronto, Montreal and Vancouver [
83,
85] seem to play a positive role in limiting the growth of commuting distances. Instead of moving to a larger house in the suburbs, these workers choose to reside close to their place of employment. There is indeed growing evidence that bicycle trips by residents of gentrified neighbourhoods have increased significantly over the past decade [
86]. Similarly, our study reveals that it is no longer the CBD that encourages the longest distances—as is often mentioned in the literature [
11,
14]—but rather in the largest subcentres and
Boom centres (
Figure 12 and
Figure 14). This reveals important new trends that have been the subject of a limited number of previous studies.
Results also confirmed the significant gap between subcentres and downtown areas. Indeed, while the number of cars heading for city centres has drastically decreased (in relative and absolute terms), subcentres have continued to attract large numbers of motorists, particularly in
Boom centres (
Figure 9 and
Figure 10). This may be explained by a lack of public transport infrastructure in these areas. In fact, Vancouver is the only CMA that has seen an increase in the share of transit in its subcentres. It is also the only CMA to have implemented heavy transit infrastructure between 1996 and 2016, which provides important insights for future urban development policies and research.
Finally, this study reminds us that Canadian cities are becoming increasingly polycentric. Indeed, despite the fact that CBDs and downtown cores of major Canadian cities remain strong, with the number of jobs continuing to increase in absolute terms, but decreasing in relative terms, job growth is particularly noticeable in the subcentres, especially in the Calgary and Vancouver metropolitan areas. It is interesting to note that the strengthening of polycentrism can occur at the same time as an expansion in sustainable travel behaviour: the example of the Vancouver CMA shows that the city is increasingly polycentric, but that its subcentres are becoming more sustainable in terms of travel distances and modes. Polycentric city planning can be undertaken in conjunction with the development of public transport. For example, in Amsterdam, the national
ABC policy of the 1990s aimed to plan the establishment of employment centres essentially accessible by public transport and was ultimately “
[…] intended to promote the installation of ‘good [economic activity] at a good place’ […]” [
87]. However, the
ABC policy ultimately failed to reach its goal, since most of the new jobs were located outside employment centres, in areas mainly accessible by automobile [
88]. Could free access to the car ultimately be the key to the prosperity of a job centre? This study has shown that large cities and their suburbs must jointly consider the importance of planning the city on a metropolitan scale and of integrating sustainable transport into it.
For future studies, it is worth noting that this study is part of a pre-COVID-19 context and that the share of teleworking was rather minimal in large Canadian cities [
89]. Whether the impact of the pandemic will have long-term repercussions on employment centres remains an open question. This study has some other limitations, which may open future research avenues. To best correspond to the notion of commuting between home and work, this study relied on the commuting of full-time workers to the place of employment. It therefore does not consider trips associated with shopping or studying, or even trips made by part-time workers. One should remember that daily displacements are not mathematically linear. Indeed, triangular movements, between the place of employment, other places (e.g., daycare, school, grocery store, store, etc.), and the place of residence are often carried out in many households [
90]. Although these trips are more difficult to measure at the metropolitan level, at least from census data, they represent an important aspect of mobility behaviour, which could benefit future studies. In conclusion, our results suggest that public transit infrastructure investments may play a significant role in making subcentres more sustainable, as is the case in Vancouver. Future research could evaluate the degree to which this improvement results from the infrastructure itself or from simultaneous factors, such as the arrival of a class of workers (young, educated and childless) who are generally less inclined to use the automobile for commuting.