The urban area around public transport stops is often considered as a catchment area. Most common is the catchment area understood as a circular area with a specific radius around the stops. The radius represents the distance, at which walking to the stop is considered reasonable. Catchment areas are often considered in a simplified way as a homogenous spatial area around public transport stops.
Together with data on the density of workplaces and residential units, the catchment area provides an estimate of the number of persons that are serviced by public transport. However, urban realities are usually more complex.
Schmitz (1991a, 1991b) differentiates between two parts of the catchment area in which walking differs:
1. The longer section of the walk leading through the footpath network between the public transport stop and the start/destination point of the journey (1991b)
2. The shorter section of the route in the closer stop surroundings (1991a)
The experience of walking in the footpath network varies with the pleasantness of the environmental experience. Conversely, street crossings and interactions with cyclists, buses, and other pedestrians characterise the part of the walking route close to the stop, explains Schmitz (1991b, p. 140). Figure 6 illustrates the differentiation of Schmitz. The definition in Textbox 2 derives from the experience gained
during this current research. Accordingly, Berg (1988) understands the public transport stop as a focal point of mobility, where pedestrians interact with cars, public transport vehicles, cyclists and other pedestrians. The text elaborates the influence of street crossing facilities on time delays and detours along walking routes to public transport stops (pp. 23–28).
Berg (1988) illustrates how the character of the footpath network influences the size of the catchment area. A footpath network with straight, radial footpaths (Figure 7) around the stop appears theoretical and unrealistic. The orthogonal network covers only 64 percent of the area of a radial network, with equal maximum walking distances. A missing orthogonal link at the stop reduces the
Figure 6: Closer stop surroundings and footpath network
The closer stop surroundings represent the area up to a distance of 30 metres around the public transport stop. From here, approaching buses and trams are visible, the stop is quickly accessible, and more shops and services can be available. In the closer stop surroundings, pedestrians have to interact increasingly with vehicles, cyclists, and other pedestrians.
The footpath network comprises all footpaths outside he closer stop surroundings. This network links the surrounding urban area with the closer stop environment. Footpaths can be pavements along the public transport corridor, side streets, pedestrian streets, walking paths through parks, but also informal walking routes.
Appendix 1 presents a more detailed description.
Textbox 2
Definition: 1. Closer stop surroundings 2. Footpath network
catchment area further. Figure 8 shows an orthogonal network with added diagonals that cross at the stop in the centre. The diagonals increase the area to 90 percent of a theoretical catchment area with radial footpaths, as Berg explains (p. 60). The analysis shows how the character of the footpath network and missing links influence the catchment area.
Yang et al. (2012) investigate detour factors in different characterised urban areas around stops in the city of Jinan (China). The detour factor increases to 1.59 around stops at arterial roads. Large super blocks characterise these urban areas. Stops are located at some distance from major traffic junctions. The stop position increases detours as most people approach the stop from adjacent street junctions. Further, the large arterials are impossible to cross informally and so restrict any shortcuts. Streets and city structure are the main factors for detours, according to the authors (p. 8). In urban areas with smaller block size and narrower carriageways, detour factors decreased to 1.33. Section 2.8 presents further details and results from this interesting study.
Lam and J. F. Morrall (1982) found average detour factors in the city of Calgary (Canada) of 1.24.
Figure 7: Variation of the catchment area according to the footpath network (Berg 1988, p. 60)
Figure 8: Optimised orthogonal network with added diagonals (Berg 1988, p. 60)
A walking route between A and B in an urban environment most likely does not equal the shortest, linear distance between A and B. The detour factor is calculated by dividing the nonlinear distance between A and B through the linear distance between A and B.
Textbox 3 Definition:
Detour factor
Around suburban bus stops the factor was 1.25, at stops in central urban areas 1.22, and in industrial areas 1.139. The lower detour factor in industrial areas caused walking routes via parking lots and fields (p. 419). Detour factors exceeded 1.41 for nearly all pedestrians that had to cross a railway line in the central business district. Inversely, detours decrease with longer walking routes to stops (p. 420).
Congruent with Lam and Morrall, Walther (1973) finds rising detour factors with shorter walking distances to stops in Bielefeld (Germany). Average detour factors decrease from 1.33 along routes under 100 metres to 1.11 along routes between 900 and 1000 metres in length (p. 121), as Figure 9 shows. The results of Walther, as well as the findings of Lam and Morrall, indicate that detours increase close to the stop. The footpath network has, surprisingly, a lower influence on detours.
Missing links in the network seem not to be an issue around the investigated stops in Bielefeld and Calgary.
Schmitz (1991b) points out that, when the stop is already in sight, obvious detours and required stops become increasingly unacceptable (p. 140). O'Sulivan and J.
Morrall (1996) consider detour factors up to 1.2 as preferable and over 1.4 as
9 Lam and Morrell differentiated detour factors between summer and winter. The values shown in the text above represent the arithmetic mean for winter and summer.
Figure 9: Detour factor increases with shorter walking distances to stops, X-axis: length of walking trip in metres; Y axis: detour factor (Walther 1973, p. 121)
unacceptable (p. 19). Berg (1988) evaluates detour factors under 1.1 as very good, around 1.25 as good to tolerable, and factors over 1.4 as unreasonable (p. 62).
Whether, and under which conditions, pedestrians experience detours as inconvenient remains unclear. It is likely that the diverse characteristics of walking results in very different experiences of detours.
The catchment area around a public transport stop is often considered simplified, as a homogenous circular urban area, from which the stop is equally accessible. In reality though, the accessibility of the stop depends on the character of the city within the area around a stop. An increasing number of researchers criticise the fact that pedestrian access to public transport stops is often only considered in this simplified manner (Hoback et al. 2008, S. Biba et al. 2010, Steven Biba 2014).
Authors urge the use of Geographic Information Systems for more precise evaluations of the existing footpath network around stops. Vale (2015) suggests improving the node-place model by including the existing footpath network. The model evaluates the quality of a public transport service according to two
Figure 10: Theoretical area within a 700-metre radius around stops and actual accessible area though the footpath network around train and ferryboat stations in the Lisbon Metropolitan Area (Vale 2015, p. 76)
attributes: firstly, the quality of the public transport service available at a public transport hub (node-attribute), and, secondly, the environmental characteristics within a circular area around a public transport hub (place-attribute) (p. 71).
Vale studies 83 station areas in the Lisbon metropolitan area with the help of an advanced node-place model. He calculates a factor from two variables. The first variable represents the area of a theoretical 700-metre radius around each public transport node. The second factor represents the actual accessible area though the footpath network up to a distance of 700 metres from the hub (p. 73). Vale calculates a factor by dividing the area of the 700-metre radius through the area accessible by footpaths. Figure 10 shows the variation of the calculated factors from 0.147 to 0.768. In the worst case, the urban area accessible via the footpath network was only 15 percent of the radial catchment area.
Figure 11: Theoretical and observed catchment areas around Sunnyside light rail stop in Calgary
By adding this relatively simple indicator to the node-place model, Vale showed that dense and diverse urban environments can be very different built realities for pedestrian access to public transport (p. 76). Land use density and diversity are not the only relevant factors for convenient access.
O’Sulivan and Morrall (1996) interview light rail users in the city of Calgary (Canada). They collect data on the departure and origin of all trip legs of the public transport journey from door to door. They calculate the average walking distance to the light rail stop Sunnyside. They correct distance by the average detour factor (as defined in Textbox 3) of the registered walking routes. On a map, they draw a circle around the stop with the radius of the average walking distance. Figure 11 compares this circular catchment area (blue) with the observed catchment area. The observed area derives from actually walked routes (red). This simple analysis shows that the circular and observed catchment areas do not correspond very well.
Characteristics of the footpath network and probably other environmental conditions influence chosen walking routes to the stop, and accordingly deform the catchment area.
Molster and Schuit (2012) consider circular shaped catchment areas as theoretical (1. in Figure 12). Realistically, streets and footpaths around the stop determine access. These footpaths do not always allow access to the stop in a direct line but may require detours. The real catchment area derives from the existing footpath network (2. in Figure 12), as Molster and Schuit define. Further, the individual experienced distance is not an objective measure. The individual perception of distance can vary, as the authors highlight. The real catchment area deforms
Figure 12: Catchment area around public transport stops according to Molster and Schuit (2012)
further with the individual experience of distance to an experienced catchment area (3.
in Figure 12) (p.18-19). How pedestrians experience walking distances to stops can depend on the convenience but equally on the sensory experience of the walking environment. Having to cross trafficked streets certainly appears inconvenient, as the following section discusses.