2 Explaining and predicting travel behaviour: Theoretical review and
2.4 Activity and transport mode interdependencies: A framework for analysis
mapping the access and egress catchment and the geographical extent of diff erent routes (together with their travel time) conveys relatively little information about the possibility of an individual making use of public transport. As illustrated by Lenntorp (), Forer and Kivel () and Dijst et al. (Dijst et al., ), accessibility is not solely dependent on the access and egress travel time, total trip time or accessibility of the system, but also on whether individuals – specifi cally those constrained by transport mode availability – can implement their activity programmes. Defi ning more ‘feasibility’ measures, such as the interconnectivity ratio, may further help to improve the assessment of public transport as an available transport alternative.
Ultimately, what is required is a more systematic eff ort to take into consideration the derived demand for travel and how this demand is satisfi ed by the public transport system. is approach should take into explicit consideration the relationship between activity and transport choice facets as outlined above. Such an integrative framework is presented in the following section.
– the home-based tour (or multi-sojourn travel), becomes an important structuring element in daily structuring element in daily structuring element activity travel behaviour. e combination of fi xed locations and the obligatory nature of work has resulted in the work-tour becoming the predominant tour around which daily activity-tour around which daily activity-tour travel behaviour is shaped (Kondo and Kitamura, ; Nishii et al., ). Not surprisingly, many researchers have pointed to the secondary role of the work-tour, i.e. a tour to which other activities are linked (or chained). Simple work-tours refer to home-based tours on which no additional activity is inserted, while during complex work-tours, intermediate activities may be inserted before, during and after the main work activity. Figure - shows this distinction.
e formation of complex chains is arguably a function of all the causal elements shown in Figure - (i.e. activity demands, land-use, urban form and transport system, and the interaction among these). e urban structure and the associated public transport system (route structure, modes, stations, etc.) represent the fi xed spatial environment within which an individual operates. Given the longer-term choices of work and residential location, the spatial environment is assumed given. As stated in Section ..., the combined eff ect of the urban structure and the public transport orientation, is bound to impact on tour formation decisions. As shown, public transport tour trips to and from the central business district and between central business districts as well as trips aligned in highly urbanised corridors are more feasible as a result of service and network orientation and higher service frequency. In e Netherlands at least, the central business districts are characterised by a very high density and diversity of retail and service industries, as well as a high-quality public pedestrian environment.
Trips terminating and commencing from the central business district therefore provide more opportunity for trip chaining. Clearly then, work-tour formation decisions are infl uenced by the urban structure, the transport system and the trip orientation.
However, for public transport to be included in the work-tour mode choice set, the mode needs to provide, among others, adequate acceptable proximity (access and egress), connectivity (number of transfers) and interconnectivity (access and egress as a share of total trip time).
While proximity and connectivity requirements are relatively well established, less attention has been paid to interconnectivity. Although the relative share of access and egress is important, surprising little research has addressed this issue; research has tended to focus on access and egress as part of out-of-vehicle time (OVT) considered as a relative share of IVT (Koppelman,
; Krygsman, ; Kurth et al., ; Liu et al., ; e Central Transportation Planning Staff , ; Wachs, ). Very few studies have quantifi ed access and egress times as a ratio to total travel time. eoretically, the relationship holds implications for the propensity to use public transport. Wachs () postulated that, as access (and egress) distance increases relative to total trip distance, the disutility of continuing to the fi nal destination with the access mode decreases relatively to the need to stop, fi nd parking, wait and transfer on the main mode¹⁴.
is relationship not only holds for inter-urban traffi c but also for intra-urban travel where, in e Netherlands, public transport competes with bicycles (and even walking) and where access and egress may comprise a signifi cant contribution of total trip time. In the context of this relationship between tour transport mode choice and activity scheduling on the tour, misrepresentation of the transport environment may lead to serious inaccuracies in representing the possibility for activity engagement on tours and exploring the reciprocal and interdependent nature between activity and travel choices (Gärling et al., ).
An important question from a transport policy perspective is how the transport mode infl uences daily activity and travel behaviour and tour formation in particular. Various activity and public transport travel behavioural adjustments can be postulated: the longer time and distance associated with public transport reduce space-time autonomy, resulting in fewer activity engagement possibilities (Miller, a)¹⁵; the increased accessibility conditions of locations and the multifunctional land-use around, for example transfer locations, might increase activity engagement possibilities (Arentze et al., ); public transport travellers are faced with asymmetric mode availability and have to change modes, which might impact on location and activity-scheduling behaviour. As Lenntorp and Forer and Kivel illustrated in their time-space approach, there are clearly interdependent relationships between transport mode decisions and activity decisions (Forer and Kivell, ; Lenntorp, b). Flexible transport modes (in time and space) will allow more activities to be scheduled on the tour (as a result of allowing a larger action space) while infl exible transport modes restrict complex tour formation. Clearly, the short-term tour formation decisions should be analysed from an activity-based perspective, taking into consideration all the (given) long- and medium-term relationships.
Assuming that public transport is included in the work-tour mode choice set (i.e. it is available and provide acceptable interconnectivity), the relationship between transport mode choice and
Figure -: Daily time-space path of car and public transport traveller
6:00 9:00 11:45 12:30 15:00 17:00 19:0019:30 21:00
v v
Car Public TransportPublic TransportPublic T
T1 Earliest possible time that worker can leave base location T2 Latest arrival time mandatory activity
Tx Tx
T =T2-T1Morning commute travel time interval
T3 Beginning of free time window during mandatory activity T4 End of free time window
Ty Ty
T =T4-T3Lunch time interval
T5 Earliest possible departure time at mandatory activity T6 Latest arrival time at home location
Tz Tz
T =T6-T5Evening commute travel time interval
T7 Earliest possible departure time from home location T8 Latest arrival time at home location
Tw Tw
T =T8-T7Evening home free time interval L1 Location of home
L2 Location of work T8
L=L1-L2
v
T7
T5
T4 T3
T2
T1
6243
Distance between bases
Speed of the travel mode the worker uses Maximum activity duration: h=T-L/v
Parameters of Daily Time-Space Path Time
L1 L2 Urban Space L1 L2
activity-chaining propensity can be conceptualised with reference to Figure - (Gärling et al.,
; Jones, ).
e fi gure traces an individual’s hypothetical daily time-space path (or trajectory) between home and fi nal destination (e.g. work). e daily path consists of connected prisms – indicative of activity engagement possibilities – and vectors indicating travel (Forer and Kivell, ;
Hägerstrand, ; Lenntorp, a). e parameters of this daily activity-travel path are shown at the bottom of the fi gure. A typical worker using the car as primary tour mode has three prisms, i.e. before work, after work and in-between work, during which activities can be inserted on the tour (a fourth prism is one after returning home).
As discussed, public transport constrains individuals to routes and points (transfer locations), inhibiting their ability to use the entire volume of their theoretical prism construct. As a result, the time-space daily prism path shaped by public transport is, contrary to that of unimodal transport alternatives, a construct of smaller, connected prisms (i.e. the access, transfer, egress and lunch-time prism). Activity engagement is thus primarily a function of access and egress (and transfer) prisms and the in-between work prism. e in-between prism, however, is constrained by the asymmetric mode available: public transport users do not have access to private modes (with the exception of the bicycle and walking). As Figure - shows, individuals using public transfer forfeit spatial and temporal autonomy, and as the geometry of time-space prisms are indicative of the possibility to insert intermediate activities, public transport users are at a clear disadvantage. e choice of main tour mode will thus very much infl uence the main tour mode will thus very much infl uence the main tour mode probability and
probability and
probability location of intermediate activities, i.e. before, in-between and after (Burns, ).
is possibility to insert additional activities on the work-tour, however, is not only a function of transport modes but, equally important, also a function of individual and household characteristics (Kwan, ; Kwan, ). As illustrated by Lenntorp () and Kivel and Forer (), some individuals are very constrained by their activity demands and the spatial and temporal profi le of their activities. Individuals facing complex activity programmes will arguably face much time pressure and be more inclined to form complex tours to save travel time. Some household tasks such as child-care responsibilities coupled with work requirements might increase the propensity to form complex transport chains. Constraints, in the form of limited time, opening hours of facilities and long working hours, however, also impact on work- tour formation decisions. us, diff erent individuals may refl ect very diff erent accessibility requirements, which again impacts on the transport mode decision. As a result, in addition to the transport mode properties, the activity-based approach requires that the individual’s activity programmes (activity demands), household attributes and interdependencies, as well as any constraints impacting on the individual and travel and activity engagement, also be considered when exploring tour formation decisions.