A New Approach to Generation of Household Activity-Travel Pattern: A Modelling Framework and Study Results
Siamak Khorgami, AECOM
Operational activity-based models have been developed and are being used in North America and some mainland European cities for policy analysis. Closer examination shows that most operational models do not fully embody the principles of an activity-based approach. In particular, (i) the models mainly concentrate on out-of-home activities, (ii) they assume that only one activity takes place at each non-home location, and (iii) the basic unit of analysis in these models is the trip tour or the activity pattern, rather than using individual activities as the basic building blocks.
This paper first identifies the key concepts behind a fully activity-based approach and then introduces a framework which outputs daily activity/travel patterns, using individual daily activities as the starting point. The paper presents in more detail the results of calibrating the activity generation and household allocation model system on weekdays, using data from the 2001 UK Time Use Survey (TUS). Scheduling sub-model framework has been examined examined by using data of transport network and available facilities.
Activity based travel analysis has received much attention in the academic literature and has seen several practical applications in recent decades. Operational models have been developed and are being used in North America and some mainland European cities for policy analysis; although in the UK the practical application of activity-based modelling is much more limited, despite the fact that available sources of travel and activity data enable such models to be developed.
However, closer examination shows that most operational models do not fully embody the principles of an activity-based approach. In particular, (i) the models mainly concentrate on out-of-home activities, (ii) they assume that only one activity takes place at each non-home location, and (iii) the basic unit of analysis in these models is the trip tour or the activity pattern, rather than using individual activities as the basic building blocks.
The proposed model has two major sequential components: (1) an activity generation and household allocation model system, followed by (2) an activity/travel scheduling model system. The introduced conceptual modelling framework (Khorgami, 2012) is examined by using data from the 2001 UK Time Use Survey. Firstly, the paper presents the results of calibrated activity generation and household allocation model. Then, a modelling framework for activity scheduling is introduced which allows for multiple activity engagement per destination.
The model system starts by using the socio-demographic and locational characteristics of household members, and individual employment status (full-time, part-time, student, retired, non-worker), to estimate work/study duration, approximate starting time and time spent travelling to/from work/study. Household care and family maintenance activities are then modelled; these are assumed to be in-home activities and include food preparation, childcare, care of dependent adults, etc. An individual’s basic needs are modelled next, in the form of personal care activities, including sleeping and eating. While undertaken by everyone, the activity duration is influenced by personal characteristics (e.g. age), household structure (e.g. presence of young children) and primary roles – in particular time spent in employment and commuting to/from work.
The remaining activities include those associated with household maintenance that take place out-of-home (e.g. escorting household members, shopping & services) and discretionary activities, primarily social and leisure activities. These latter activities can take place either at home or outside the home, so a trade-off sub-model for time allocation to in-home and out-of-home duration of activities is developed. For these discretionary activities, a range of explanatory variables is included in the choice model, including lifestyle and socio-demographics of the household and individuals, accessibility to services, accessibility to transport (car and public transport) together with the availability of facilities at home (e.g. access to the Internet).
Many types of activity episodes may be carried out jointly with another household member or alone. The joint activity engagement component of the modelling system focuses on two-adult households (with or without children) and identifies the joint activities in their schedules.
A range of analytical techniques have been used to develop the activity generation component of the modelling system, including discrete choice modelling, Monte Carlo simulation and hazard duration models. This component outputs information to the second stage activity/travel scheduling model in terms of the number and duration of activity episodes, by type of activity, and incorporates a check to ensure that the 24 hour personal time budget constraint is met.
The proposed approach allows for engagement in multiple activities at non-home destinations. The assumption, embedded in activity/travel models, that travellers engage in only one activity at each non-home stop, has been questioned ( Khorgami et al., 2010). Results of the analysis show that some individuals engage in more than one primary activity while at a non-home stop On average, individuals take part in more than one primary activity at 20% of stops, and the mean number of primary activities per stop for the total adult sample on weekdays is 1.26, when using seven activity/trip purpose categories. A modelling framework for scheduling sub-model has been developed and examined by using a transport network and available facility data.
Further, intra-household interactions are taken into account through modelling the possibility of engaging in joint, independent, and joint and independent activity episodes.
Khorgami, S., (2012), A Comprehensive and applied approach to analysis and modelling of household activities using UK time use data, European Transport Conference, Glasgow, Scotland
Khorgami, M. H., Jones, P., Titheridge, H. (2010) “The validity of assuming only one activity per out-of-home location in activity-based demand models constructed from trip-based survey data”, In the proceeding of 12th World Conference of Transport Research (WCTR), Lisbon, Portugal
Association for European Transport