Definition of movement and activity for transport modelling
Contribution to the Handbooks in Transport: Transport Modelling
Kay Werner Axhausen
IVT
ETH Zürich
October 2006
1
Contribution to the Handbooks in Transport: Transport Modelling
DEFINITION OF MOVEMENT AND ACTIVITY FOR TRANSPORT MODELLING
Kay Werner Axhausen
IVT
ETH Zürich
CH – 8093 Zürich
Abstract
This chapter is proposing a consistent set of definitions of movement and activity against the background of the data needs of transport modelling. The proposed consistent classification scheme for the
movement of goods and persons is based on the concept of the stage, the activity and the reference location or base. Movement is considered as separate from activities at destinations in contrast for example to time-budget studies, where it is just one among many types of activity. The operational definition of the activity is left to the survey designer to suit the needs of the particular study. The chapter
discusses the difficulties resulting from the definition, in particular when aggregating information and
the typical items recorded for stages and activities.
In the second part, the chapter discusses how to translate these definitions into surveys in two steps.
The first step is to define the scope of the survey in detail, in particular the movement and activities to
be reported, so that the universe of the survey is clear. The second step is the choice of the survey approach, the way in which the respondent is guided in recording/recalling movements and activities.
The different possible forms and their limitations are discussed.
Keywords
Movement – Definition – Stage – Activity – Reference base – Scope of movement surveys
1
1
INTRODUCTION
Transport modelling provides the tools to describe and predict the movements of persons, goods and
information in a given or possible future environment. It establishes relations between the amounts,
locations, characteristics and behaviours of persons, firms, infrastructures, services and environments
to calculate flows by time, route, location, mode and service (or often specific aggregates of these
flows) (Ortuzar and Willllumsen, 1994; Schnabel and Lohse, 1997). The data needs vary considerably
by the specific forms that those relations take. There is no place here to discuss the various relations
used (see the relevant chapters below), but they can vary from rough aggregate models of area-wide
flows to detailed agent-based micro-simulations of individual decision makers. Data availability and
modelling approaches constrain and condition each other. For example the assumption that income is
not particularly relevant, will suggest that it should not be asked in a survey, but the known difficulties
of obtaining accurate income information will at the same time encourage modellers to search for relationships without income as a variable. In retrospect, it becomes difficult to decide what came first:
the data difficulties or the modelling idea. Equally, new theoretical insights into the behaviour of the
system elements can spur the search for new data collection techniques and items, while new data collection approaches or technologies can invite modellers to adapt and enrich their approaches (Richardson, Ampt and Meyburg, 1995; Axhausen, 1995).
It is therefore impossible to discuss data needs without reference to the modelling framework to be
supported, although the orthodoxies for modelling and for data collection established by professional
practise or government intervention/regulation seem to suggest otherwise. This chapter has therefore
to select one of these pairings of data collection standard and modelling approach as the background of
its discussion. The discrete choice/equilibrium framework and the personal diary survey, as the current
state-of-the-art modelling/data collection approach-coupling, is a natural choice. The following discussion of the definition of movement and activity will try first to clarify the object of modelling task, but
also second to discuss the difficulties of translating these definitions into survey or observation approaches.
The chapter will next briefly discuss the types of data generally collected in transport modelling to
place the movement/activity data in context. The following section will offer a consistent definition of
movement and activity, while the then next section will discuss some of the specific issues arising in
asking about movements and activities. The final two main sections will address a number of the difficulties inherent in translating these definitions into survey approaches by raising the issue of how to
define the survey object and by describing the various survey approaches currently used.
2
TYPES OF DATA
2
Transport planning draws on the following main types of data for its purposes:
ƒ
Inventories of objects and of their characteristics derived from observation, for example
the location and properties of a road link (starting node, end node, length, number of
lanes, presence of parking, surface quality, gradient etc), the route and characteristics of a
bus service (operating hours, stops served, headways, type of vehicle etc.) or the services
offered by a location (number and type of activities possible, size of facilities, opening
hours, price level, service quality).
ƒ
Census of persons or firms detailing their characteristics obtained from primary surveys
of the persons/firms concerned or derived from other primary sources, such as population
registers, decennial censuses etc
ƒ
Data on current behaviour obtained from observation, in particular counts, or from traveller surveys, frequently referred to as revealed preference data. (RP)
ƒ
Data on traveller attitudes and values provided by the travellers through responses in surveys
ƒ
Decisions and assessments in hypothetical situations/markets obtained from the users
through surveys, frequently referred to in transport as stated preference data (SP)
This set reflects the engineering and economics backgrounds of most modellers and the implicit behavioural understandings of these disciplines, but also the type of decisions, for which transport planning exercises are undertaken. It also reflects the resource constraints of most transport planning studies, in particular during the formative early studies in the 1950’s and 1960’s. In this understanding the
infrastructures and activity opportunities impose generalised costs on the travellers, but offer also utility from their use, which is maximised by the traveller under the constraints of the available household
resources, mobility tools and social time-space regimes (Ben-Akiva and Lerman, 1985). The modelling aims to understand those choices, which are constrained and influenced by the socio-economic
circumstances of the decision-maker, by focusing on the risk and comfort weighted time and cost
trade-offs observable in current or hypothetical behaviour. Recently, there is renewed interest in the
integration of traveller attitudes and values into the modelling of choices, in particular in connection
with the ever growing amount of leisure activities (e.g. Götz, 1998, Gawronski and Sydow, 1999). But
more widely, their inclusion recognises the importance of the social constraints on individual utility
maximisation, or alternatively the importance of the social to the individual (Axhausen, 2005; Larsen,
Urry and Axhausen, 2006). In the same vein, further types of data are being explored, for example information on the size, spatial distribution and contact intensity of the social networks of the travellers,
information on the mental map of the traveller and on the available choice sets, or finally fuller descriptions of network and spatial opportunity structures.
3
DEFINING MOVEMENT AND ACTIVITY
3
The focus of transport modelling is the movement of persons, goods and increasingly the patterns and
intensity of private and commercial telecommunication. Therefore, data collection for transport modelling focuses on the capture of these movements through surveys or observation (counts, but also
more detailed observation of individuals through car-following or GPS-tracing). Movement has to be
defined for observation or survey work to be amenable to measurement. The definition of movement
implies a definition of activity, as shown below. The definitions employed are for professional use, as
they frequently do not match everyday language. They are therefore not necessarily the concepts
communicated to the survey respondents. Here it might be required to use other views of the process
to elicit the desired information. This difference has to be kept in mind by the survey designer.
The following structuring of movements into defined units is internally consistent (see also Table 1 for
the German and French translations of the terms):
ƒ
A stage is a continuous movement with one mode of transport, respectively one vehicle.
It includes any pure waiting (idle) times immediately before or during that movement.
ƒ
A trip is a continuous sequence of stages between two activities.
ƒ
A tour is a sequence of trips starting and ending at the same location
ƒ
A journey is a sequence of trips starting and ending at the relevant reference location of
the person
ƒ
An activity is a continuous interaction with the physical environment, a service or person,
within the same socio-spatial environment, which is relevant to the sample/observation
unit. It includes any pure waiting (idle) times before or during the activity.
.
For the purposes of public transport management and statistics it is useful to add between the stage
and the trip:
ƒ
the customer movement: a continuous sequence of (para) transit/public transport stages of
a certain type ignoring any walking stages undertaken to reach the next point of boarding
caused by transfers.
The customer movement can be defined according to a variety of criteria depending on the purpose, of
which the most important are: by operator, if the purpose is to allocate revenue between multiple operators operating a revenue sharing scheme for a large (regional) network; by type of vehicle, if one
intends to allocate revenue within a firm operating different sub-networks, e.g. between diesel buses,
4
trolley buses, street cars and cable cars; by type of service within a firm or network, e.g. express, normal, night, shared-ride taxi services.
Table 1
Movement defined: English, German and French
Other terms used as
synonyms
Unlinked trip
English
German
French
Stage
Etappe
Trajet, Etape
Customer movement
Beförderungsfall
Trip
Fahrt/Weg
Tour
Tour
Voyage (Deplacement),
mouvements désaggrés
Deplacement, itinénaire, Linked trip
parcours
Circuit
Journey
Reise, Ausgang
Journee
Activity
Aktivität
Activite
Sojourn, round trip
This set of definitions is only one of many possible sets and it is based on a certain understanding of
traveller behaviour and on the demands of surveys of daily mobility and of specialised surveys, such
as those of long-distance or leisure mobility. It also privileges movement by ignoring in the first instance activities undertaken while moving, for example working on the plane, speaking on the telephone while driving etc.
The main alternative is derived from time budget studies, for which travel is just one more type of activity. Those recent surveys, which adopted a time-budget style of approach, were forced to subdivide
travel further to obtain the required detail, i.e. to give special attention to those activities involving
movement. Still, independent of the overall approach there is a need to define the elements of movement consistently. See below for further discussion.
The definition of the stage plus the discounting of activities during movement provides a clear basic
unit for the discussion of movements1. By stressing continuity, while including waiting times, it assures that the number of these units does not become too large. Consider for example, the case of a
train stage, which involves multiple planned and unplanned stops, which otherwise would constitute
separate stages. The limitation to pure idle waiting time allows one to capture any activities associated
with the stages, such as purchasing a ticket or loading/unloading a car, or other activities undertaken
1
Allowing the stage to be subdivided by the activities while moving is possible, but rarely done. A rail traveller
could, for example, record the sequence of activities undertaken: working (reading reports), lunch, leisure (listening to music), working (meeting colleagues).
5
between the arrival in a station/airport/parking facility and the actual departure (e.g. shopping in an
airport store, talking with someone etc.).
While the stage is unambiguous, the definition of the trip depends on the definition of the activity to
provide its start and end points. Depending on the definition of what constitutes an “activity”, it is possible to vary the number of trips, the most frequently used reference unit in transport modelling. The
definition proposed leaves it open, how “relevant” is operationalised by the researcher, respectively
the respondent. The socio-spatial environment is constituted by the persons involved in the interaction
and the environment in which it takes place. In the case of the environment only the type has to remain
the same, for example a walk through a park is within one spatial environment. The definition implies, that any change in the number of persons involved in the interaction defines a new activity, e.g.
somebody leaving early from a joint dinner defines a new activity of the same type, equally the visits
to different stores in a shopping mall are different activities.
Importance can be defined on one, some or all of the main dimensions, by which activities can be classified:
ƒ
Kind of activity: what the person is doing: gardening, talking with someone, operating a
machine, walking through a park
ƒ
Purpose: what the person hopes to achieve in an instrumental sense: earning money, relaxing, getting fit, growing food, satisfying the demand for sleep etc.
ƒ
Meaning: what the person hopes to achieve in a moral sense or say about himself/herself:
helping someone, fulfilling a promise, taking care of himself/herself etc.
ƒ
Project: the greater context of the activity, the framework under which it is undertaken,
e.g. preparing dinner, obtaining a degree, working towards promotion, building a house
etc.
ƒ
Duration
ƒ
Effort accepted to be able to undertake the activity, in particular the detour required to get
to the activity location
ƒ
Expenditure for/income from the activity participation and the associated additional travel
ƒ
Group size and composition
ƒ
Urgency of the activity in terms of the possibility of (further) delay.
This list ignores further more descriptive dimensions, such as for example the number of persons involved, location, kind/type of activity by which the activity could be replaced, the time since the activity has been planned, planning effort, possible time horizons for delays, allocation of costs between
6
participants, allocation of costs between participants and non-participants, satisfaction with the activity
in terms of goal achievement.
While the definition of the trip hinges on the concept of the activity, the definition of the journey requires a reference location. In daily travel this will normally be the (main) home of the respondent.
Still, some travellers will have multiple reference locations (e.g. weekend home, family home and
pied-a-terre of the weekly commuter, student dorm and parents’ house, multiple homes of children living with their parents and stepparents). In addition, tourists on a round-trip will shift their base location between various accommodations during their holiday. In all cases, it seems reasonable to break
any observed tour (from first reference location back to it) into smaller units for analysis. These will
normally be sub-tours of the main tour, but in some cases they involve the shift from one base location
to the next, e.g. the Friday trip/journey from the university town to the parental home. In general, the
researcher will not know about the exact status of a reported location and will have to impose an external definition on the movement data obtained. For example, a reference location is any location,
where travellers spend at least one (two consecutive) nights.
This section has demonstrated the link between the definitions of movement and of activity, in particular, for the aggregates formed from the basic unit stage: the trip, the tour and the journey.
4
TYPICAL ITEMS AND PROBLEMS OF AGGREGATION
At the level of the stage a complete description would involve origin, destination (address/name of location and land use type), arrival time at vehicle/stop, departure time, arrival time at destination, type
of vehicle, type of service, route taken/public transport line, distance travelled, size and composition of
travelling party, cost of movement including any tolls or fares. Arrival time at vehicle and departure
time with the vehicle is normally set to be equal ignoring the times required to load or unload the vehicle and to get it and its passengers ready for departure. This frequent lack of differentiation requires
the estimation of any waiting times for public transport services. Routes taken are mostly added from
network models and are not directly surveyed, in spite of many positive experiences with this approach. Distance travelled is estimated by the traveller, if required.
The clock times recorded by the travellers tend to be rounded to the nearest 5 or 10 minutes. The resulting calculated travel times are rounded as a consequence. Such rounding can also be observed for
distance estimates and stated travel times, but less so. Many local and regional surveys therefore re-
7
place respondent answers by estimates from network models for the further work with the data (See
Chalasani et al., 2005 for the accuracy of such estimates). They sometimes drop some of the items
from the survey altogether. National surveys were not able to do so, because they lacked the necessary
network models. Today, geocoding of all addresses is possible and advisable. For descriptive analyses
only the respondent answers should be analysed, as network models impose a non-existing uniformity
on the travel times, which in reality depend on a wide range of factors not captured by such models
(detours, service disruptions, deliberately slow/high speeds, parking search, time taken to load and
unload the vehicle etc.). For non-motorised modes current networks are normally not fine enough to
give credible estimates. While network model estimates of travel times should not replace the original
data for descriptive analysis, they should be used to cross-check the responses and to prompt additional queries of the respondents, if necessary. In the context of choice modelling one can consider the
replacement of respondent answers with network estimates to have the same error distributions for all
alternatives, but one has to consider to what extent the assumptions of the network model bias the results, especially the assumptions used for the calculation of the generalised costs of the different routes
and the assumptions used for the modelling of peak formation and spreading.
For distance estimates the case is stronger to replace respondent answers with network estimates, as
the respondent estimates have known patterns of distortion (Bovy and Stern, 1990; Chalasani et al.,
2005). Still, one has to be sure of the quality of one’s network model to do so. In the case of walking
and cycling many of the off-road connections available are not included in the networks distorting the
calculated shortest paths. For all modes deliberate detours, for example due to parking search, cannot
be modelled, again distorting the calculations. In any case, a respondent estimate is a useful item
within the survey, as it can be used to cross-check inconsistencies between the distances, locations and
times given. It can also be used to improve the coding of destinations, when the respondent cannot or
do not provide a full street address.
Common to most modelling approaches are the following activity characteristics: type precoded normally with a mixture of purpose and kind of activity -, location, size of party, parking fees, arrival
time at the activity location, starting and end time of the activity. In most transport surveys, the actual
starting time of the activity is not obtained from the respondent, so that the waiting times are generally
unknown. Depending on the model approach many further characteristics could be added (see above).
A curios omission in most surveys is the lack of information about the expenditure during/for the activity, which would be a useful indicator of its importance.
Survey practice in transport has tended to employ relatively crude classifications, which mix the kind
of activity with its purpose, while ignoring the remaining dimensions. Typical classifications are:
8
work, work related, shopping, private business, leisure, dropping someone off/picking someone up,
escorting and an open question for any other activity type. A classification of this type communicates
an interest in longer activities, mostly those involving earning money or spending it, or those involving firm commitments or strong role expectations. Dropping off/picking up falls also in to this category, considering the frequently lengthy detours required, sometimes furthermore involving prior collection of other persons; e.g the school run with children from different households. This level of detail reflects both the past preoccupation with the morning commute as the transport problem, but also
an assessment of what a respondent will put up with during the survey. More detailed classification
schemes, though in the past mostly administered to highly motivated respondents, which have frequently produced higher numbers of reported trips then the more standard classifications. Clearly,
each modelling exercise has to find its own balance between the level of detail desired to test behavioural hypotheses and the ability and willingness of the respondents to answer. Equally, any comparison of trip numbers has to keep this priming effect of the activity classification in mind: a time budget
survey with hundreds of activity classes should produce a different number of trips in comparison with
the typical travel survey and its single digit number of classes (See for example Armoguum et al.,
2005 or Madre et al. (forthcoming)).
The problem of aggregation from stages to trips and from trips to tours/journeys is acute for those
variables, which cannot be added together: mode and activity class. While size of party, the times, distances, speeds can be added/averaged, a main mode/activity class has to be determined based on predetermined rules, as information about the subjective importance is generally missing. Typical rules
for the determination of the main mode use either numerical criteria, such as mode with largest share
of the distance travelled, with longest duration or with highest speed, or hierarchies of the assumed
strength of the mode to shape the movement, for example air plane – train – coach – underground –
LRT – bus – car – bicycle – walking. The same types of rules are applied when one needs to determine
the main activity class of a tour/journey.
As a result, those rules should be reported in conjunction with any results. The impact of this aggregation has to be kept in mind, when comparing results from different surveys. Luckily, in most cases the
impacts will be small, as single mode trips/journeys dominate in many countries.
A related problem of aggregation occurs, when counting the number of movements at different levels
of social aggregation: for example: person – (family unit) – household. Joint movements, for example
for leisure purposes, mean that for example the number of household trips can be considerably smaller
then the number of person trips: a joint car trip with three household members would count as three
9
person trips and one household trip. The analyst has to decide, which type of trip is the one relevant to
model. The same attention has to be given to the aggregation by vehicle used.
5
DEFINING THE SURVEY OBJECT
The totality of movements, which could be the subject of a survey, is normally not surveyed. Each
survey decides to exclude certain types of movement as irrelevant to its purpose. Some of these exclusions have become so ingrained, that they are rarely if ever discussed, but it is good practise to account
properly for such exclusions by spelling out the survey object in detail. This also helps in the process
of designing the survey, especially the choice of the overall approach used to guide the recording/recall of the respondent.
The definition has to specify the following aspects:
Target movements
Define the movements, which are within the scope of the survey
but for the exceptions below
Base unit
Stage, customer movement, trip, journey
Activity definition
Characteristics of an activity, which needs to be reported
Reporting period
Interval from a specified starting time for which the movements
should be reported.
Minimum distance
Size of any lower bound for the distance covered
Minimum duration
Size of any lower bound for duration
Spatial exclusions
Definition of any spatial exclusions
Temporal exclusions
Definition of any temporal exclusions
Spatial resolution
Maximum allowable size/type of a destination location
Reference location
Definition of the base or reference location
Typical examples of such definitions are shown in Table 2 for three possible surveys: a survey of daily
mobility, a long distance travel survey and a tourism survey. The definitions show typical choices for
the definitions. Note the interaction between the target movement definition and the activity definition
and the thereby accepted reduction in the number of reported activities and trips. Note also, that while
10
the exclusion of walk-only trips in the example is common, it is not recommended practice as such
short trips are important elements of the day.
Table 2
Examples of possible survey object definitions
Daily mobility survey
Long distance
survey
travel Tourism travel survey
Target movements
All relevant stages dur- All relevant trips during
ing the reporting period the reporting period,
which are part of a
journey to a destination
at least 100 km from the
reference location .
All relevant journeys,
which either involve a
destination more then
100 km from the reference location or at least
one overnight stay
Base unit
Stage
Journey
Activity definition
Any interaction longer Main activity, which Main activity, which
then five minutes, un- has motivated the trip to motivated the journey to
less a “serve passenger” the destination
the main destination
stop
Reporting period
One day starting at 4:00 Eight weeks, starting Four weeks, starting
am until ending the day Monday 4:00 am of the Monday 4:00 am of the
at the reference location first week
first week
Minimum distance
Walks over 100m
None
None
Minimum duration
None
None
None
Spatial exclusions
Stages which are part of
trips within a closed
building or compound,
such as factory or office
campus;
Trips which are part of Journeys within destinajourneys to destinations tions
less then 100 km from
the reference location;
Temporal exclusions
Stages undertaken as
work while working,
e.g. driving a delivery
vehicle
Trips undertaken as None
work while working,
e.g. driving a charter
coach bus
Spatial resolution
(Building) address
Municipalities or sepa- Municipalities within
rately identifiable set- the national boundaries,
tlements, e.g. resort countries elsewhere
complexes,
villages,
which are part of larger
administrative units
Reference location
Home address within Destinations, where the Destinations, where the
the study area
traveller spends at least traveller spends at least
two consecutive nights one night
Trip
Trips
Stages starting or end- tions
ing outside the study
area during the reporting period
11
within
destina-
TRANSLATING THE DEFINITIONS INTO SURVEYS
6
The definitions proposed structure the movements/activities of the respondents into units chosen by
the researcher. Most of these definitions cannot be directly used in survey questions. The survey designer has to find a way of guiding the respondents in their recording/their recall in such a way, that
the desired information can be obtained from the answers. In the design, the researcher has also to
consider, that the respondents limit the amount of effort they spend on surveys and that their memory
limits their ability to recall certain details. Each of the different approaches uses a different dimension
of the activity/movement stream to guide the respondent (Axhausen, 1995) and to stimulate their recall:
-
Stops (destinations), the points with a particular land use where a movement ends, are
highlighted in the stage approach. The characteristics of the activities following the arrival at a destination are established in addition to the stage details. Arrival times at the activity location and activity duration (including any unknown waiting times) are derived
from the stage times.
-
The movement to the next activity is stressed by the trip approach, in which the stages
are not necessarily identified by sequence, although it is usual to ask for all modes used,
maybe including the travel times with them. The coding of the activity is normally restricted to seven to ten categories, but open categories for other and for leisure are well
accepted by the respondents and allow more detailed coding during analysis. Arrival
times at the activity location and activity duration (including any unknown waiting times)
are derived from the trip times.
-
The sequence of activity episodes is at the centre of the activity approach, which inverts
the trip approach, but does not necessarily offer a more detailed coding of activities. This
approach can cover activities at the destinations, in particular at home, by appropriate
prompting of the respondents. The movement details are covered with a specialised set of
items, when relevant. The starting times of the trips and the trip durations (including any
unknown waiting times) are established from the activity times. Stages can be established, if the respondents are suitably prompted.
-
The flow of activities is covered by the time budget approach, which invites the respondent to classify each 10/15/30 min interval of the day by the activity undertaken (Szalai,
1972; As, 1978). The coding is open and the respondents refer to detailed coding lists for
this purpose. The activity and movement episodes addressed in the first three approaches
are recovered in post-processing. This approach does not normally establish the movement details required for transport modelling, but it is not impossible in principle to do
so, especially with modern computer-based survey instruments. Very short trips can get
lost, if longer intervals are chosen for the roster.
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Each of the approaches has its strengths and the designer has to choose against the background of the
study objectives. Research so far does not allow to say, if one of the approaches is superior to the others in terms of data yield or unit and item non-response. British and Australian surveys prefer the
stage-based approach, while numerous recent North-American surveys have adopted an activity-based
approach. Continental European surveys employ in the main trip-based approaches, in spite or just because of the large share of public transport trips normal there.
In each case, the higher level movement concepts – (trips), tours, journeys – have to be established
during the post-processing of the data. Equally, the stages have to be constructed in all but the stagebased approach, based on the information available from the answers of the respondents and external
information, e.g. network models. These post-processing steps have to be documented in the reports to
allow better comparison of different surveys.
7
FREIGHT AND COMMERICAL TRAFFIC
In an era, when just-in-time delivery is becoming the rule for commercial deliveries and will become
the rule for domestic deliveries due to the demands of internet ordering good data on the amount, type
and kind of commercial traffic is crucial. Freight data collection has been neglected by transport planners in the past, as they were concentrating on the morning peak, during which commercial traffic was
less important. For example, in many daily mobility surveys movements undertaken by car/truck as
part of work by truck drivers, postmen, craftsmen, are excluded to reduce the response burden, but
also as out-of-scope.
The conceptual framework proposed above applies equally to the collection of the necessary data for
freight and commercial traffic at the three possible units of concern: the individual parcel, the vehicle
and the driver. It is clear that different decision makers have different concerns: e.g. the regulator of
traffic safety might wish to know about the work load of truck drivers (working hours, number of delivery stops, amount loading and unloading etc.); the manager of a delivery service might wish to
know about the “stages” of a parcel (timing, waiting times, number of unsuccessful delivery attempts,
location of pickup and delivery locations, price charged etc.); the urban transport policy maker might
wish to know about the trips of a delivery truck (timing, routes, destinations, degree of loading, type of
goods delivered). Freight and commercial vehicle information can be obtained from the firms operating the services/vehicles, if their co-operation can be obtained, although in particular cases it might be
better to obtain the information from the driver or the parcel (independent tracking). The development
13
and wide-spread adoption of parcel and vehicle tracking systems by many freight operators/service
providers makes it possible to obtain most information needed for transport planning from these systems. They are a combination of GPS/cellular phone-based vehicle location tracking plus reading of
tags attached to parcels or containers at each stage of the journey2. For firms without such systems it
is necessary to develop special implementations for survey purposes (e.g. Batelle, 1999). This might
also be necessary, if detailed information on the routes chosen is to be collected, which might not be
extractable from the firm’s system.
Next to recording the freight and commercial flows from the perspective of goods delivery, transport
planning could record these from the perspective of the customer; the “commercial trip attraction” in
the traditional terminology. This is work which still needs to be done.
SUMMARY
8
This chapter had the task of proposing a consistent definition of movement and activity against the
background of the data needs of transport modelling. The proposed consistent classification scheme
for the movement of goods and persons is based on the concept of the stage, the activity and the reference location. Movement is considered as separate from activities at destinations in contrast for example to time-budget studies, where it is just one among many types of activity. The operational definition of the activity is left to the survey designer to suit the needs of the particular study. The chapter
discussed the difficulties resulting from the definition, in particular when aggregating information to
higher levels and the typical items recorded for stages and activities.
In the second part, the chapter discussed how to translate these definitions into surveys in two steps.
The first step is to define the scope of the survey in detail, in particular the movement and activities to
be reported, so that the universe of the survey is clear. The second step is the choice of the survey approach, the way in which the respondent is guided in recording/recalling movements and activities.
The different possible forms and their limitations are discussed.
2
Tags can be for example bar-coded labels or various forms of active or passive electronic tags. In the case of
railroads the boundary between container and vehicle blurs and it is possible to use stationary beacon-based tags
to locate the container/vehicle/wagon. Similar technology is used by public transport operators to trace their vehicles.
14
9
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Armoogum, J., K.W. Axhausen, J.-P. Hubert and J.-L. Madre (2005) Immobility and mobility seen
through trip based versus time use surveys, Arbeitsberichte Verkehr- und Raumplanung, 332,
IVT, ETH Zürich, Zürich.
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