A Holistic View on Transportation of People

Transcription

1 A Holistic View on Transportation of People Author: Stig Franzén, PhD Executive Director ARISE-FRANCON Chalmers Science Park, SE GOTHENBURG, Sweden Phone: ; Fax: , Abstract By combining a cognitive s engineering approach, existing models for ation s analysis, and relevant theory elements of both dynamic control and communication s and human-machine s, a conceptual (and ideal) model and an analytical framework for public ation have been developed. The s approach applied in the model and the framework includes a hierarchy of functional levels describing five processes in public ation, i.e. the accessibility, the travel, the, the traffic and the motion s and their dynamic interrelationships. The use of the model and the framework as a tool for design, analysis and evaluation of public ation solutions has been validated by its application in the Gothenburg context including the technical platform for information and communication - the KomFram. The Gothenburg example shows that the introduction of new information and communication technologies in a ation process can create new but also challenging possibilities related to both public and private means of. The implementation must be carried out with great care as new or further developed old functions and s will have large impacts on all types of actors found on all abstraction levels in the ation process. Especially the decision-making process will become more distributed and more demanding on the human actors. It is therefore discussed how the user requirements for solutions for ation of people no longer can be focused only on the end users (mainly identified as travellers and/or passengers), but must take into account all types of actors and actor groups. Transportation of people must be put into a wider context and a holistic view, based on the model and the framework, must be introduced to support the analysis, design and evaluation of new ation measures to make certain that the most urgent policy objectives in urban environments are met.

2 1 Introduction The strong need to improve ation of people in urban environments has most notably been demonstrated in efforts to change the modal split of from private to public means. Society is faced with problems like traffic congestion, air pollution, limited accessibility as with more general policy issues related to different aspects of quality of life and of the "sustainable city of the future (Sjöstedt 1994, European Commission 1994, CEC 1996, EuroCASE 1996). For such a future development in passenger to occur it is most important that the attractiveness and quality of the travel and services made available by public authorities and organisations increase. Quality measures in public ation can be defined in several ways and many definitions are found in literature. Some elements are almost compulsory in all definitions like regularity, reliability, delays in traffic, quality of the shelters at stops and of vehicles used, and finally static information material at stops, at home or at work. Dynamic information services have recently been introduced in many cities and provide real-time information on predicted arrival or departure times at stops as well as, in some rare cases, advice for travellers and passengers when incidents occur in traffic and, as a consequence, the travel and services are disturbed. Many R&D activities have been conducted in this area, but so far few concrete results from real implementations are made available. The main reason is the present lack of a highly sophisticated and costly infrastructure for communication and information processing. However, the Gothenburg Traffic and Public Transport Authority (Trafikkontoret) started work in this area already in the late 1980s. Then the first ideas and concepts of an information and communication platform with the main purpose to help improve the mobility in the city were presented. Since then the GoTiC Research programme has started (Franzén et al 1994) and a user-oriented s approach to public ation has been developed and applied in research activities as well as in the development and implementation of new functions (GoTiC Research ). The mass passenger situation of today puts forward the main question of how, with limited financial resources, a complex for public ation should be designed and developed in order to provide attractive travel and services to citizens and visitors in the urban context concerned. Several problem areas have to be addressed but the most important one is the design process itself, especially as modern information and communication technologies have made it possible to design and implement new and advanced support s for different types of actors. Systems design is mainly concerned with the general structure of public ation as a whole but more specifically with the need to develop and establish an improved understanding of public ation, focused on the characteristics of actors, actor groups and their roles, responsibilities and dynamic interaction. Different types of actors are found in mainly decision-making roles and examples are drivers, traffic control operators, passengers/travellers, administrators and politicians. 2

3 2 A s approach to public ation By combining a cognitive s engineering approach (Rasmussen et al 1994), existing model approaches for ation s analysis (Manheim 1979, Sjöstedt 1994, EuroCASE 1996, OECD 1996), and relevant theory elements of both dynamic control and communication s and human-machine s, a conceptual (and ideal) model of and an analytical framework for public ation (focusing on mass passenger ) for the design and evaluation of public ation solutions have been developed (Franzén 1999a). In other words, a s approach to public ation has been introduced (figure 1). DECISIONS NOT TO TRAVEL PRIVATE TRANSPORT OPTIONS ACCESSIBILITY SYSTEM TRAVEL SYSTEM INDIVIDUAL GOALS, PREFERENCES, NEEDS, CONSTRAINTS, ETC. Traveller(s) PUBLIC TRANSPORT OPTIONS REPLANNING REQUESTS Passenger(s) Info 3 TRANSPORT SYSTEM TRAFFIC SYSTEM Politicians, administr., planners, owners, etc. RESOURCES, TIME TABLES, ROUTES, ETC. Transport organiser Traffic control MOTION SYSTEM Drivers, vehicles, network elements STATES OF SYSTEMS SOCIETAL GOALS, VALUES, NORMS, BUSINESS GOALS, RESOURCES, ETC. Info 1 Info 1 Info 2 Info 4 DISTURBANCES Figure 1 The ideal public ation process seen as a hierarchy of functional levels (Franzén 1999a). It is important to further clarify the use of the terms process and in relation to the conceptual model in figure 1. The term is used to describe each one of the functional levels as they are composed, emphasising both the structure and the specific elements included. The term process is used to describe the dynamic interaction between elements one every functional level and the relations between the functional levels can be described as a hierarchical structure. From a process perspective, a found on one level in the hierarchy (the controlled ) is (on the next higher level) dynamically controlled by a controller or a decision-maker using information and data collection (a sensor ) and processing in order to closed the feedback loop. From a structural point 3

4 of view these elements (the controlled, the controller and the sensor ) form another but on a higher functional level in the model. In the model in figure 1, the hierarchy of functional levels reflects five dynamic processes (the accessibility, travel,, traffic, and motion processes) to be found in public ation. The structure of the hierarchy is composed of five closed-loop control s, each one related to the five processes as indicated above. The elements of each control are seen as either being nodes for decision-making and actions (controllers and actuators), for information collection and processing (sensors or measurement s) or links for data and information flows (the corresponding control elements are listed in brackets). In order to further highlight the structure and the related elements, the traffic process of the model is presented in a slightly different way in figure 2. VEHICLES OUT OF ORDER NETWORK ELEMENT BLOCKED (7) VEHICLES AS IN LINE AND TIME TABLE INFO (1) TRAFFIC CONTROL (OPERATOR(S)) (D) TRAFFIC CONTROL CENTRE COMMAND(S) (5) DRIVER(S) OF VEHICLES (E) HANDLING AND MANOEUVRING (6) MOTION SYSTEM (A) ACTUAL VEHICLE POSITION AND TIME VS. LINE (2) (4) VEHICLE POSITION AND TIME VS. LINE (DERIVED) VEHICLE INFO INTO LINE INFO (C) (3) INDIVIDUAL LOG OF A VEHICLE S POSITION/TIME DRIVER(S), (AUTOMATIC) VEHICLE LOCATION (B) (The numbers and letters refer to entries in table 1) Figure 2 The traffic process presented as a closed-loop control process (Franzén 1999a). The basic coupling between the different functional levels of the model can be seen as a means-ends hierarchy. For instance, the control actions in the process (to match the demands with options - WHAT should be done) can be seen as the reference value of the traffic process (vehicles should follow time table information - the goal, i.e. WHY) but also as the actuator output of the travel process (HOW the means for travel are identified). This can also be explained as when the same variable in figure 1 in viewed from different process perspectives, and then functionally in a control theoretic framework has different meaning depending on what level in the hierarchy is addressed. In table 1, three of the processes are highlighted and reference is made to figure 2 and the related terminology of closed-loop processes and the means-ends relations mentioned above can be identified in the corresponding table cells. 4

5 Table 1 Closed-loop control process elements related to elements of three public ation processes (from Franzen 1999a) closed-loop control process traffic process process travel process A controlled motion traffic B C D E sensor processing controller or decision-maker actuator driver(s), (automatic) vehicle location time and pos. info of vehicle into line info traffic control centre (operator(s)) driver(s) of vehicle(s) (passenger(s)), (automatic) vehicle location identifier of options organiser, (passenger(s)) traffic control centre (operator(s)) (automatic) vehicle location other sources Information officer(s), support s collective of individual traveller(s) organiser, (passenger(s)) preferred states (reference values) actual states (controlled variables) collected data (sensor output) calculated or extracted information control actions (decisions) actuator output (influences) disturbance(s) (uncontrolled inputs) vehicles as in line and time table info actual vehicle position and time individual log of a vehicle's position/time vehicle position and time vs. line (derived) traffic control centre command(s) handling and manoeuvring by driver(s) vehicle(s) out of order, network element blocked options needed are available available real-time options vehicle flows on lines/routes in network existing options matching of demand/supply traffic control centre command(s) traffic flow(s) in network hindered realisable travel plan (links) travel plan links vs. options available real-time options missing travel plan links and alternatives travel plan links vs. demands matching of demand/supply option(s) missing With reference made to figure 1 (and where relevant table 1) the five processes and the most important functions involved can be identified and described. The process related to the highest functional level is the accessibility process - a process in which the controllers are politicians and/or administrators and where the actuators are the travellers and/or the organiser. The preferred states (or reference values) of the controllers in this process are rather complex and must be included as political agendas, policy objectives, etc.. This level is also necessary in the model, as the available resources will be determined on this level and therefore influence what type of travel and services can be realised in practice. On the next level of the hierarchy, the travel process is identified and here an individual perspective is applied. The reason being that the controllers are the travellers themselves, and the controlled variables are linked to the intended movement of people and the result is their individual travel plans - or in other words the actual matching of travel plan links with available options. In the ideal case the travel plan is created with respect to both 5

6 societal and individual goals (the individual goals dominate) as related to existing options (both private and public). The travel plan (and its links) is translated into a chain of demands for options (often multimodal) - and a replanning will occur if a option is missing or, in other words, when a disturbance has occurred in the or traffic s. Any replanning activity is depending on feedback from the disturbed s and is exemplified by the block Info3 in figure 1. The output from the block Info3 is also distributed to the passengers, the passengers being a central actor in the process found on the next functional level. The passenger is defined both as a passive "object to be ed" and as an active element in the production of the service - for instance when entering and exiting a vehicle at stops or when changing lines at interchange points. The controller in the process is called the organiser, and the control algorithm is, in the ideal case, using any miss-match between actual demands and available supplies of options (might vary due to disturbances) as the basis for actions which will call upon extra resources or other measures to meet the demands as they appear in realtime. Demand-responsive ation is an example of the realisation of such a function. The two lowest levels are related to the traffic and the motion processes, where the "closedloop s" of drivers and vehicles together constitute the motion process. The traffic process is related not to traffic in general but to the traffic of public vehicles or in other words the flows of vehicles in the network of line routes. The traffic process controller is normally a traffic control centre and its operators and the actuators are the drivers of the vehicles found in the motion. The control actions are control centre commands to be executed by drivers of vehicles in order to - in case of disturbances - bring the traffic back to normal operation according to some criteria - often related to time. A feedback (Info1 in figure 1) is established to provide the operators with actual information about the states of the vehicles (in position and in time). This is sometimes realised as an automatic function called an AVL- or a for automatic vehicle location. General guidelines for how the analytical framework and the conceptual model can be applied for both design and evaluation of public ation solutions have been developed, tested and validated (Franzén 1999a). The model and the framework were successfully applied in the Gothenburg context to help identify design specifications for a group of functions as well as for a study of what effects changes in s design and/or in operations could have on the performance of the total. Such changes in design, and as a consequence changes in performance, are today mainly related to the introduction new functions and services based on advanced information and communication technologies (also known as telematics). 6

7 3 Relations between levels in the model The conceptual model and the analytical framework have also been used to explain the different processes found in public ation as a whole and to further explore the complexity of the total process. Such a development emanates from the high demands on the quality of services for public that are introduced to match user experiences of private means. There will certainly be implications on both humans and organisations from the related introduction of new technologies and some of the issues will be discussed in this section. As the main objective of the total for public ation is to provide travel opportunities and services in the urban area covered, all actors in the must co-operate (if only indirect) towards a common goal. It is, for example, evident that the travel, the, and the traffic processes are highly interrelated and that one cannot exist without the other. For example, a traffic process with no passengers (as part of the ) has no meaning, neither has a process where no vehicles from the traffic are available. The two highest levels of the model are already now basically independent of modes, i.e. the traveller will ideally develop the travel plan with its different links in relation to the purpose of the trip, the time and resource constraints valid at the time of planning and the available options (from time tables etc.). A special need can be identified for the traveller to get access to information about the status of all modes and their respective traffic situation. It should also be mentioned that the knowledge about and the public opinion related to a specific mode that might play an important role in the trip-planning task, this fact being another element in the group of constraints to be applied. In reality the coupling between the levels is more complicated than is indicated here, e.g. with regard to the role of the passenger in the production of services. The conceptual model also clearly indicates the two other perspectives (the individual and the societal) identified in the ation of people. The model and the framework have made it possible to clarify and to develop a better understanding of both the individual perspective of a person seen as a traveller or a passenger, and the societal perspectives of the different actors directly or indirectly involved in the provision of travel and services. However, the perspectives of all types of actors (and their different priorities) need more attention in future development work. It can be expected that the complexity of the total for public ation will increase as the availability of different information sources will increase. Tools, for the collection and the selection of appropriate data or information material to be used in the different tasks at different functional levels, must be developed. For instance, in Gothenburg this would lead to an expansion of the database structure in KomFram, and appropriate filtering functions must be established. By filtering is meant that the amount of data must be reduced in a way which is optimally adapted to the real-time needs of the actors (or actor groups) on each and every functional level. For example, a traffic control centre operator will have the focus on the handling of incidents and disturbances in the traffic. Actions taken will have the aim of bringing traffic 7

8 back to normal conditions again as soon as possible. However, there exist several different and possible chains of actions to resolve an incident and/or disturbance situation. The outcomes of these different action schemes can from the traffic process point of view be almost of equal value, but the consequences for travellers and passengers could be quite different. The question is then how a traffic control centre operator, will be able not directly focused on the travellers and the passengers, to make the best choice of action scheme in order to tackle the traffic incident and its effects on the traffic performance and at the same time minimise the negative effects of the incident on service quality? The answer lies in a support that will make use of aggregated travel and process information to be used in a modified control algorithm. There are also other actors who appear more in the background and could be given support if access to processed (or filtered) information from all functional levels was made available. The most crucial ones are the planners of the and travel services, as they constitute the link between societal and individual needs for movement and the resulting demands to be realised. Today they create the platform on which the services are established and, for instance, an error in a time table could lead to continuous miss-matches between the demands for options as related to travel plan links and the available options. The consequences could be that passengers will miss the planned connections at interchange points, and the following option to be produced would be missing. Such problems can be avoided if different types of support tools are introduced and by such a support the accessibility process would be moved to the left, i.e. the time horizon of accessibility could be decreased to about half a year instead of several years. As a control theoretic approach is central in both the conceptual model and the analytical framework, the local control s introduced on all functional levels are interlinked in a hierarchical structure. 1hr 4 days 0.036s 0.36s 3.6s 36s 360s 3600s 10hrs 100hrs 40 days 1 yr 10yrs motion vehicle dynamics traffic flow control actions time (log scale) (intermodal/integrated solutions) (individual in focus) matching demands travel plan related to activity (society in focus) accessibility resource planning Figure 3 Time horizons of functional levels in the conceptual model (Franzén 1999a) The different time horizons are illustrated in figure 3, where a log scale is used along the time axis to make a comparison possible. 8

9 A slow outer loop can be identified, including political and infrastructure activities and related subs and the next levels are related to the decisions about what options would constitute a preferred movement, and how those demands as well as the matching of existing options with those demands will be dealt with. On the lowest levels are the control centre functions related to traffic operations, and at the bottom, the fastest level is the control of the physical units themselves, i.e. the vehicle platforms. From figure 3 it can be noted that the higher the level the longer the time horizon; however, two of the processes, the and the travel processes, are almost parallel. This fact indicates that a co-ordination of these processes would be rather easy to accomplish, the main difference being that the travel process is mode-independent, while the process is (as the term indicates) mode-related. This fact is also indicated in the model structure as a transformation of the traveller into a passenger when the production of the (mode-dependent) service begins. The complexity of both the total as well as of all the subs involved in public ation is high. There is a high degree of information exchange between different actors, and the nodes for information collection and processing and the links for the necessary information flows between the nodes represent this in the conceptual model. It has been stated (Lumsden et al 1998) that the more complex a ation the more need for information exchange and processing, the cost for the resulting information flows being balanced by a more efficient utilisation of existing and normally limited resources. The closed-loop control process structure of the conceptual model, where the controllers on each functional level can be seen as decision-makers in a complex s structure, also reflects the distributed character of public ation, geographically (or in space) as well as in time. Among others Brehmer (1991) states that if we want distributed decision-making, we need to provide opportunities for communication. Since communication is costly in terms of resources, this may well appear to lead to a that is inefficient. On the other hand, there may be no alternative. If the is complex, some form of distributed control is necessary, and if all problems that the will face cannot be foreseen, communication is needed for the to reconfigure itself. the decision-makers in distributed networks need to be able to reason about their own decision-making activities in relation to those of other decision-makers in the network. Thus, effective distributed decision-making may require a higher level of conscious processing than ordinary individual decision-making. 5 Extensions of the model and the framework The conceptual model and the analytical framework for public ation have been firstly applied in the Gothenburg context, and therefore they are focused on the main two means available, i.e. buses and trams. The type of ation of people studied is also basically that of mass passenger. As a comparison, the situation in reserved seat passenger can be used. In this case the passengers often are given a guarantee that their travel plan links can be realised even if disturbances occur and a option 9

10 is missing. The most obvious cost associated with such a guarantee is that the identity of the passenger normally must be made known to the company. However, other means of passenger can be introduced in an extended framework, i.e. the use of trains, aeroplanes and ships as public means of. In practice this would imply that the motion, traffic and s must be multi-dimensional (one dimension per mode of ). For the moment, and probably within a foreseeable future, every mode will have their own and specific regulatory framework, organisational structure and other mode specific features, the implication being that traffic control operations, training of drivers (pilots, etc.) and organiser functions still would be handled by mode-specific entities in their own right. The private means for the ation of people are also a sector to be added to the conceptual model. This situation is complicated by the fact that the driver of a car is also a traveller (and in principle a passenger) moving from one place to another as part of an activity in business life or as an element of a leisure time activity. As private means also can be seen as a possible way to realise important links in a travel plan, they will play an important role in the context of intermodality. Already today there are examples of measures taken to support such combined use of private and public means, e.g. park and ride schemes. It should also be mentioned that passengers of private cars must be seen as persons which have access to reserved seats and also to relevant information about how to include this specific option in the travel plan. A comparison can also be made with the use of taxis. An important policy issue, presently in focus of European policy-makers, is to identify what measures would accomplish intermodal passenger in the near future. It is possible to use the model and the framework in this context, and firstly, the concepts multimodality and intermodality have to be addressed and defined. Almost every trip is multimodal, i.e. any travel plan includes different modes (including the human legs), but the human being has to make sure that every transition between modes will take place. In reality the person being moved from A to B will, after a transformation from traveller to passenger, make sure that the option chosen for the realisation of the travel plan link is used. The passenger is directly involved in the production of the service itself, both mentally and physically. In an intermodal case, the traveller at the most has to choose between different options for the journey between A and B when planning the trip, and someone else (the organiser node in figure 1) will take care of any disturbance that might occur in the. In an intermodal the traveller is given a guarantee that the destination will be reached as planned, and that any problem in the process that might occur will be solved without any burden on the passenger. What is clearly stated here is that intermodal (or seamless travel) requires that the process is modified to include both a feedback loop (Info 2) and a controller (the organiser) with access to relevant and timely control actions and actuator outputs. In the EC project HINT (Franzén 1999) this realisation problem has partly been addressed using an argumentation based on figure 4. The model and the framework have been applied in order to identify where in the total the efforts toward intermodality (or rather the integration of functions from different modes) should be put. The modes are characterised 10

11 using the two dimensions of passenger control of situation (full to none) vs. type of journey (long infrequent to short and frequent) is used (Franzén 1999b). Self operated Operated by someone-else Level of Control Full None Type of journey Short and frequent Pedestrian Car Individual, Personal Transport Taxi Bus Coach Public Transport Rail Long and infrequent Air Figure 4 The difference between modes along two axes, level of control and type of journey (Franzén 1999b) The potential for integration between modes depends on the position and overlap of the modes in the diagram in figure 4. From the diagram can be concluded that if several modes "overlap", they are in competition, but information services for travellers and passengers must be provided if quality should be maintained. If one mode is more dominating, the competition can be seen between different option providers and traffic operators, and appropriate and efficient terminal arrangements (including "feeder" modes) are important for high quality of the services offered. In this context it is also necessary (and useful) to make a comparison between reservedseat passenger and mass passenger. In the first case, the traveller or a travel agency will reserve seats, and a guarantee is issued (even if it is not clearly outspoken) that alternative options will be made available if the reservations do not work properly. However, in mass passenger, the risk of reaching an undercapacity situation, i.e. a place (seat) in the vehicle, which is decided to be the matching 11

12 option, is not available, has brought (or rather forced ) the process closer to the characteristics of the traffic process. In a recent document form the European Commission (1998) a step-by-step action list towards this ideal situation is presented. It is stated that in several areas an integrated approach towards intermodality should be chosen. In practice this means that the starting point should be the identification and the integration of already existing (but mode specific) s such as ticketing and payment s, access to time tables and other similar information material, and the provision of real-time traveller and passengers information services covering most of the modes available in an area As a preliminary conclusion from the evaluation of intermodal services from a passenger's perspective (cp. Franzén 1999b, Carsten et al 1999), it can be stated that there has been identified a need to promote the societal perspective in public ation. As the basic technologies for intermodal solutions already exist, some fundamental questions for the development of intermodality are raised: Who will take the responsibility for the implementation of intermodal service?, Can and will society pay for all the necessary infrastructure?, and finally Is there a business case to be found in intermodality for ation of people?. 6. A holistic view on ation of people As a conclusion of the work and reasoning presented here it can be stated that the model and the framework will contribute to the better understanding of all types of ation of people. The s perspective applied indicates that every actor (e.g. drivers, control operators, passengers, travellers, politicians, etc.) found in this complex human-machine must be understood and studied not in isolation and inside one single process level itself, but must be seen as and integrated part of a whole and related dynamically to all other functional levels of the ation. It is important to state that such a holistic view on ation of people is necessary in order to accomplish a development process aiming for the ation of the future. No can perform better than what the weakest link or element of the can allow. The conceptual model and the analytical framework are therefore necessary tools for the establishment of more in-depth knowledge of what new functions and services should be introduced in the context of ation of people. This will be especially important in an urban environment, where future solutions must be sustainable and incorporate all types of means, both private and public. 7 References Brehmer, B. (1991): Distributed Decision Making: Some Notes on the Literature, in Rasmussen, J., B. Brehmer, J. Leplat (Eds.) (1991): Distributed Decision Making - Cognitive Models for Co-operative Work, John Wiley & Sons, New York. 12

13 Carsten, O., S. Franzén, M. Draskóczy, E. Carver (1999): Monitoring and Control of Human Implications of New Technology, Deliverable 11, CEC project HINT (Contract No ST-96-AM-1024), European Commission, Brussels. CEC (1996): The Citizens Network. Fulfilling the potential of public passenger in Europe, European Commission Green Paper, Brussels. EuroCASE (1996): Mobility, Transport and Traffic in the perspective of Growth, Competitiveness, Employment, CEC DG XII Project Report, EuroCASE. European Commission (1998): Developing the Citizens Network. Why good local and regional passenger is important, and how the European commission is helping to bring it about, COM(1998) 431 final, Communication form the Commission, Brussels. Franzén, S. (1999a): Public Transportation from a Systems Perspective. A conceptual model and analytical framework for design and evaluation, Report 40, Dept of Transportation and Logistics, Chalmers University of Technology. Franzén, S. (Ed.) (1999b): Transport Services and Intermodality: human implications of new technology, Deliverable 8, CEC project HINT (ST-96-AM-1024). Franzén, S., M.A. Karlsson, H-Å Pettersson, L. Wikström (1994): "A User-Oriented Systems Approach to Public Transport Passenger Information Services", Proc. 1 st ITS World Congress, Paris, Nov Dec 3. GoTiC Research ( ): GoTiC Research Reports (no. 1-10), and GoTiC News, Gothenburg Traffic and Public Transport Authority, Gothenburg. Lumsden, K., L. Hultén, J. Waidringer (1998): Outline for a Conceptual Framework on Complexity in Logistics Systems, in Proceedings of NOFOMA '98, June 1998, Helsinki. Manheim, M. (1979): Fundamentals of Transportation Systems Analysis - Volume 1: Basic Concepts, MIT Press, Cambridge. OECD (1996): Integrated advanced logistics for freight, OECD, Paris. Rasmussen, J., A.M. Pejtersen, L.P. Goodstein (1994): Cognitive Systems Engineering, John Wiley & Sons, New York. Sjöstedt, L. (1994): Sustainable Mobility - A Systems Approach in Policy Issues addressed by the 10 th CAETS Convocation in Zurich, Report (Meddelande) 75, Dept of Transportation and Logistics, Chalmers University of Technology 13