Lecture 2. Transportation Process Technology and the Supply Chain

Lecture Outline

1. Transportation Systems and Systems Analysis.

2. Classification of Systems.

3. Production and Transport Systems.

4.Transportation System Identification and Research

2.1TransportationSystems and Systems Analysis

Process refers to a repeated, follow-up, unbreakable change of development moments (for instance, process of car assembly).

Transportation process is defined as production process of moving goods (freight) from the place of production to places of consuming.

System is an objective unity of interrelated components, concepts, notions, and knowledge of nature and society.

A transportation system can be defined as a set of elements and the interactionsbetween them that produce both the demand for travel within a given area and theprovision of transportation services to satisfy this demand. Almost all of the components of a social and economic system in a given geographical area interact atsome level of intensity. However, in practice it is impossible to take into accountevery interacting element when addressing a given transportation engineering problem. The general approach of systems engineering is to isolate the elements mostrelevant to a problem at hand, and to group these elements and the relationships between them within the analysis system. The remaining elements are assigned to theexternal environment; they are taken into account only in terms of their interactionswith the analysis system. In general, the analysis system includes the elements andinteractions that an action under consideration may significantly affect. Hence thereis a strong interdependence between the identification of the analysis system andthe problem to be solved. The transportation system of a given area can also be seenas a subsystem of a wider territorial system with which it strongly interacts. The details of the specific problem determine the extent to which these interactions areincluded either in the analysis system or the external environment.

These concepts can be clarified by some examples. Consider an urban area consisting of a set of households, workplaces, services, transportation facilities, government organizations, regulations, and so on. This system has a hierarchical structureand, within it, several subsystems can be identified (see Fig. 1.1). [ p.19, Transportation Systems Analysis ].

One of the subsystems – the activity system – represents the set of individual, social, and economic behaviors and interactions that give rise to travel demand. Todescribe the geographic distribution of activity system features, the urban area istypically subdivided into geographic units called zones. The activity system can befurther broken down into three subsystems consisting of:

• The households living in each zone, categorized by factors such as income level,life-cycle, composition, and the like

• The economic activities located in each zone, categorized by a variety of socioeconomic indicators (e.g., sector of activity; value added; number of employees)

• The real estate system, characterized by the floor space available in each zone forvarious uses (industrial production, offices, building areas, etc.) and the associatedmarket prices.

The different components of the activity system interact in many ways. For example, the number and types of households living in the various zones depend inpart on employment opportunities and their distribution, and therefore on the economic activity subsystem. Furthermore, the location of some types of economicactivities (retail, social services such as education and welfare, etc.) depends on thegeographic distribution of the households. Finally, the number of households and theintensity of economic activities in each zone depend on the availability of specifictypes of floor space (houses, shops, etc.) and on their relative prices. Detailed analysis of the mechanisms underlying each subsystem of the activity system lies beyondthe scope of this book. However, it should be noted that the relative accessibility ofthe different zones is extremely relevant to many of these mechanisms.

Another subsystem – the transportation system – consists of two main components: demand and supply.

Travel demand derives from the need to access urban functions and services indifferent places and is determined by the distribution of households and activities inthe area. Household members make long-term “mobility choices” (holding a drivinglicense, owning a car, etc.) and short-term “travel choices” (trip frequency, time,destination, mode, path,1 etc.), and use the transportation network and services sothat they can undertake different activities (work, study, shopping, etc.) in differentlocations. These choices result in travel demand flows, that is, the trips made bypeople between the different zones of the city, for different purposes, in differentperiods of the day, by means of the different available transportation modes. Similarly, economic activities require the transportation of goods that are consumed byother activities or by households. Goods are moved between production plants, retail locations, and houses or other “final consumption” sites. Their movements makeup freight travel demand and corresponding flows.

Both mobility and travel choices are influenced by the characteristics of the transportation services offered by the available travel modes (such as private vehicles,transit, walking). These characteristics are known as level of service or performanceattributes; they include travel times, monetary costs, service reliability, riding comfort, and the like. For instance, the choice of destination may be influenced by thetravel time and cost needed to reach each alternative destination; the choice of departure time depends on the travel time to the destination and the desired arrival time;and the choice of transportation mode is influenced by the time, cost and reliabilityof the available modes.

*The term path is used in the book to define both a choice alternative and a path in a graph. The term route is also used in the literature with either or both of these meanings.

The transportation supply component is made up of the facilities (roads, parkingspaces, railway lines, etc.), services (transit lines and timetables), regulations (roadcirculation and parking regulations), and prices (transit fares, parking prices, roadtolls, etc.) that produce travel opportunities. Travel from one location to anotherfrequently involves the successive use of several connected facilities or services.

Transportation facilities generally have a finite capacity, that is, a maximum numberof units that may use them in a given time interval. Transportation facilities alsogenerally exhibit congestion; that is, the number of their users in a time unit affectstheir performance. When the flow approaches the capacity of a given facility (e.g., aroad section), interactions among users significantly increase and congestion effectscan become important. Congestion on a facility can significantly affect the levelof service received by its users; for example, travel time, service delay, and fuelconsumption all increase with the level of congestion.

Finally, the performance of the transportation system influences the relative accessibility of different zones of the urban area by determining, for each zone, thegeneralized cost (disutility) of reaching other zones (active accessibility), or of being reached from other zones (passive accessibility). As has been noted, both thesetypes of accessibilities influence the location of households and economic activities and ultimately the real estate market. For example, in choosing their residencezone, households take account of active accessibility to the workplace and other services (commerce, education, etc.). Similarly, economic activities are located to takeinto account passive accessibility on behalf of their potential clients; public servicesshould be located to allow for passive accessibility by their users, and so on.

Several feedback cycles can be identified in an urban transportation system.

These are cycles of interdependence between the various elements and subsystems. The innermost cycle, the one that involves the least number ofelements and that usually shows the shortest reaction time to perturbations, is the interaction between facility flows, the performance due to congestion and transportation costs, in particular those connected with road transportation. The trips made bya given mode (e.g., car) choose from among the available paths and use traffic elements of the transportation network (e.g., road sections). Due to congestion, theseflows affect the level of service on the different paths and so, in turn, influence userpath choices.

There are also outer cycles, cycles that influence multiple choice dimensionsand that involve changes occurring over longer time periods. These cycles affectthe split of trips among the alternative modes and the distribution of these tripsamong the possible destinations. Finally, there are cycles spanning even longer timespans, in which interactions between activity location choices and travel demand areimportant. Again, through congestion, travel demand influences accessibility of thedifferent areas of the city and hence the location choices of households and firms.

It is clear from the above that a transportation system is a complex system, thatis, a system made up of multiple elements with nonlinear interactions and multiplefeedback cycles. Furthermore, the inherent unpredictability of many features of thesystem, such as the time needed to traverse a road section or the particular choicemade by a user, may require the system state to be represented by random variables.

As a first approximation, these random variables are often represented by their expected values.

Transportation systems engineering has traditionally focused on modeling andanalysis of the elements and relationships that make up the transportation system,considering the activity system as exogenously given. More specifically, it has typically considered the influence of the activity system on the transportation system (inparticular on travel demand), whereas the inverse influence of accessibility on activity location and level has usually been neglected. However, this divide is rapidly vanishing and transportation system analysis increasingly studies the whole activity–transportation system, albeit at different levels of detail than do disciplines such asregional science and spatial economics.

The aim of transportation systems engineering, as shown in greater detail be low, is to design transportation systems using quantitative methods such as thosedescribed in the following chapters. Transportation projects may have very differentscales and impacts, and consequently the boundaries between the analysis systemand the external environment may vary considerably.

If the problem at hand is long-term planning of the whole urban transportationsystem, including the construction of new motorways, railway lines, parking facilities, and the like, the analysis has to include the entire multimode transportationsystem and possibly its relationships with the urban activity system. Indeed, theresulting modifications in the transportation network and service performance characteristics and the time needed to implement the plan are such that all componentsof the transportation and activity systems will likely be affected.

There are cases, however, in which the problem is more limited. If, for example, the aim is to design the service characteristics of an urban transit system without building new facilities (and without implementing new policies affecting othermodes, such as car use restrictions), it is common practice to include in the analysissystem only those elements (demand, services, prices, vehicles, etc.) related to public transportation. The rest of the transportation system is included in the externalenvironment interacting with the public transportation system.

As shown, the above examples can be generalized toareas of different size (a region, a whole country, etc.) and extended to cover freighttransportation.

2.2. Classification of Systems

The objective reality shows an example of united material system. During research, it is subdivided into local systems: biological, social, economic, ecological, physical, chemical, etc. The above-mentioned systems are grouped into:

· abstract and concrete,

· natural and artificial,

· social, machine and “man-machine” systems,

· open and closed systems,

· permanent and temporary,

· stable and unstable,

· determined and probable.

Abstract and concrete systems. The system is called abstract if its elements are abstract notions. Abstract systems are connected with theoretical structures and are composed of ideas, for instance, economic theory, theory of probability, etc.

Concrete (real) systems are functionally related elements (men, machines, materials, energy resources and other physical objects). In transport industry, concrete systems are: system of freight transport, system of public passenger transport, spatially limited transport systems, etc.

Natural and artificial systems. Natural systems are connected with nature. Every living body is a unique natural system (for example, solar system).

Artificial systems emerged when people gathered in groups to hunt and live together for the first time. Now, artificial systems constantly emerge in many variants, from production systems of a road transport enterprise to a space exploration system.

Social, machine and “man-machine” systems. Systems composed of people are referred to as purely social. Industrial, transport and other enterprises, political parties, technical societies serve examples of social systems. However, it is hard to imagine any system of people who do not use at least the simplest equipment. Therefore, most concrete systems belong to the subgroup of “man-machine” systems.

Purely machine systems are supposed to produce their output data and maintain their functioning, i.e. to be capable of adjusting to the environment.

Open and closed systems. Opensystemsareclosely related with other systems which influence each other. In other words, open systems are interacting with the environment.

Systems containing live organisms as their components are referred to as open. Transport systems function within bigger systems and thus, are open systems.

In open systems, the same state can be reached at various initial data due to interaction with the environment. Opensystemsaredividedintoadaptableandnon-adaptable.

Closed systems do not interact with the environment. The state of closed systems depends on their initial data. If the data changes, the final balanced state of the system will shift as well. Any try to regard open systems as closed systems, when the environment is not taken into consideration, may be very dangerous.

In reality, closed systems are hard to find. There are numerous applications of closed systems in research and laboratory experiments to simplify analysis of some production situations.

Permanent and temporary systems. Permanent systems denote systems existing for a long period of time in comparison with the limited time of human activity within those systems.

Temporary systems have great importance in specified problem solving and are created for a given time period to be terminated later (e.g. vehicle caravans for transportation of harvested wheat).

Stableandunstablesystems. A system is considered to be stable,if its parameters and functions do not significantly change or the changes take the form of repeated cycles (e.g. the system of regular international freight or passenger transportation). A research and development laboratory serves an example of an unstable system.

Determined and probable systems. A determined system defines a system where the components interact in an exactly forecast mode (e.g. a sewing machine). If the previous output data and operation program of the determined system is known, the future status of the given system is easy to predict.

Computers, automated systems and automated enterprises are determined systems. Any deviation from the prescribed mode of operation is considered to be a malfunction or an accident.

Probable systems are difficult to predict. It is possible to forecast with due probability how the system reacts for the given parameters. Transportation systems are referred to as probable systems. They require methods of management which maintain survival and functioning of the system in the conditions of the changing environment. Probable systems need to adjust to the given economic, financial, social and political environment. Such systems are supposed to learn from the previous experience.

Subsystems and Suprasystems in Transport

Any system is included into a bigger system. Thus, a road transport enterprise is a part of an industry. The given industry is an element of the national economy which serves a part of the entire society. The national society becomes a component of the global community, whereas the global system is included into the solar system, etc.

Transportation enterprise is regarded as a system only if the focus in analysis is on transportation of freight or passengers, and if the enterprise is composed of all objects, features and relations required for achieving the given goal at a defined number of limitations. Smaller systems within such system are called subsystems.

The term suprasystem is applied exclusively to large and complicated systems. Asystem needs to meet the requirements of the bigger systems where it is included.

2.3. Production and Transportation Systems

The degree of complexity of freight transportation process can vary greatly (for instance, transportation of individual packed freight between countries). Many procedures are performed during freight transportation.

Production (transportation) processes

A production process refers to a set of different man and machine labour operations performed in a given order and interrelation to accomplish a given production task. In transport, production process stands for moving freight from place of production to place of its consumption.

Operationis part of production process carried out by employees in their workplace (fixed or movable).

Notwithstanding its type, technological process of transportation can be successfully performed on condition that a production management system is functioning. The system of management of production processes at the input and output point is represented on the diagram below.

Transportation system in its primary approximation can be regarded as a group of mechanisms (vehicles, loaders, etc.) that are operated by operational personnel (drivers, crane operators, etc.). Every mechanism and its operator form the “man-machine” system out of two interacting and interrelated units. Following the process of integration, we face a more complicated system, a transport complex. Transport complex includes main and supporting staff of employees, main and supporting equipment, and is specified by a number of relations, interests, and has a complicated structure.

In fact, any system is a whole of interacting components, each representing a single system which includes another set of elements. Systems are distinguished by their objectives (loading and unloading operations, moving freight, etc.)

Systems approach enables unification of the disintegrated transportation process and reaching order in the process. The components of a system are characterized by a number of properties. The propertiesofcomponentsimpactfunctioningofthesystem, its action, reliability, capacity, etc. In creating transportation systems, the choice between man and machine systems, various types of movable fleet, loading and unloading vehicles and relevant personnel based on the features of transportation systems is under consideration.

Transportation system (transport complex) refers to the partially self-controlled system with the following properties:

· type of the system is “man-machine”;

· the system is able to choose the type of its activity; responsibility can be distributed between the components of the system based on their functions (freight handling before transportation, loading, transportation proper, etc.);

· objectives and relevant activity need to be distributed between the components of the system.

For achieving the goals set in freight transportation management, both good and bad transportation systems can be created. For example, transportation complex for harvesting and transportation of the harvest may be an inefficient system in case of long downtime of the trucks when the combineharvestersare not available and vice versa. A transportation system can be considered efficient if the given set of variables related to its functioning remains within the given limits all the time.

2.4. Transportation System Identification and Research

Transportation system identification is the definition of the elements and relationships that make up the system to be analyzed. It includes the following steps:

• identification of relevant spatial dimensions;

• identification of relevant temporal dimensions;

• definition of relevant components of travel demand.

Some comments on the different steps are given below. However, it should bestated at the outset that system identification cannot be reduced to the mere application of a set of rigid rules. Rather, it requires the application of professionalexpertise, which is acquired by combining experience with a thorough knowledgeof the methods of transportation systems engineering.

Systems approach is applied in:

· design of new processes and systems;

· reforming of a given system, comparison and assessment of the advantages of different plans;

· consideration of interrelations between a given individual task and external conditions; identification of factors and variables that influence the situation under the given conditions;

· design of a scheme for evaluation of various subsystems and the system on the whole;

· identification of disorder and misconception of objectives relating to individual executors in functioning of a single system.

The general notions of systems analysis applied to transport objects allow formulation of a fixed order of research and decision-making in transportation.

The stages of transportation systems research are suggested below.

Stage 1. Identification of objectives and functioning of the subject of research, defining the criterion of system’s efficiency.

Stage 2. Definingthebordersofthesystem.

Stage 3. Identification of the structure of environment.

Stage 4. Research of the structure of transportation system; identification of its elements.

Stage 5. Investigation of the characteristic interrelations between the elements of the system; design of the mathematic model of the system’s behaviour.

Stage 6. Search of the optimum state for the devised mathematic model of transportation system.

Stage 7. Development of management directions aimed at achieving the optimum state of the system.

Поиск по сайту: