- Email: [email protected]
Road Trains of Heavy Trucks as Highway Commercial Transportation Systems
Copyright © IFAC Large Scale Systems. Rio Patras. Greece. 1998
ROAD TRAINS OF REA VY TRUCKS AS RIGHW AY COMMERCIAL TRANSPORT ATION SYSTEMS
S. A. Manesis
Electrical and Computer Engineering Dept. Division of Systems and Control University of Patras [email protected]
Abstract: Today more than ever efforts of governments and companies try to provide safe and efficient transportation through air, over water and on land. Current highway transportation systems, except of the intelligent and automated aspect, do not present any other significant development especially concerning the "truck vehicle". This paper proposes the idea of long truck-trains with multiple semi-trailers as highway vehicle systems for freight transportation. The basic mechanical characteristics of the truck-train are described and the corresponding steering problems are introduced. The paper states also the path following problem and includes a discussion of the various traffic and steering rules that must be applied when a truck-train travels on a multi-lane highway. Copyright © 19981FAC
Keywords: Transportation systems, heavy trucks, vehicle trains.
1.
INTRODUCTION
al. (1994). Many other similar issues on the same topic (AHS) is the object of research (Horowitz, 1997; Mammar, 1997; Broucke and Varaiya, 1997; Alvarez, et ai., 1997; Hessburg and Tomizuka, 1994; Passino, 1995). In a classic example of developing new applications for remote sensing, the European Microwave Signature Laboratory is helping DaimlerBenz improve driver safety. The Institute for Remote Sensing Applications launched the ROCOCO (ROad COndition and COntrol) project in June 1995 with Daimler-Benz in order-as the partners hope-to reduce one day the traffic accidents (- a, 1995).
During the last decades transportation of people and goods has heavily increased. More demands than ever are recorded on airports, shipping lines, highways and railways. This situation as also the future requirements have led companies and governments to fmance several projects in order to improve their air and land transportation technology. A review paper (Dooling, 1996) provides an overview of today's directions in transportation technology. Modem air traffic control, safety against microbursts, terrific trains, smart ships, intelligent highway and global positioning system (GPS) are some of the keywords that express the innovative concepts in transportation.
Developed by European broadcasters and car radio manufacturers since the mid-1980s, Radio Data Systems (RDS) will play a major role in making road transport more efficient. Bosch and Philips companies began working on Traffic Message Channel (RDS-TMC) technology which enables thousands of coded traffic messages to be broadcast via RDS code (- b, 1996). In this way, RDS-TMC data providing updates on traffic, weather and more, road transport will flow even smoother. In USA on the other hand, in order to put highway traffic on a par with air traffic, a master plan for an Intelligent
In road transportation, the automated highway systems, the microprocessor-based vehicle controls, the road radars, the advanced GPS and the radio technologies are being applied - at research level until now - in all forms of passenger and freight transportation. The basic vehicle control issues that must be faced in designing a fully automated highway system (AHS) are described by Hedrick, et 361
Transportation System (ITS) was drawn by the corresponding US department. To San Antonio, Texas opened the country' s first municipal ITS while Colorado state dispose a smart highway exit (Interstate 70-Denver) which has a 9-Km downgrade where many runway trucks there have been over the last years. Sensors embedded in the roadway will enable computers to monitor truck speed and weight and to flash messages on roadside signs to warn drivers to slow down (Dooling, 1996).
TEN). In parallel, another RTD programme in the field of transport began in December 1994 which had a total budget of 240 Mecu and covered seven areas one of which was the road transport (- d, 1994). Although we note the above global effort for improvement of road transport conditions, in the field of freight transportation especially we have not a radical change of the predominant situation. We can say that it is characterized by the phrase "we see excellent highways full with excellent truck vehicles, so full that is dangerous to drive our car". As it is explained in the following chapters, the road freight transportation seems to have disadvantages against ship and railway transport. The paper proposes the introduction of "road trains" in the highway systems and international autobahns. The road trains will consist of a number of trailers (approximately 10-20) and a lead tractor. In order such a road train of trucks to be steerable with safety in a multi-lane highway a set of traffic rules must be defmed, the pathfollowing problem must be solved, the mechanical realization must be examined and the space limitations outside a highway must be taken care of. These aspects are some of the basic ones that are addressed in this paper.
A number of European projects concerning the transport policy have been elaborated during the last decade. In the 1980s vehicle manufacturers began to realize the limitations imposed by the increasing volume of vehicles in the European transport network. These limitations were due to urban congestion, increased cost from time devoted to travelling, accidents, safety, security, environmental pollution and the need to utilize the time spent on driving more efficiently. Subsequently, manufacturers envisioned the possibility of a new transport system based on the application and of electronics, computers and integration telecommunications to reduce these limitations. This gave birth to a research programme entitled PROMETHEUS (began in I986) consisting of three subprogrammes PRO-CAR, PRO-ROAD and PRONET. Later, it was established as an European Union backed EUREKA project (EU-45) investigating improvements in safety and efficiency on the roads. For a summary of PROMETHEUS' s aims as also of a parallel programme entitled DRIVE see (Nwagboso, I997).
2.
THE ROAD TRUCK TRAIN
The road freight transportation is performed today by several (more than 20) types of trucks as also by combinations of trucks, tractors and trailers. The longest of them are used in the case of international freight transportation between different countries. The four longest vehicle combinations are shown in Fig.1 and are coded as Tx-STy-Tz- .. . that means Tractor and Semi-Trailer and Trailer (stand alone) and ... , each with x,y,z, .. . axles correspondingly. There are also several types of rigid lead vehicles (RV) combined with trailers. All the above complex vehicles are usually driven by one or two drivers . In comparison with the other modes of freight transportation, ship and railway, truck vehicles seem to have an inherent disadvantage that is the small coefficient of useful weight per driver or in general per worker. For example, a medium size commercial
The European Commission's White Paper on "The Future Development of the Common Transport Policy" (CTP) was the first step towards defming goals of CTP and establishing the work programme to achieve them ( - c, I995). The ratification of the Treaty of Maastricht marked the beginning of a new phase for developing further the CTP. Also, it underlined the importance of the basic goals such as improvement in safety, sustainable growth respecting the environment integration of transport systems via intermodality and the quality and effectiveness of transport infrastructure (Trans-European Network-
T3-ST2-T2
T3-STl-T2-T2
T3-ST3
RV3-T3 Fig. l . The longest truck-trailer vehicles. 362
ship may transfer one hundred containers with only fifteen persons as crew. For road transportation of these containers, we need fifty RV3-T3 vehicles approximately, which require an equal number of drivers. The comparison is much more negative for truck vehicles if the ship is a large one. Similarly, a train with twenty railroad cars usually requires only two or three drivers .
[[:
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IEI
method. The main advantages of using truck trains in highway freight transportation are the following: a) The aggregation of the multiple autonomous trucks in fewer (let more complex) truck trains. b) From the accident point of view, ten autonomous trucks in a high density autobahn are much more dangerous than a truck train with ten trailers.
IEI
IEI
IEI
II
Fig.2. The road truck train. During the last years, traffic in international autobahns has heavily increased following that in population centres. In order to face the difficulties of the high traffic density, several methods have been developed to increase safety and to optimize the throughput of highways. Various techniques on various topics concerning all kinds of car have this goal, as e.g. anti-lock brakes, AHS, collision avoidance strategies, sensor based driving, antiskidding robust control etc. (Horowitz, 1997; Mayr, 1997; Gissinger and Kortun, 1997; Bielli et al., 1997; Ackermann, 1997). Large truck vehicles occupy a significant percentage of the total traffic while they are increased day by day. In spite of the existent high-capacity autobahns, large truck vehicles it is expected to fill moreover them. Furthermore, they can achieve high speeds even with full load, and hence may cause accidents Gackknifmg leads out of control) especially under rainy and misty conditions.
c) The velocity of a truck train may be less than that of an autonomous truck but the fmal benefit will be of the truck train because of the multiple transported load. d) It is obvious that the vehicle emissions, noise and visual intrusion will be reduced. e) Major flexibility of the freight transportation system because of the interchangeability of the semi-trailers in the intermodal stations. f) Improvement of the safety because of the lower mean speed and of the stricter procedure for a lane change. The above concept of road truck trains imposes a series of problems concerning traffic, steering and control that will be introduced briefly in the following chapters.
A key to improving capacity and safety in an autobahn is the "hard platooning" of long truck vehicles that is a truck train. Soft platooning is the organization of groups of tightly spaced cars in an automated highway system. The truck traffic density in a highway is such that many platoons of truck vehicles are usually formed, especially in highways with few lanes. The simple dilemma is why these platoons of truck vehicles could not be a truck train in the form of a multi-trailer system. We can defme a truck train as the T5-nSn tractor/semi-trailer combination that is a high power tractor with five or more axles, which pulls n passive semi-trailers as shown in Fig.2. The number n may be assumed between 6 and 10 at first stage of development. We assume that the tractor has the required power to pull the semi-trailers and also that exist all the technical presuppositions which secure a smooth movement on the road. Another basic characteristic is that the kingpin hitch of each semi-trailer is on the center of the back pair of axles. This assumption is important for the application of an off-trucking elimination
The motion of a truck train in a multi-lane highway introduces a number of traffic problems. These are described in detail (Manesis, 1997). In this chapter, attention is focused only on the most significant of them. First of all, it must be clear that the truck trains are destined for movement only on multi-lane (;:: 3 in each direction) highways. When a truck train travels on a multi-lane highway problems arise due to the presence of other cars and needs for lane changes. As shown in Fig.3a, a crash may happen between the truck train and the private car since the car enters on the free side area of the train while it is changing lane. In this case, the known rule for left or write turn after a flash signal is not valid and a new one must be defmed. Another problem is that the driver of the long truck train can not estimate exactly, via his mirror, the distance of the side car and hence if it is inside the "effective area" of the train. In this case, a sensor based rule for a turn maneuver must been defmed. Fig.3b shows also that the classical overtaking is not permitted since the truck train encages the small car.
3. TRAFFIC RULES
363
It'
[: :1
It'
It'
It
-------------------------------------------------
(a)
(b) Fig.3. Examples of truck train traffic problems. the lead tractor during a turn at low speed. As in the case of a tractor pulling one semi-trailer, the offtracking is quantifIed successively for the last semitrailer in a convoy consisting of a tractor with more than five or ten semi-trailers. A closed-form expression for the off-tracking of the rear pivot point of a simple T3-STl vehicle can be found in (Alexander and Maddocks, 1988) while off-tracking bounds for a car pulling trailers have been derived in (Bushnell et al., 1994).
As already mentioned, the truck trains are destined to travel in autobahns between large towns and never inside them. In the peripheral zone of each town there will be a parking area adjacent to the autobahn where the truck trains will be composed/decomposed from/to individual semitrailers. These will be taken by independent local tractors in order to be transferred in the town, port or elsewhere. In the form of a container parking area, the truck train one will be a two-modal transportation station where simple semi-trailers will compose train vehicles and vice-versa. Consequently, every truck train is engaged in one of a fmite number of actions such as entering the highway, changing a lane, exiting the highway, temporary parking in a layby etc. The "travel" of the track train in a highway can be summarized by the sequence of actions that the complex vehicle executes. All the above problems can be faced and hence the "travel" of the truck train can be safe and effective, if we defme traffic rules with concrete priorities against other cars and actions in each case of traffic activity.
In the case of the proposed truck train, it is
imperative than any other case, e.g. classical trucktrailer vehicles, car-like multibody mobile robot and luggage carrier in an airport, that the last semi-trailer follows exactly the path of the lead tractor during a turn for lane change or a turn due to the curvature of the highway. Otherwise, it will be possible the last semi-trailer to violate the outer boundary of the highway or to crash with an adjacent car during a lane change although both keep invariant their relative velocity. The off-tracking problem has been studied by several authors; among the fIrst were Ervin and Guy, (1986). The case of equal length kingpin hitches (the kingpin between the bodies of the vehicles) has been simulated by Bushnell et al., (1994) but can not be applied to heavy duty trucks and trailers. On the other hand, steerable trailers are of increasing interest because they can make turns around corners more manageable but have been studied mainly for the case of one rear axle equipped with steerable wheels and for one trailer. A multisteering and multitrailer
4. THE OFF-TRACKING PROBLEM
The steering of a long truck train on a multi-lane highway will be a major problem in terms of public safety and traffic smoothness. Among the various truck train maneuverability and stability problems, the most basic will be the so-called off-tracking one and is the fIrst that we must face. Off-tracking is defmed as the deviation of the semi-trailers' axles or the kingpin hitch from the path of the steering axle of 364
system has been studied by Tilbury et al., (1995) from the kinematic model point of view, which can not be applied in the case of a truck train. Furthennore, if a steerable trailer technique is going to be applied in a heavy trailer with two or three rear axles then it seems that it will be an expensive solution.
Dooling D., (1996) "Transportation", IEEE SPECTRUM, January pp.82-86. Ervin R.D. and Y.Guy, (1986) "Axioms relating size and weight constraints to the response of trailers in combination trucks", Int. Symp. on Heavy Vehicle Weights and Dimensions, Ottawa Canada. Gissinger G.L. and W. Kortun, (1997) " Simulation of Vehicle System Dynamics, State of the Art and Ongoing Developments", Proceedings of the gh IFAC Sy mp. On Transportation Systems, Chania Greece. Hedrick J.K. , M. Tomizuka and P. Varaiya, (1994) " Control Issues in Automated Highway Systems", IEEE Control Systems, pp.21-32. Hessburg T. and M. Tomizuka, (1994) "Fuzzy Logic Control for Lateral Vehicle Guidance", IEEE Control Systems, pp.55-63. Horowitz R., (1997) "Automated Highway Systems: The Smart Way to Go", Proceedings of the gh IFAC Symp. On Transportation Systems, Chania Greece. Mammar S., (1997) "Robust Automatic Steering of a Vehicle: an LMI approach", Proceedings of the
The off-tracking is eliminated by sliding each trailer with respect to the previous, a technique described in (Manesis, 1998). According to this, the kingpin hitch in each semi-trailer slides in a direction perpendicular to the longitudinal axle of the trailer. The sliding width varies as a linear or exponential function of the front wheel turning angle. A basic assumption of the method in order to be applicable is that the lead tractor doesn ' t perfonn sharp turns. In the case of the truck train, this is satisfied because the radius of curvatures of the highways is not pennitted to be less than 700 m. Then, as it is pointed out the required sliding width doesn't exceed 25 cm. By eliminating the off-tracking, the driver of the truck train doesn' t need anymore to turn far to the desired path because of the path deviation of the rear trailers.
8'h IFAC Symp. On Transportation Systems, Chania Greece. Manesis S., (1997) "On highway trafficability and followability of extra long trucks with multiple semi-trailers", Technical report, Systems and Control Division, University of Patras, Greece. Manesis S., (1998) "Off-tracking elimination in road trains of heavy duty trucks with mUltiple semitrailers", Proceedings of the gh IFAC Symp. On Large Scale Systems: Theory and Applications LSS'98, Patras Greece. Mayr R. , (1997) "Driving Comfort in Sensor Based Lateral Vehicle Control", Proceedings of the gh IFAC Symp. On Transportation Systems, Chania Greece. Nwagboso c., (1997) "Advanced Vehicle and Infrastructure Systems: Computer Application, Control and Automation", 1. Wiley & Sons. Passino K.M., (1995) "Intelligent Control for Autonomous Systems", IEEE SPECTRUM, pp.55-62. Tilbury D., 0.1. Sordalen, L. Bushnell and S. Shankar, (1995) "A Muitisteering Trailer System: Conversion into Chained Fonn Using Dynamic Feedback", IEEE Trans. on Robotics and Automation, pp.807-817, voUI, No.6. -a, (1995) "IRSA: Radar on the road", Innovation and Technology Transfer, pp.l9, vol.5 . ~, (1996) "Wiring the Roads" , Innovation Technology Transfer, pp. 13, vol.2 . --c, (1995) "The Common Transport Policy Agenda 1995-2000: An action programme towards sustainable mobility in Europe", European
5. CONCLUSIONS Ground transport, both public and private, will continue to develop to meet perceived social and economic needs; technological changes are undoubtedly expected. In this paper the concept of truck trains as highway transportation systems is proposed. The basic aspects and problems arising from such a technical challenge have been presented.
REFERENCES Ackennann J., (1997) "Robust Control Prevents Car Skidding" , IEEE Control Systems, pp.23-31. Alexander J.C. and J.H. Maddocks, (1988) "On the Maneuvering of Vehicles", SIAM Journal Applied Mathematics, pp.38-51 , vol.48, No.l. Alvarez L., R. Horowitz and P. Li, (1997) "Traffic Flow Control in Automated Highway Systems" ,
Proceedings of the 8'h IFAC Symp. Transportation Systems, Chania Greece.
On
Bielli M., P. Carotenuto and V. Site, (1997) "Advanced Research on Transport-Environment Iteractions", Proceedings of the gh IFAC Symp. On Transportation Systems, Chania Greece. Broucke M . and P. Varaiya, (1997) "A Dynamic Model for Traffic Flow on Automated Highway Systems", Proceedings of the gh IFAC Symp. On Transportation Systems, Chania Greece. Bushnell L., B. Mirtich, A. Sahai and M. Secor, (1994) "Off-tracking Bounds for a Car Pulling Trailers with Kingpin Hitching", Proceedings of
Commission, Directorate-General for Transport, pp. I-50, Brussels. -d, (1994) "European Community, Framework Programme IV", Activity I , RTD and
the 33rri Conference on Decision and Control,
Demonstration
pp.2944-49, Lake Buena Vista, FL.
Brussels.
365
Programme
VI-Transport,
ROAD TRAINS OF REA VY TRUCKS AS RIGHW AY COMMERCIAL TRANSPORT ATION SYSTEMS
S. A. Manesis
Electrical and Computer Engineering Dept. Division of Systems and Control University of Patras [email protected]
Abstract: Today more than ever efforts of governments and companies try to provide safe and efficient transportation through air, over water and on land. Current highway transportation systems, except of the intelligent and automated aspect, do not present any other significant development especially concerning the "truck vehicle". This paper proposes the idea of long truck-trains with multiple semi-trailers as highway vehicle systems for freight transportation. The basic mechanical characteristics of the truck-train are described and the corresponding steering problems are introduced. The paper states also the path following problem and includes a discussion of the various traffic and steering rules that must be applied when a truck-train travels on a multi-lane highway. Copyright © 19981FAC
Keywords: Transportation systems, heavy trucks, vehicle trains.
1.
INTRODUCTION
al. (1994). Many other similar issues on the same topic (AHS) is the object of research (Horowitz, 1997; Mammar, 1997; Broucke and Varaiya, 1997; Alvarez, et ai., 1997; Hessburg and Tomizuka, 1994; Passino, 1995). In a classic example of developing new applications for remote sensing, the European Microwave Signature Laboratory is helping DaimlerBenz improve driver safety. The Institute for Remote Sensing Applications launched the ROCOCO (ROad COndition and COntrol) project in June 1995 with Daimler-Benz in order-as the partners hope-to reduce one day the traffic accidents (- a, 1995).
During the last decades transportation of people and goods has heavily increased. More demands than ever are recorded on airports, shipping lines, highways and railways. This situation as also the future requirements have led companies and governments to fmance several projects in order to improve their air and land transportation technology. A review paper (Dooling, 1996) provides an overview of today's directions in transportation technology. Modem air traffic control, safety against microbursts, terrific trains, smart ships, intelligent highway and global positioning system (GPS) are some of the keywords that express the innovative concepts in transportation.
Developed by European broadcasters and car radio manufacturers since the mid-1980s, Radio Data Systems (RDS) will play a major role in making road transport more efficient. Bosch and Philips companies began working on Traffic Message Channel (RDS-TMC) technology which enables thousands of coded traffic messages to be broadcast via RDS code (- b, 1996). In this way, RDS-TMC data providing updates on traffic, weather and more, road transport will flow even smoother. In USA on the other hand, in order to put highway traffic on a par with air traffic, a master plan for an Intelligent
In road transportation, the automated highway systems, the microprocessor-based vehicle controls, the road radars, the advanced GPS and the radio technologies are being applied - at research level until now - in all forms of passenger and freight transportation. The basic vehicle control issues that must be faced in designing a fully automated highway system (AHS) are described by Hedrick, et 361
Transportation System (ITS) was drawn by the corresponding US department. To San Antonio, Texas opened the country' s first municipal ITS while Colorado state dispose a smart highway exit (Interstate 70-Denver) which has a 9-Km downgrade where many runway trucks there have been over the last years. Sensors embedded in the roadway will enable computers to monitor truck speed and weight and to flash messages on roadside signs to warn drivers to slow down (Dooling, 1996).
TEN). In parallel, another RTD programme in the field of transport began in December 1994 which had a total budget of 240 Mecu and covered seven areas one of which was the road transport (- d, 1994). Although we note the above global effort for improvement of road transport conditions, in the field of freight transportation especially we have not a radical change of the predominant situation. We can say that it is characterized by the phrase "we see excellent highways full with excellent truck vehicles, so full that is dangerous to drive our car". As it is explained in the following chapters, the road freight transportation seems to have disadvantages against ship and railway transport. The paper proposes the introduction of "road trains" in the highway systems and international autobahns. The road trains will consist of a number of trailers (approximately 10-20) and a lead tractor. In order such a road train of trucks to be steerable with safety in a multi-lane highway a set of traffic rules must be defmed, the pathfollowing problem must be solved, the mechanical realization must be examined and the space limitations outside a highway must be taken care of. These aspects are some of the basic ones that are addressed in this paper.
A number of European projects concerning the transport policy have been elaborated during the last decade. In the 1980s vehicle manufacturers began to realize the limitations imposed by the increasing volume of vehicles in the European transport network. These limitations were due to urban congestion, increased cost from time devoted to travelling, accidents, safety, security, environmental pollution and the need to utilize the time spent on driving more efficiently. Subsequently, manufacturers envisioned the possibility of a new transport system based on the application and of electronics, computers and integration telecommunications to reduce these limitations. This gave birth to a research programme entitled PROMETHEUS (began in I986) consisting of three subprogrammes PRO-CAR, PRO-ROAD and PRONET. Later, it was established as an European Union backed EUREKA project (EU-45) investigating improvements in safety and efficiency on the roads. For a summary of PROMETHEUS' s aims as also of a parallel programme entitled DRIVE see (Nwagboso, I997).
2.
THE ROAD TRUCK TRAIN
The road freight transportation is performed today by several (more than 20) types of trucks as also by combinations of trucks, tractors and trailers. The longest of them are used in the case of international freight transportation between different countries. The four longest vehicle combinations are shown in Fig.1 and are coded as Tx-STy-Tz- .. . that means Tractor and Semi-Trailer and Trailer (stand alone) and ... , each with x,y,z, .. . axles correspondingly. There are also several types of rigid lead vehicles (RV) combined with trailers. All the above complex vehicles are usually driven by one or two drivers . In comparison with the other modes of freight transportation, ship and railway, truck vehicles seem to have an inherent disadvantage that is the small coefficient of useful weight per driver or in general per worker. For example, a medium size commercial
The European Commission's White Paper on "The Future Development of the Common Transport Policy" (CTP) was the first step towards defming goals of CTP and establishing the work programme to achieve them ( - c, I995). The ratification of the Treaty of Maastricht marked the beginning of a new phase for developing further the CTP. Also, it underlined the importance of the basic goals such as improvement in safety, sustainable growth respecting the environment integration of transport systems via intermodality and the quality and effectiveness of transport infrastructure (Trans-European Network-
T3-ST2-T2
T3-STl-T2-T2
T3-ST3
RV3-T3 Fig. l . The longest truck-trailer vehicles. 362
ship may transfer one hundred containers with only fifteen persons as crew. For road transportation of these containers, we need fifty RV3-T3 vehicles approximately, which require an equal number of drivers. The comparison is much more negative for truck vehicles if the ship is a large one. Similarly, a train with twenty railroad cars usually requires only two or three drivers .
[[:
... 1
El
IEI
method. The main advantages of using truck trains in highway freight transportation are the following: a) The aggregation of the multiple autonomous trucks in fewer (let more complex) truck trains. b) From the accident point of view, ten autonomous trucks in a high density autobahn are much more dangerous than a truck train with ten trailers.
IEI
IEI
IEI
II
Fig.2. The road truck train. During the last years, traffic in international autobahns has heavily increased following that in population centres. In order to face the difficulties of the high traffic density, several methods have been developed to increase safety and to optimize the throughput of highways. Various techniques on various topics concerning all kinds of car have this goal, as e.g. anti-lock brakes, AHS, collision avoidance strategies, sensor based driving, antiskidding robust control etc. (Horowitz, 1997; Mayr, 1997; Gissinger and Kortun, 1997; Bielli et al., 1997; Ackermann, 1997). Large truck vehicles occupy a significant percentage of the total traffic while they are increased day by day. In spite of the existent high-capacity autobahns, large truck vehicles it is expected to fill moreover them. Furthermore, they can achieve high speeds even with full load, and hence may cause accidents Gackknifmg leads out of control) especially under rainy and misty conditions.
c) The velocity of a truck train may be less than that of an autonomous truck but the fmal benefit will be of the truck train because of the multiple transported load. d) It is obvious that the vehicle emissions, noise and visual intrusion will be reduced. e) Major flexibility of the freight transportation system because of the interchangeability of the semi-trailers in the intermodal stations. f) Improvement of the safety because of the lower mean speed and of the stricter procedure for a lane change. The above concept of road truck trains imposes a series of problems concerning traffic, steering and control that will be introduced briefly in the following chapters.
A key to improving capacity and safety in an autobahn is the "hard platooning" of long truck vehicles that is a truck train. Soft platooning is the organization of groups of tightly spaced cars in an automated highway system. The truck traffic density in a highway is such that many platoons of truck vehicles are usually formed, especially in highways with few lanes. The simple dilemma is why these platoons of truck vehicles could not be a truck train in the form of a multi-trailer system. We can defme a truck train as the T5-nSn tractor/semi-trailer combination that is a high power tractor with five or more axles, which pulls n passive semi-trailers as shown in Fig.2. The number n may be assumed between 6 and 10 at first stage of development. We assume that the tractor has the required power to pull the semi-trailers and also that exist all the technical presuppositions which secure a smooth movement on the road. Another basic characteristic is that the kingpin hitch of each semi-trailer is on the center of the back pair of axles. This assumption is important for the application of an off-trucking elimination
The motion of a truck train in a multi-lane highway introduces a number of traffic problems. These are described in detail (Manesis, 1997). In this chapter, attention is focused only on the most significant of them. First of all, it must be clear that the truck trains are destined for movement only on multi-lane (;:: 3 in each direction) highways. When a truck train travels on a multi-lane highway problems arise due to the presence of other cars and needs for lane changes. As shown in Fig.3a, a crash may happen between the truck train and the private car since the car enters on the free side area of the train while it is changing lane. In this case, the known rule for left or write turn after a flash signal is not valid and a new one must be defmed. Another problem is that the driver of the long truck train can not estimate exactly, via his mirror, the distance of the side car and hence if it is inside the "effective area" of the train. In this case, a sensor based rule for a turn maneuver must been defmed. Fig.3b shows also that the classical overtaking is not permitted since the truck train encages the small car.
3. TRAFFIC RULES
363
It'
[: :1
It'
It'
It
-------------------------------------------------
(a)
(b) Fig.3. Examples of truck train traffic problems. the lead tractor during a turn at low speed. As in the case of a tractor pulling one semi-trailer, the offtracking is quantifIed successively for the last semitrailer in a convoy consisting of a tractor with more than five or ten semi-trailers. A closed-form expression for the off-tracking of the rear pivot point of a simple T3-STl vehicle can be found in (Alexander and Maddocks, 1988) while off-tracking bounds for a car pulling trailers have been derived in (Bushnell et al., 1994).
As already mentioned, the truck trains are destined to travel in autobahns between large towns and never inside them. In the peripheral zone of each town there will be a parking area adjacent to the autobahn where the truck trains will be composed/decomposed from/to individual semitrailers. These will be taken by independent local tractors in order to be transferred in the town, port or elsewhere. In the form of a container parking area, the truck train one will be a two-modal transportation station where simple semi-trailers will compose train vehicles and vice-versa. Consequently, every truck train is engaged in one of a fmite number of actions such as entering the highway, changing a lane, exiting the highway, temporary parking in a layby etc. The "travel" of the track train in a highway can be summarized by the sequence of actions that the complex vehicle executes. All the above problems can be faced and hence the "travel" of the truck train can be safe and effective, if we defme traffic rules with concrete priorities against other cars and actions in each case of traffic activity.
In the case of the proposed truck train, it is
imperative than any other case, e.g. classical trucktrailer vehicles, car-like multibody mobile robot and luggage carrier in an airport, that the last semi-trailer follows exactly the path of the lead tractor during a turn for lane change or a turn due to the curvature of the highway. Otherwise, it will be possible the last semi-trailer to violate the outer boundary of the highway or to crash with an adjacent car during a lane change although both keep invariant their relative velocity. The off-tracking problem has been studied by several authors; among the fIrst were Ervin and Guy, (1986). The case of equal length kingpin hitches (the kingpin between the bodies of the vehicles) has been simulated by Bushnell et al., (1994) but can not be applied to heavy duty trucks and trailers. On the other hand, steerable trailers are of increasing interest because they can make turns around corners more manageable but have been studied mainly for the case of one rear axle equipped with steerable wheels and for one trailer. A multisteering and multitrailer
4. THE OFF-TRACKING PROBLEM
The steering of a long truck train on a multi-lane highway will be a major problem in terms of public safety and traffic smoothness. Among the various truck train maneuverability and stability problems, the most basic will be the so-called off-tracking one and is the fIrst that we must face. Off-tracking is defmed as the deviation of the semi-trailers' axles or the kingpin hitch from the path of the steering axle of 364
system has been studied by Tilbury et al., (1995) from the kinematic model point of view, which can not be applied in the case of a truck train. Furthennore, if a steerable trailer technique is going to be applied in a heavy trailer with two or three rear axles then it seems that it will be an expensive solution.
Dooling D., (1996) "Transportation", IEEE SPECTRUM, January pp.82-86. Ervin R.D. and Y.Guy, (1986) "Axioms relating size and weight constraints to the response of trailers in combination trucks", Int. Symp. on Heavy Vehicle Weights and Dimensions, Ottawa Canada. Gissinger G.L. and W. Kortun, (1997) " Simulation of Vehicle System Dynamics, State of the Art and Ongoing Developments", Proceedings of the gh IFAC Sy mp. On Transportation Systems, Chania Greece. Hedrick J.K. , M. Tomizuka and P. Varaiya, (1994) " Control Issues in Automated Highway Systems", IEEE Control Systems, pp.21-32. Hessburg T. and M. Tomizuka, (1994) "Fuzzy Logic Control for Lateral Vehicle Guidance", IEEE Control Systems, pp.55-63. Horowitz R., (1997) "Automated Highway Systems: The Smart Way to Go", Proceedings of the gh IFAC Symp. On Transportation Systems, Chania Greece. Mammar S., (1997) "Robust Automatic Steering of a Vehicle: an LMI approach", Proceedings of the
The off-tracking is eliminated by sliding each trailer with respect to the previous, a technique described in (Manesis, 1998). According to this, the kingpin hitch in each semi-trailer slides in a direction perpendicular to the longitudinal axle of the trailer. The sliding width varies as a linear or exponential function of the front wheel turning angle. A basic assumption of the method in order to be applicable is that the lead tractor doesn ' t perfonn sharp turns. In the case of the truck train, this is satisfied because the radius of curvatures of the highways is not pennitted to be less than 700 m. Then, as it is pointed out the required sliding width doesn't exceed 25 cm. By eliminating the off-tracking, the driver of the truck train doesn' t need anymore to turn far to the desired path because of the path deviation of the rear trailers.
8'h IFAC Symp. On Transportation Systems, Chania Greece. Manesis S., (1997) "On highway trafficability and followability of extra long trucks with multiple semi-trailers", Technical report, Systems and Control Division, University of Patras, Greece. Manesis S., (1998) "Off-tracking elimination in road trains of heavy duty trucks with mUltiple semitrailers", Proceedings of the gh IFAC Symp. On Large Scale Systems: Theory and Applications LSS'98, Patras Greece. Mayr R. , (1997) "Driving Comfort in Sensor Based Lateral Vehicle Control", Proceedings of the gh IFAC Symp. On Transportation Systems, Chania Greece. Nwagboso c., (1997) "Advanced Vehicle and Infrastructure Systems: Computer Application, Control and Automation", 1. Wiley & Sons. Passino K.M., (1995) "Intelligent Control for Autonomous Systems", IEEE SPECTRUM, pp.55-62. Tilbury D., 0.1. Sordalen, L. Bushnell and S. Shankar, (1995) "A Muitisteering Trailer System: Conversion into Chained Fonn Using Dynamic Feedback", IEEE Trans. on Robotics and Automation, pp.807-817, voUI, No.6. -a, (1995) "IRSA: Radar on the road", Innovation and Technology Transfer, pp.l9, vol.5 . ~, (1996) "Wiring the Roads" , Innovation Technology Transfer, pp. 13, vol.2 . --c, (1995) "The Common Transport Policy Agenda 1995-2000: An action programme towards sustainable mobility in Europe", European
5. CONCLUSIONS Ground transport, both public and private, will continue to develop to meet perceived social and economic needs; technological changes are undoubtedly expected. In this paper the concept of truck trains as highway transportation systems is proposed. The basic aspects and problems arising from such a technical challenge have been presented.
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Bielli M., P. Carotenuto and V. Site, (1997) "Advanced Research on Transport-Environment Iteractions", Proceedings of the gh IFAC Symp. On Transportation Systems, Chania Greece. Broucke M . and P. Varaiya, (1997) "A Dynamic Model for Traffic Flow on Automated Highway Systems", Proceedings of the gh IFAC Symp. On Transportation Systems, Chania Greece. Bushnell L., B. Mirtich, A. Sahai and M. Secor, (1994) "Off-tracking Bounds for a Car Pulling Trailers with Kingpin Hitching", Proceedings of
Commission, Directorate-General for Transport, pp. I-50, Brussels. -d, (1994) "European Community, Framework Programme IV", Activity I , RTD and
the 33rri Conference on Decision and Control,
Demonstration
pp.2944-49, Lake Buena Vista, FL.
Brussels.
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Programme
VI-Transport,