Delft University of Technology
FACULTY MECHANICAL, MARITIME AND MATERIALS ENGINEERING
Department Marine and Transport Technology Mekelweg 2 2628 CD Delft the Netherlands Phone +31 (0)15-2782889 Fax +31 (0)15-2781397 www.mtt.tudelft.nl
Specialization: Transport Engineering and Logistics Report number: 2015.TEL.7932
Title: Vehicle routing for container transport between quay cranes and stack
Author: T.J.W. Bentvelsen
Title (in Dutch) Voertuig routering voor container transport tussen kade kranen en opslag
Assignment: Literature Confidential: No
Initiator (university): Ir. M.B. Duinkerken Initiator (company): TU Delft
Supervisor: Ir. M.B. Duinkerken
Delft University of Technology
FACULTY OF MECHANICAL, MARITIME AND MATERIALS ENGINEERING
Department of Marine and Transport Technology Mekelweg 2 2628 CD Delft the Netherlands Phone +31 (0)15-2782889 Fax +31 (0)15-2781397 www.mtt.tudelft.nl
Student: T.J.W. Bentvelsen Assignment type: Literature Supervisor (TUD): Ir. M.B. Duinkerken Creditpoints (EC): 10
Supervisor (Company): TU Delft Specialization: TEL
Report number: 2015.TEL.7932 Confidential: No
Subject: Vehicle routing for container transport between quay cranes and stack.
From a historical perspective, two different terminal design concepts can be considered. Traditionally, terminals were constructed according to the parallel design layout, which incorporates blocks that are parallel to the main quay of the terminal. The majority of all container terminals worldwide thus have their design based on this principle. Different types of equipment are used to handle the flow of containers between the quay cranes and the stack, but the routing of these vehicles is often subject to interference from landside traffic.
Changes in terminal design have led to the development of the perpendicular oriented container terminal. Here, containers are stored perpendicular with respect to the terminal main quay. This innovative design has only been applied on a select amount of terminals worldwide, more often than not combined with principles from the field of automation. A perpendicular layout lends itself perfectly to the usage of Automated Guided Vehicles (AGV’s) or Automated Lifting Vehicles (ALV’s), in combination with Automated Stacking Cranes (ASc’s). Some terminals have even adopted technologies that allow partial automation of quay crane operations. Unique to this design is that it can be applied such that landside vehicles are absent from the apron of the terminal. Storage facilities on these terminals act as a decoupling mechanism in order to separate landside traffic and waterside traffic. This is however not a requirement.
Although the perpendicular design may seem promising due to its innovativity, there is a general consensus amongst traditional terminal operators that terminals with a perpendicular orientation have a lower productivity and require a larger area for operation.
For this literature assignment, it will be investigate how the waterside vehicle routing on container terminals can be improved. Both manned and unmanned vehicles should be reviewed in the assignment. During the assignment, two questions are of particular interest:
Which methods are used for the routing of vehicles on the waterside?
Which solutions exist to solve the problems that arise when both manned and unmanned vehicles operate in the same area?
It is expected that you conclude your literature assignment with a written report, including conclusions and recommendations for future research. The report must be written in English and must comply with the guidelines of the department. Details can be found on Blackboard.
Preface
During a study tour to the Socialist Republic of Vietnam and the Republic of Korea, different ports and container terminals were visited, of which both automated and con-ventional terminals. The visits sparked an interest in the differences between the two types of container terminals as both claimed their set-up was preferred over the other. From this interest and some discussion with the accompanying teacher, this literature study was established.
The report contains the literature study into the routing of manned and unmanned ve-hicles on container terminals. The study focusses on the horizontal transportation of containers that occurs between the waterside of the terminal and the container stack. The assignment is completed for the master specialization Transport Engineering and Logistics, part of the faculty Mechanical Engineering at the Delft University of Technol-ogy.
People new to the topic of container terminals and the routing of vehicles are encouraged to read this report. An overview of typical container terminals is given in chapters 3, 4 and 5. More experienced readers may want to read the analysis of existing routing meth-ods that is performed in chapter 6 and possibilities for improvement that are discussed in chapter 7.
As a final comment, I would like to express my gratitude to M.B. Duinkerken for pro-viding guidance during the assignment and finding the time to have discussions with me on this topic. Secondly, M. Coeveld provided valuable insights into container terminals at the start of this study, which I am very thankful to.
Abstract
As containerization and globalization have led to a growth of 10% for containerized freight each year, the recent international economic crisis has diminished interest in constructing automated ports. Terminal operators now aim to provide a more economic service with flexible capacities. To find improvements for automated container terminals, a study into the routing of unmanned vehicles is performed. Several sources are used for publications discussing vehicle routing problems, which are found by combining various keywords in search engines for scientific articles.
To correctly investigate the routing of vehicles, the typical container terminal is described with accompanying functions and operations. For container transport, the stacking of containers, orientations of the stack and transfer method are of importance. Hence, the different types of equipment are categorized into horizontal transport equipment and yard handling equipment. The different types of equipment could then be combined into generic terminal concepts, which typically occur in real world situations. When available, the dimensions of such layouts are illustrated.
With the information of previous chapters, a detailed overview of the aspects for vehicle routing is given. Publications that discuss vehicle routing algorithms are categorized according to these aspects, as well as the routing method itself, in Table 6.1. Three methods exist, fixed topology static routing, fixed topology dynamic routing and free ranging dynamic routing. Among the articles, a distinction is made between the physical and the logistic side of each routing method.
The conclusion is drawn that little information is available of free ranging vehicle routing, and that improvements to this method can be taken from other fields. Examples are the autonomous road vehicles, which allow for the emulation of manned vehicles, and mobile robot trajectory planning, which could learn vehicles to circumvent static and moving obstacles.
V
Further research into this and related topics is recommended. The potential of free ranging systems should be investigated, as does its performance compared to other routing algorithms. Autonomous vehicle developers can be contacted for information on the routing of vehicles and obstacle recognition, however it is expected that the information remains confidential. Therefore it could prove useful to study the traffic rules for manned vehicles on existing container terminals.
Abstract (Dutch)
Door een toename in de mondialisering en het gebruik van containers, groeit het goed-erenvervoer met containers ieder jaar 10%. De recente internationale economische crisis heeft echter de bouw van geautomatiseerde container terminals teruggedrongen. Er wordt nu gestreefd naar het aanbieden van een dienst die betaalbaar is en voorziet in een flexibele capaciteit. Om geautomatiseerde container terminals te verbeteren, wordt in deze studie onderzoek gedaan naar de routering van onbemande voertuigen. Verschil-lende bronnen worden gebruikt bij het zoeken naar publicaties die voertuig routerings problemen bespreken. In de zoekmachines worden combinaties van verschillende wo-orden die toepasselijk zijn voor container terminals gebruikt om zo wetenschappelijke artikelen te vinden.
Om de routing van de voertuigen op een juiste manier te onderzoeken, is een karak-teristieke container terminal met bijbehorende functies en operaties beschreven. Voor het container transport zijn de methode van container stapelen, de oriÃńntatie van de stapel en de overdrachtsmethode van belang. Om dit verder uit te werken, zijn de ver-schillende soorten apparatuur onderverdeeld in horizontale transportmiddelen en stapel systemen. De twee soorten zijn vervolgens gecombineerd tot generieke terminal con-cepten, die karakteristiek zijn voor de werkelijkheid. Wanneer deze beschikbaar waren, zijn de afmetingen van dergelijke concepten geïllustreerd.
Een gedetailleerd overzicht van de aspecten voor route planning is gegeven, afgaande op de informatie uit de voorgaande hoofdstukken. De wetenschappelijke publicaties die voertuig routeringalgoritmes beschrijven zijn op basis van deze aspecten ingedeeld, te zien in 6.1. Tevens konden de artikelen gecategoriseerd worden op methoden: vaste topologie met statische routering, vaste topologie met dynamische routering en vrije dynamische routering. Bij iedere methode is onderscheid gemaakt tussen fysieke en logistieke routeringmethoden.
VII
vrije dynamische routering. Het verbeteren van deze methode kan worden gedaan met expertise uit andere onderzoeksvelden. Met name de domeinen autonome weg voer-tuigen, die het voor automatische voertuigen mogelijk maken bemande voertuigen te imiteren, en mobiele robot traject planning, welke voertuigen kan leren statische en be-wegende objecten te herkennen, kunnen een rol spelen in de ontwikkeling van voertuigen op automatische container terminals.
Verder onderzoek naar dit en aanverwante onderwerpen wordt sterk aanbevolen. Het potentieel van vrije routeringmethodes moeten worden onderzocht, evenals de prestaties van de methode vergeleken met andere routeringalgoritmen. Ontwikkelaars van au-tonome auto’s kunnen worden gecontacteerd voor informatie over de routering van vo-ertuigen en het herkennen van obstakels. De verwachting is echter dat die informatie vertrouwelijk blijft. Daarom kan het nuttig blijken om de verkeersregels voor bemande voertuigen op bestaande container terminals te bestuderen.
Nomenclature
AGV Automated Guided Vehicle ALV Automated Lifting Vehicle AMO Autonomous Moving Objects
ARMGc Automated Rail-Mounted Gantry crane ASc Automated Stacking crane
AShC Automated Shuttle Carrier AYC Automated Yard Crane
CTA Container Terminal Altenwerder
HHLA Hamburger Hafen und Logistik Aktiengesellschaft MTS Multi-Trailer System
OHBc OverHead Bridge crane PoLA Port of Los Angeles
QC Quay Crane
RMGc Rail-Mounted Gantry crane RTGc Rubber-Tyred Gantry crane SC Straddle Carrier
ShC Shuttle Carrier STSc Ship-To-Shore crane
TEU Twenty-foot Equivalent Unit TSP Travelling Salesman Problem TTU Truck-Trailer Unit
VRP Vehicle Routing Problem
VRPB Vehicle Routing Problem with Backhaul
VRPFC Vehicle Routing Problem with Full Container load WSGc Wide-Span Gantry crane
Table of Contents
Preface III Abstract IV Abstract (Dutch) VI Nomenclature VIII 1 Introduction 1 2 Methodology 3 2.1 Background information . . . 3 2.2 Vehicle routing . . . 42.3 Improving vehicle routing . . . 4
3 A typical container terminal 6 3.1 Primary functions and operations . . . 6
3.2 Aspects influencing terminal operations . . . 8
3.2.1 Stacking of containers . . . 8
3.2.2 Yard transfer . . . 9
3.2.3 Layout orientation . . . 9
4 Container handling equipment 12 4.1 Introduction . . . 12
4.2 Horizontal transport equipment . . . 13
4.3 Yard handling equipment . . . 15
X Table of Contents
5 Generic terminal concepts 18
5.1 Equipment implementation . . . 18
5.1.1 Reachstacker with Truck-Trailer Units . . . 18
5.1.2 Straddle Carrier system . . . 19
5.1.3 Rubber-Tyred Gantry crane with Truck-Trailer Units . . . 20
5.1.4 Rail-Mounted Gantry crane with manned vehicles . . . 20
5.1.5 Rail-Mounted Gantry crane with unmanned vehicles . . . 21
5.2 Influencing factors . . . 23
6 Vehicle Routing 25 6.1 Aspects of vehicle routing . . . 26
6.2 Routing methods . . . 28
6.3 Overview of literature regarding vehicle routing . . . 29
6.3.1 Fixed topology static routing . . . 30
6.3.2 Fixed topology dynamic routing . . . 34
6.3.3 Free ranging dynamic routing . . . 37
7 Improvements to vehicle routing 38 7.1 Autonomous vehicles . . . 38 7.1.1 DARPA . . . 39 7.1.2 Google Car . . . 39 7.1.3 Automobile manufacturers . . . 39 7.2 Mobile robots . . . 40 7.3 Future developments . . . 41
7.3.1 Manned and unmanned vehicle interaction . . . 41
7.3.2 Improve free range physcial routing . . . 41
8 Concluding remarks 42 8.1 Main research question . . . 42
8.2 Discussion . . . 43
8.3 Recommendations . . . 45
Bibliography 54 Appendix A Interview TBA 55 Appendix B Literature summaries 76 B.1 Fixed topology static routing . . . 76
B.2 Fixed topology dynamic routing . . . 79
List of Figures
3.1 A typical layout of a container terminal (see Kemme (2012), p.18). . . 7
3.2 Different block structures with transfer methods (see Wiese et al. (2011), p.225). . . 9
3.3 Parallel layout of a terminal with RTGc system (see Kemme (2012), p.69). . 10
3.4 Perpendicular layout of a terminal with RMGc system (see Kemme (2012), p.72). . . 10
4.1 A Tractor-Trailer Unit at the terminal apron (Gatic, 2008). . . 13
4.2 Multi-Trailer System in operation (Doorn Containers, 2011). . . 13
4.3 Two Straddle Carriers at a storage yard (Hivemind, 2009). . . 14
4.4 A Shuttle Carrier (Port Strategy, 2012). . . 14
4.5 Automated Shuttle Carriers at a stack (Port Strategy, 2013). . . 14
4.6 AGV’s at Hamburg Hafen CTA (Terex, 2009). . . 14
4.7 Automated Lifting Vehicles (TotaalTrans, 2014). . . 15
4.8 A Reachstacker (TotaalTrans, 2011). . . 16
4.9 Empty Container Handler (Wikipedia, 2010). . . 16
4.10 Rubber-Tyred Gantry crane (Kone Cranes, 2012a). . . 16
4.11 Rail-Mounted Gantry crane (Wikipedia, 2011). . . 16
4.12 A Wide-Span Gantry crane with cantilever (Kone Cranes, 2012b). . . 17
4.13 An Overhead Bridge crane (Whiting Corp, 2007). . . 17
XII List of Figures
5.2 Cross section of a typical automated terminal quay (see Ranau (2011), p.184). 21 5.3 Dimensions of a perpendicular layout AGV or ALV system (see Ranau (2011),
p.190). . . 22 5.4 Dimensions of a perpendicular ShC or AShC system (see Ranau (2011), p.191). 23 6.1 Grid guide-path network for a perpendicular container terminal layout (Jeon
et al., 2011). . . 32 6.2 An illustration depicting a mesh layout solution from Lin et al. (2011). . . 33 6.3 Screen snapshot of a simulation by Bae et al. (2011) showing routes and
vehicle movements on a perpendicular automated container terminal. . . 35 6.4 Overlapping of physical routes of AGV’s (Bae et al., 2011). . . 35 6.5 Dimensions of a perpendicular AGV sytem (left) and ALV system (right) (Bae
et al., 2011). . . 35 6.6 Screenshot of the DEFT simulation for free ranging vehicles (Duinkerken
et al., 2012). . . 37 7.1 One of the 24 self-driving test vehicles operated by Google (City Lab, 2014). 40
List of Tables
4.1 Summary of the functionality for each equipment type, as well as loading
capability (see Brinkmann (2011), p.25-39). . . 17
6.1 Overview of literature concerning the routing of vehicles. . . 31
6.2 Overview of literature regarding fixed topology static routing. . . 34
6.3 Overview of literature regarding fixed topology dynamic routing. . . 37
Chapter 1
Introduction
Containerization and globalization are important factors that caused an increase of tainerized freight. Collectively, all factors have led to an annual growth rate for con-tainerized freight of over 10% for a sustained number of years (Kemme, 2012).
In a publication by the Hamburger Hafen und Logistik Aktiengesellschaft (HHLA), it is observed that due to the international crisis in 2008 and 2009, terminal operators now tend to focus on providing a more economic service. They ideally combine this with flexible capacities. This is contrary to enlarging the capacity of a terminal, an objective that was pursued prior to the crisis (HHLA, 2009). In an interview with Martijn Coeveld, Managing Director of TBA (see Appendix A), it was noted that an increased interest in (partial) container terminal automation was present before the crisis. This interest declined during the course of the international economic crisis.
Likewise, there is a general consensus amongst traditional terminal operators that having a perpendicular block orientation leads to lower productivity and requires more space at the waterside traffic area. This argument may be one of the reasons why corporate interest in terminal automation has diminished since.
Researchers from various disciplines have investigated the topic of container terminals extensively, offering a broad perspective of specializations. Regarding the observations of previous paragraphs, this literature study sets out to collect important works involving this topic in order to find:
What characteristics describe the routing of manned and unmanned vehicles at the waterside for the adopted container terminal layouts and how can automated vehicle routing be improved?
The definition of vehicle routing is somewhat ambiguous, it can be regarded as a physical or as a logistical problem. With the physical routing is meant the actual path from one
2 Introduction
point to another. The logistical problem describes how vehicles are best to serve multiple origins and/or destinations. This misconception could lead to confusion amongst those interested in this study. In order to eliminate the risk, this research is focussed on the physical aspects of vehicle routing and indicates which definition authors maintain in the cited publications.
It should also be noted that waterside traffic is interwoven with other activities at the container terminal such as container storage handling and the external traffic interfering with internal traffic. Therefore a partial overlap with these areas is to be expected. To ensure the completeness of this report, several secondary questions are of importance and will be elaborated in chapter 3 through chapter 7 respectively.
• What operations are performed on a container terminal?
• What types of equipment exist on container terminals for transport between the quay and stack?
• Which generic terminal concepts are created when equipment is coupled? • Which methods are available to route the traffic on the terminal?
• Which solutions exist to improve vehicle routing for unmanned vehicles?
To address all the secondary questions, the outline of the literature study will be as follows; chapter 2 describes the approaches that are used in order to obtain the necessary information for different parts of this literature study. The context of this study is then elaborated subsequently in chapter 3, chapter 4 and chapter 5. The first of these chapters introduces a typical container terminal with associated primary functions and operations. In chapter 4 is then discussed which equipment types are available for the handling of containers, whereafter chapter 5 elaborates on the terminal layout designs with typical compositions that combine different equipment types into a functioning design. When the context of the study is discussed, the routing of vehicles is represented in chapter 6. In the chapter, publications are categorized and methods are elaborated. Chapter 7 then investigates how the free ranging vehicle system can benefit from available methods. To finalize this study, chapter 8 provides the concluding remarks to the study and discusses the results.
Chapter 2
Methodology
During this research, different approaches will be applied in order to obtain the necessary information to construct a complete portrayal of a container terminal. This chapter is subdivided into three parts which describe the link between the subject of a chapter and the methodology that will be used to obtain information. Each method is explained in the chapter to ensure the correctness of the method and information.
In section 2.1 is elaborated how the background information will be obtained which spans chapters 3, 4 and 5 with the first three secondary questions from chapter 1 on terminal operations, equipment types and terminal concepts. Hereafter, section 2.2 elaborates on the method to find literature concerning the topic of vehicle routing at container terminals. This part is identified with the fourth secondary research question. To finalize the chapter, section 2.3 describes the method for finding technologies from other fields to improve vehicle routing and with it answering the fifth secondary research question.
2.1
Background information
Starting with a search through the TU Delft Library, a large variety of subjects that concern with container terminals is found. The library system includes the repository of works published by experts associated with the Delft University of Technology. The information required to describe what operations are performed on container terminals from chapter 3 is searched with the terms container*, freight*, terminal*, function* and
operation*. References from the found articles are also scanned for relevancy and are
included in the chapter. The chapter is mainly based on Saanen (2004), Böse (2011) and Brinkmann (2011).
4 Methodology
Describing the functions and operations at a container terminal for chapter 3, further information is required which describes what types of equipment that exist for the trans-port of containers between quay crane and stack. This is elaborated upon in chapter 4 with information that is obtained by a search for publications containing: container*,
freight*, cargo*, terminal*, equipment*, vehicle* and transport*, performed in the TU
Delft Library. Additionally, the search expands to Science Direct for supplementary ma-terial. Bruns et al. (2007), Carlo et al. (2014), Vis and de Koster (2003) and Steenken et al. (2004) are the main contributors to this topic.
By coupling the two equipment types, different terminal concepts are created. To find which generic terminal concepts are created, the following search terms are used for the information in chapter 5: container*, terminal*, planning*, layout* and design*. Both TU Delft Library and Science Direct are consulted in the search. Generic layouts are retrieved from Kemme (2012) and Brinkmann (2011) whilst several more detailed layouts are described by Ranau (2011).
2.2
Vehicle routing
To find the methods which are available to route the traffic on container terminals, elaborated in chapter 6, a search was performed in Science Direct, Web of Science and SpringerLink for articles containing a combination of the words: container*, terminal*,
transport*, automat*, vehicle*, AGV*, rout*. To reduce the number of articles, only
en-tries from 2008-2014 are selected, as it is assumed that Steenken et al. (2004), Stahlbock and Voß (2008) and Vis (2006b) have addressed all other relevant articles in their re-search. Pillac et al. (2013) and Fazlollahtabar and Saidi-Mehrabad (2013) have only investigated dynamic routing problems and are therefore considered incomplete for this literature research.
The search in Science Direct, Web of Science and SpringerLink yielded 88, 66 and 62 results respectively. Whether the abstract and conclusion of the article will be read is determined by the relevancy of the articles title. After the conclusion has been read, it is determined if the full article will be read or that the article is irrelevant. Only by reading the full text will the article be included in this literature study as a source. Articles to which is referred in the publications are also included in the process.
Two interesting publications could not be fully obtained due to confidentiality. Both ar-ticles, Dkhil et al. (2013) and Zhao and Goodchild (2011), have been classified according to the available abstract.
2.3
Improving vehicle routing
The last part of this study, chapter 7, focusses on finding the solutions that exist to improve vehicle routing with existing mechanisms. In the search for vehicle routing
2.3 Improving vehicle routing 5
methods, described in section 2.2, it is found that little research addresses free ranging vehicles. This led to a search for alternatives from other fields that could improve the existing theories. It is focussed on autonomous vehicles as free ranging vehicles mimic manned vehicles and can thus be improved.
The search is performed in Google, with the following search queries: autonomous
vehi-cle, self driving vehivehi-cle, self driving car, automated vehicle and vehicle interaction. With
this search, the possibilities from other research fields that are present at this moment are explored. The chapter therefore only elaborates on the potential improvements it could bring to free ranging vehicles.
Chapter 3
A typical container terminal
In order to comprehend and elaborate on the description of container terminals, it is first necessary to describe the functions and operations of a typical container terminal. This is performed in the first part of this chapter, section 3.1, and will depict a typical container terminal. Hereafter the aspects that influence operations are discussed in section 3.2.
3.1
Primary functions and operations
According to Saanen (2004), a terminal has two specific primary functions and several secondary function. These secondary functions can be summarized as added services for terminal customers. The primary functions are:
• Transshipment of containers between different modes of transport • Temporary storage of containers
When the primary functions are investigated further the terminal can be partitioned into different operational areas, depicted in 3.1. Each area has its own set of functions which are described by Böse (2011). A short recollection of the quayside, yard and landside operations is presented hereunder.
Quayside operations are responsible for the loading and discharging of the vessel, affiliated with the transshipment of containers. To complete this operation, a han-dover between other terminal equipment is necessary. The horizontal transport of containers between the quay and stack is also considered to be a part of the quay-side operation. Figure 3.1 depicts this as ship-to-shore and waterquay-side horizontal transport.
3.1 Primary functions and operations 7
Figure 3.1: A typical layout of a container terminal (see Kemme (2012), p.18).
Yard operations are involved with the container transport and stacking within the storage area. Because the handover between horizontal transport equipment and yard equipment requires interaction between them, it is also a responsibility of the yard operation. To ensure that the necessary containers are easily accessible, housekeeping of the storage blocks is performed at the yard. Kemme (2012) clas-sifies the empty container depot, maintenance and repair as part of the secondary yard operations. The primary operation of the yard is the storage of containers.
Landside operations circumscribe the handling of containers from or to the barge ter-minal, rail terminal and truck handling facilities. These are related to the primary function; transshipment of containers between different modes of transport. Simi-larly to the other operational areas, the landside operation involves the handover between transport equipment and stacking equipment. Since the landside handles the hinterland connection (see Figure 3.1), it is responsible for the checking of in-bound and outin-bound containers and their corresponding data. Checking however, is not considered in this study.
8 A typical container terminal
According to the 3-Level-Model adapted for Terminal Planning (Böse, 2011), consisting of three pillars describing the fundamental tasks of container terminal planning, the planning of terminal operations can be subdivided into short-term, medium-term and long-term planning. These correspond with operational, tactical and strategic decisions and measures respectively.
Operational decisions and measures affect the day-to-day process on the terminal. An example of this type is the way in which is dealt with traffic congestion on a particular day.
Tactical decisions and measures influence how the basic terminal resources are used and co-operation between different organizations. Implementing a system allowing for vehicle pooling on the terminal is a tactical measure.
Strategical decisions and measures determine which terminal services are offered and how this is achieved. It also involves which long-term partnerships will be formed. The maximum achievable berth capacity would be an example of a strate-gical decision.
3.2
Aspects influencing terminal operations
As was previously mentioned, this study will focus on the routing of traffic between the quay crane and the storage area. This involves quay operations and yard operations, which are described in section 3.1. Aspects which influence these operational areas are the length, width, height, orientation and transfer method of the storage yard, as well as the position of the cranes located at the terminal quay. Horizontal transport equipment merely navigates around these obstacles for an efficient route. The first section, sub-section 3.2.1, discusses the different stacking availabilities. Hereafter, subsub-section 3.2.2 regards the alternatives that are present for the transfer of containers to the stack. Finally, subsection 3.2.3 discusses the orientation of the terminal layout.
3.2.1 Stacking of containers
Brinkmann (2011) concludes in her work that containers on the terminal can either be stored in lanes or in blocks. Kemme (2012) similarly classifies both stacking types. For block storage, the amount of rows, bays and tiers needs to be defined (see Figure 3.2). Two goals are defined by Lee and Kim (2010) that are important for the dimensions of the blocks. These are to maximize the throughput and to maximize the storage capacity. According to Petering and Murty (2009) the amount of bays is ideally between 57 and 72 slots for RTGc’s, RMGc’s and OHBC’s. The width depends on the type of equipment that is used. Blocks can be oriented parallel or perpendicular with respect to the terminal quay. This is discussed in subsection 3.2.3.
3.2 Aspects influencing terminal operations 9
Figure 3.2: Different block structures with transfer methods (see Wiese et al. (2011),
p.225).
Storage lanes are similar to storage blocks with a width of one. Since lane storage only takes place on terminals which operate Straddle Carriers or store containers on chassis, which happens mostly in North America (Steenken et al., 2004), the orientation of these lanes is arbitrary. For Straddle Carriers there is however a preference to positioning lanes perpendicular, since it only requires a 90 degrees turn from the main quay (Chu and Huang, 2005).
According to Steenken et al. (2004), some stack areas are reserved for special containers like reefers, which need an electrical connection. Simulation has shown that spreading the reefer positions over several stacks yields a higher throughput. Containers with dangerous goods, over-width and over-height containers are stored in a separate area.
3.2.2 Yard transfer
In the case of storage blocks, container transfer can take place in two ways. The first way is by transfer lanes. Here, one row of a block structure is reserved for the handling of trucks. This is more common with RTGc’s. Petering and Murty (2009) mentions that it is likely that RTGc’s will use transfer lanes, since these cranes cannot gantry properly while carrying a container. Contrary to this, the RMGc’s mostly apply transfer points at the front and end of the stack. Because these cranes run on rail tracks, the gantry operation is performed more easily. Figure 3.2 indicates the three options: transfer lanes and transfer points for Gantry cranes and storage lanes for the Straddle Carriers system.
3.2.3 Layout orientation
Excluding the storage lanes for Straddle Carriers and truck chassis, storage blocks on a container terminal are typically oriented either parallel or perpendicular to the main quay (Brinkmann, 2011; Kemme, 2012). Figures 3.3 and 3.4 show the parallel orientation and perpendicular orientation respectively. Varying types of equipment can be used on both orientations, although literature indicates that certain compositions are preferred.
10 A typical container terminal
Figure 3.3: Parallel layout of a terminal with RTGc system (see Kemme (2012), p.69).
Figure 3.4: Perpendicular layout of a terminal with RMGc system (see Kemme (2012),
3.2 Aspects influencing terminal operations 11
These are discussed in section 5.1. Figure 3.3 shows that access roads are placed in a mesh around the storage blocks. This can also be applied on perpendicular layouts. It should be noted that the layouts are generalized and certain real world terminal oper-ators will combine and adapt these layouts to their preferences, such that the terminal is optimised for that specific location. An example of this would be the TraPac Terminal at the port of Los Angeles. At this terminal, different ideas are combined in order to meet the demands of the location. Automated Shuttle Carriers are used to transport contain-ers from the quayside to the Automated RMGc’s. The orientation of these RMGc’s are mostly perpendicular to the quay, but as an exception, four blocks are placed parallel to the quay. The terminal even uses the Shuttle Carriers to store a small amount of containers in lanes. Because the paper from DiMeglio and Sisson (2013) was unavailable for public access, a promotional video from Port of Los Angeles (2014) was viewed for this specific information.
Chapter 4
Container handling equipment
With the functions and operational areas of a typical container terminal provided in chapter 3, this chapter elaborates on the different equipment types that are used at container terminals. By doing so, it becomes clear on which types should be focussed in order to comply to the research question. A short introduction on the topic of this chapter is given in section 4.1 which partitions vehicles into two main categories:
• Horizontal transport equipment • Yard handling equipment
The horizontal transport equipment is investigated in section 4.2 whereas the yard han-dling equipment is discussed in section 4.3. Section 4.4 then provides an overview of the equipment.
4.1
Introduction
There are several different kinds of equipment used on container terminals. Each has its own function and specialization. Specific types of equipment however can have over-lapping functions. Because this literature study focusses on the waterside traffic, only horizontal transport equipment of the terminal is reviewed in combination with the yard equipment, as both types of equipment can be interdependent.
For the operation of vehicles on container terminals, it is important to recognize whether they have active loading or passive loading. A passive loading vehicle requires other terminal equipment to assist with container loading. These vehicles cannot operate without the need of loading equipment. Active loading vehicles however do not need
4.2 Horizontal transport equipment 13
Figure 4.1: A Tractor-Trailer Unit at the
terminal apron (Gatic, 2008).
Figure 4.2: Multi-Trailer System in
op-eration (Doorn Containers, 2011).
assistance from other equipment. These vehicles can load themselves, transport and unload the containers.
In the following parts, a short description for each vehicle is given and mentioned whether the vehicle has active loading or passive loading. To maintain an overview of the vehicles, they are subdivided into the category concerning their most important function, hori-zontal transport or yard handling, section 4.2 and section 4.3 respectively. An overview of this is given in Table 4.1. As was mentioned, some equipment can have both functions.
4.2
Horizontal transport equipment
The horizontal transport equipment is used to transport containers from the quayside to the yard or vice versa. The information was obtained from Bruns et al. (2007), Carlo et al. (2014), Vis and de Koster (2003), and Steenken et al. (2004).
Tractor-Trailer Unit (TTU) A single trailer is pulled by a tractor. The trailer can be loaded with two Twenty-foot Equivalent Units (TEU). The vehicle is used to transport containers to or from the container stack from several locations such as the quayside, train terminal or barge terminal. This vehicle type is loaded passively, as can be seen in Figure 4.1. Some terminals use the chassis (trailers) of these trucks to store containers in the yard.
Multi-Trailer System (MTS) A tractor pulls a series of trailers, and each trailer can be loaded with two TEU. This vehicle has the same purpose as the TTU and is also loaded passively. Figure 4.2 depicts the MTS in operation.
Straddle Carrier (SC) A vehicle able to drive over a container and has the capability of raising it 3 to 4 tiers high (see Figure 4.3). It is used to transport containers from the quayside to the stack, but can also be used as yard equipment or landside loading equipment. The Straddle Carrier can load and offload containers without the need of other handling equipment (active loading).
14 Container handling equipment
Figure 4.3: Two Straddle Carriers at a
storage yard (Hivemind, 2009).
Figure 4.4: A Shuttle Carrier (Port Strategy, 2012).
Figure 4.5: Automated Shuttle Carriers
at a stack (Port Strategy, 2013).
Figure 4.6: AGV’s at Hamburg Hafen
CTA (Terex, 2009).
Shuttle Carrier (ShC) Similar to the Straddle Carrier but is able to drive faster since containers can only be lifted 2 tiers high, making the vehicle less tall and thus lowering the center of gravity. The vehicle can load actively and is driven by an operator in a cabin. The Shuttle Carrier is depicted in Figure 4.4.
Automated Shuttle Carrier (AShC) This Shuttle Carrier is fully operated by a computer in order to circumvent the need for human operation. Sensors allow it to load automatically (active loading) when a central computer instructs it to do so. Figure 4.5 depicts the Automated Shuttle Carrier.
Automated Guided Vehicle (AGV) A single body vehicle that is able to operate without human intervention (see Figure 4.6). It serves a similar purpuse as a Tractor-Trailer Unit without its operator, being able to carry two TEU at a time. The AGV is normally loaded by other equipment (passive loading) before it can perform the horizontal transport.
Automated Lifting Vehicle (ALV) In some cases however, an AGV has the capa-bility of loading containers from a raised platform without the need for other equipment. In such a case, this is named an ALV. This vehicle has only partially active loading, since it can only load items from a raised platform, depicted in Figure 4.7. When containers are otherwise, it relies on other equipment to load it.
4.3 Yard handling equipment 15
Figure 4.7: Automated Lifting Vehicles
(Totaal-Trans, 2014).
4.3
Yard handling equipment
In order to use the area of a container yard more efficiently, some equipment is used to stack containers. This however means that shuffling becomes important when the desired container is at the bottom of the stack. Carlo et al. (2014), Vis and de Koster (2003) and Steenken et al. (2004) mention which types of equipment perform these operations. Reachstacker A vehicle with a telescopic arm that can lift containers to or from the stack (see Figure 4.8). Generally, the reachstacker loads and offloads TTU’s and MTS’s at the stack but transporting the container from the quay wall to the stack is also a possibility. This vehicle has active loading capabilities.
Empty Container Handler The container handler has similar capabilities to the Reach-stacker but contrarily to it, the arm is in a permanent vertical position, making it harder for this vehicle to drive into warehouses. The functionalities however remain the same, with an emphasis on the handling of empty containers. This vehicle is also able to load actively and can lift two empty container at a time, as can be seen in Figure 4.9.
Rubber-Tyred Gantry crane (RTGc) A yard crane that is placed on rubber tyres. The vehicle is not bound to a specific block, making its operation flexible (Petering, 2009). The main function of the crane is to transfer containers from a transport unit to the stack and vice versa. The crane is equipped with a spreader, allowing it to actively load (see Figure 4.10).
Rail-Mounted Gantry crane (RMGc) A yard crane that uses rails to travel along. This crane cannot move to a different block, since it is bound to its set of rails, which are usually not crossed by horizontal transport equipment. It serves the same purpose as the RTGc, to transfer containers from the horizontal equipment to the stack. As was discussed in subsection 3.2.2, the RMGc usually operates with
16 Container handling equipment
Figure 4.8: A Reachstacker (Totaal-Trans, 2011).
Figure 4.9: Empty Container Handler
(Wikipedia, 2010).
Figure 4.10: Rubber-Tyred Gantry crane (Kone Cranes, 2012a).
Figure 4.11: Rail-Mounted Gantry crane (Wikipedia, 2011).
transfer points at the end of the stack instead of a transfer lane which is typical for RTGc’s. The crane has active loading and a figure of the equipment is depicted in Figure 4.11.
Wide-Span Gantry crane (WSGc) Thoresen (2014) mentions one other type of gantry crane, the WSGc. This crane is wider than a regular RMGc, up to 80 meters, and has a cantilever of up to 40 meters (Figure 4.12). This crane is usually operated on inland intermodal container terminals for barges, rail or road transshipment, however there are instances where these are used manually or semi-automated on container yards.
Overhead Bridge crane (OHBc) The Overhead Bridge crane, Figure 4.13, is similar to the Rail-Mounted Gantry crane but the rails are placed on a structure above the container stack. This allows trucks to pass without interference from the tracks. The functionality is comparable to the RTGc and RMGc and incorporates self loading (active loading).
4.4 Equipment overview 17
Figure 4.12: A Wide-Span Gantry crane
with cantilever (Kone Cranes, 2012b). Figure 4.13: An Overhead Bridge crane
(Whiting Corp, 2007).
4.4
Equipment overview
After stating all the different equipment types, a summary is provided in Table 4.1. The information was based on Kalmar (2003) and summarized by Brinkmann (2011). Kemme (2012) supports this data with his own research. Additionally, the principle of loading is stated accompanied by the storage density, as particular yard handling equipment can lead to different amounts of container densities that are achieved in the storage area. Both Brinkmann (2011) and Kemme (2012) mention similar storage equipment. Saanen (2004) and Steenken et al. (2004) however, additionally mention storage on truck chassis.
Table 4.1: Summary of the functionality for each equipment type, as well as loading
capability (see Brinkmann (2011), p.25-39).
Transport Yard handling Loading Storage density
Tractor-Trailer Unit x - Passive 250 TEU/ha
Multi-Trailer System x - Passive
-Straddle Carrier x 1-over-3 Active 750 TEU/ha
Shuttle Carrier x 1-over-1 Active 250 TEU/ha
Automated Shuttle Carrier x 1-over-1 Active 250 TEU/ha
Automated Guided Vehicle x - Passive
-Automated Lifting Vehicle x - Active
-Reachstacker x 5 high Active 350-500 TEU/ha
Empty Container Handler x 5 high Active 350-500 TEU/ha
Rubber-Tyred Gantry crane - 1-over-7 Active 1000 TEU/ha Rail-Mounted Gantry crane - 1-over-7 Active 1000+ TEU/ha
Wide-Span Gantry crane - 1-over-7 Active 1000+ TEU/ha
Chapter 5
Generic terminal concepts
A condensed description of a typical container terminal is given in chapter 3. Brinkmann (2011) states that such a terminal is frequently between 600 and 800 meters wide, from quay to hinterland. The length of the quay wall depends on the berth capacity desired by the operators.
This chapter will elaborate on the combination of equipment types, related to the aspects from section 3.2. Each layout can be operated with a combination of the equipment (Wiese et al., 2009) discussed in chapter 4. The implementation of vehicles is discussed in section 5.1. Additionally, section 5.2 then discusses which terminal design would have preference over another according to several sources.
5.1
Equipment implementation
Several types of equipment are often combined with one another to allow for both the horizontal transport and the lifting of containers. This section introduces the combi-nations which are made frequently by terminal operators. For each of these, a short description, and if available the yard layout, is depicted. For the RMGc layout with unmanned vehicles, subsection 5.1.5, additional information was retrieved which related the size of the back-reach with the type of unmanned vehicle.
5.1.1 Reachstacker with Truck-Trailer Units
When an Ship-To-Shore crane (STSc) unloads a container from the ship, the container is placed on the trailer of the truck. Hereafter, the TTU transports the container to a storage block, where a Reachstacker places the container in the stack. This process
5.1 Equipment implementation 19
Figure 5.1: Straddle Carrier system in parallel position (see Kemme (2012), p.68).
is reversed when the ship is loaded. Similarly, the Reachstacker retrieves the container from the stack and places it on an outbound truck or vice versa. The storage capacity is about 350 TEU/ha for a stack of 3 tiers and 500 TEU/ha for 4 tiers high. Usually, the stack is 4 positions wide. When a container needs to be transported for a short distance, the Reachstacker does this by itself. Empty containers are handled by Empty Container Handlers, which can transport up to two containers at a time (Brinkmann, 2011; Kemme, 2012).
5.1.2 Straddle Carrier system
In the Straddle Carrier system, the storage yard is operated with the use of Straddle Carriers. Storage can be achieved by driving over a lane with the Straddle Carrier and discharging the container into the stack. The orientation of the lanes is arbitrary. When this option is used, it is very likely that transport between the quayside and stack as well as the transport from stack to truck or train handover area will occur with the use of Straddle Carriers (Kemme, 2012). Access roads are placed parallel and perpendicular to a group of lanes, as can be seen in Figure 5.1.
Depending on the type of Carrier, the stack can be two or three tiers high. A Straddle Carrier must be able to retrieve a container from the center of the lane and therefore has the ability to lift three to four container positions high. A major advantage of this
20 Generic terminal concepts
system is that the Straddle Carrier can load and unload the container by itself, as well as stacking the containers (Brinkmann, 2011).
In Australia, at the Brisbane AutoStrad Terminal, the Straddle Carrier system is au-tomated and both horizontal transport as well as stacking is done with the Kalmar AutoStrad system, which can stack 1-over-2 high.
5.1.3 Rubber-Tyred Gantry crane with Truck-Trailer Units
Similar to the Reachstacker and TTU system, however transfer by a Reachstacker is now substituted with transfer by RTGc. Transport often happens with the use of tractor-trailer units, but there are occurrences where MTS’s are used (Kemme, 2012).
Because of heavy wheel loads, heavy concrete paving is required in the storage yard. As was mentioned in Table 4.1, an RTGc has a maximum stacking height of 1-over-7, thereby increasing the storage density to 1000 TEU/ha. Blocks are usually 5 to 8 containers wide (Brinkmann, 2011) and can be oriented both parallel or perpendicular, depending on the terminal operators’ preferences. Both Brinkmann (2011) and Kemme (2012) do not mention the possibility of having RTGc’s in a perpendicular position, however research from Wiese et al. (2009) indicates that this can indeed be an option. Out of the 54 terminals that were investigated by Wiese et al. (2009), two terminals using RTGc’s had a perpendicular layout and three terminals use a combination of both orientations, similar to what is shown in Port of Los Angeles (2014).
The layout permits landside traffic, such as trucks (XT’s), to drive into the storage yard (see Figure 3.3). This introduces the possibility of interference between waterside and landside traffic. Because of this, the layout has very little potential for automation, since there is a need for safety and there is interaction with non-automated traffic (Kemme, 2012).
5.1.4 Rail-Mounted Gantry crane with manned vehicles
The RMGc system with manned vehicles acts equally to the RTGc system, but the transfer lane is handled by the cranes cantilever. The terminal can also have a parallel or perpendicular orientation. Instead of rubber tyres, rail tracks are used. These tracks require more initial investment costs and do not allow cranes to switch from blocks. This has negative effects on the capacity of the terminal when a crane fails.
The Rail-Mounted Gantry crane has the ability to stack 1-over-7. However, because the RMGc has a wider span than the RTGc (12 containers wide), it allows for more than 1000 TEU/ha. Brinkmann (2011) states that the RMGc is easier to automate than the RTGc.
Kemme (2012) suggests several different uses with RMGc’s, based on Saanen and Valken-goed (2005) and Dorndorf and Schneider (2010). The first is a single-crane system.
5.1 Equipment implementation 21
Figure 5.2: Cross section of a typical automated terminal quay (see Ranau (2011), p.184).
Herein, an entire stack is operated with one crane. The second is a system with two RMGc’s in twin formation, meaning that both RMGc’s use the same set of rail tracks. This causes interference between the two machines which can be resolved by using the double formation. Herein, two RMGc’s are able to pass each other because one is larger than the other and uses a different set of rails. The last system uses three Rail-Mounted Gantry cranes, with two cranes on the same set of tracks, and one larger crane on a different set of tracks. This system has an increased handling capacity, but also requires more space and has a higher number of interferences, making the scheduling more diffi-cult. Container Terminal Buchardkai in Hamburg has implemented this idea to double the terminal throughput capacity (Dorndorf and Schneider, 2010).
5.1.5 Rail-Mounted Gantry crane with unmanned vehicles
Instead of requiring an extra row for vehicles to complete the handover, RMGc system can perform the handover at the begin or the end of the stack. This allows for the separation of landside and waterside traffic, increasing the potential for automation (Brinkmann, 2011; Kemme, 2012). Horizontal transportation at the quayside of the terminal is performed either by ShC’s, AShC’s, AGV’s or ALV’s. Landside trucks enter the terminal via the gate facilities and await handling by the RMGc.
Figure 5.2 projects the cross section of the quay of an automated terminal. The quay is separated from the terminal to ensure a safe working environment. According to Ranau (2011), there are several operations which need to take place in the terminal apron:
• Twistlock handling
• Handling of out of gauge cargo
• Quayside and vessel access for services • Preparation of break bulk cargo
22 Generic terminal concepts
Figure 5.3: Dimensions of a perpendicular layout AGV or ALV system (see Ranau (2011),
p.190).
The transfer of standard containers to and from the yard is performed in the backreach of the STS crane. This will prevent mixing of automated and manned traffic. Also, automated vehicles between STSc legs would result in tunnel effect and result in lower productivity of horizontal transport units. A total of 35 meters needs to be reserved.
Transfer by AGV or ALV
Several aspects influence the space requirement of an automated container terminal. For safety reasons, 2 meters are required between the rails of the STSc and the first drive lane. A drive lane in the backreach of an STSc requires about 4 meters in width, taking the turning radius and length of the vehicle into account. The holding area, used for intermediate storage and parking of transport units, needs a length of 28 meters for AGV’s in order to make the 90 degrees turn from the drive lanes. In an interview (Appendix A), it is mentioned that the most logical place for the holding area is between the two driveways, since this area is unoccupied due to the 180 degrees turn that has to be made by AGV’s, ALV’s, ShC’s and AShC’s at the end of the quay. Furthermore, drive lanes close to the storage yard require 4 meters, with the lane closest to the holding area requiring 5 meters. An additional 8 meters is required for turning into the ASc block handover area. Finally, the handover area for the ASc is 20 meters. This results in a total of 96 meters. The decomposition can be viewed in Figure 5.3 (Ranau, 2011). Examples of such container terminals are present in Rotterdam, at the APM Maasvlakte II Terminal and the Hamburg Container Terminal Altenwerder. At Hamburg-Altenwerder, six main driveways are used with a quay length of 1400m (HHLA Container Terminal
5.2 Influencing factors 23
Figure 5.4: Dimensions of a perpendicular ShC or AShC system (see Ranau (2011), p.191).
Altenwerder GmbH, 2010). The Euromax Terminal, operated by Europe Container Ter-minals is similar, but the Delta Terminal of ECT has drive lanes between the STSc legs. This conflicts with the theory by Ranau (2011).
Transfer by ShC or AShC
The length of an ShC or AShC is 11.3 meters and it is 4.9 meters wide. However, the largest loading unit that has to be accounted for is 13.72 meters in length. Therefore the drive lanes should be 6.4 meters wide each. Although the lanes are wider, the length of the holding bay is only 18.5 meters. This allows for the decoupling of the STSc and ASc operation. The main driveways require a space of 6.4 to 7.4 meters wide and an additional 5 meters between the last driveway and handover area. The ShC or AShC is able to carry containers 1-over-1, this is used to place 4 TEU in the ASc handover area. The extra length also gives the possibility to hold a broken ASc in the first slot area, while a second crane is still able to access the remaining 2 TEU.
A short overview is depicted in Figure 5.4. The TraPac Terminal at the Port of Los Angeles intends to use this system, but is still testing the system for operation.
5.2
Influencing factors
In a publication, Wiese et al. (2011) discus which of the mentioned layouts would receive preference from terminal operators. A comparison by Vis (2006a) between the Straddle Carrier system and ASc’s for container storage concludes that with a row of six con-tainers, the ASc system usually outperforms the SC system. However, when the span
24 Generic terminal concepts
is increased up to nine containers, the performance of the SC then matches that of the ASc.
The paper by Liu et al. (2004) also adopts simulation to make a comparison between manual and automated terminals, for parallel as well as perpendicular terminal layouts. The validated model does not account for transshipment of containers, only ship load-ing and unloadload-ing. It is concluded that the terminal throughput can be increased by adopting AGV’s instead of manned vehicles. Simulation of AGV’s on a perpendicular layout shows that there is a higher throughput as compared to the parallel layout option. Petering (2008) shows with a model that parallel layouts are superior to perpendicular layouts. In specific cases however, perpendicular layouts can outperform its counterpart. By means of a simulation, Yang et al. (2004) conclude that AGV’s require longer waiting times than AShC’s as the AGV’s have to wait until they are loaded or unloaded. The simulation includes a vehicle traffic model in which roads are divided into zones. The zones only allow one vehicle to enter at a time. The simulation tests whether centralized or distributed control affects the results, which it does not. And when the speed of both vehicles is taken equal, the AShC requires less active units.
A method for determining the layout of container terminal storage yards has been pro-posed in Kim et al. (2008). The paper derives formulas for expected travel distance and the number of re-handles. In these calculations, the landside gate facility is ac-counted for, so a transshipment terminal can be mimicked. The researchers come to the conclusion that when the total costs are calculated, the parallel layout is preferred. Wiese et al. (2011) come to the conclusion that based on these papers, no superior orientation is observed and that the decision depends on a number of different factors. This statement is confirmed by M. Coeveld in Appendix A with commonly occurring factors:
Geometry of the available land The availability of land and its geometry inherently determine the size and options for the container terminal layout.
Transshipment ratio Whether a container terminal transships between different ves-sels or is used as a import/export terminal has influence over the orientation of the layout. A parallel layout is used mainly for vessel transshipment since accessibility to containers is better and a higher throughput can thus be obtained. The perpen-dicular layout is typically used for import/export terminals, where the quayside and landside can be separated which achieves a higher throughput for this type of terminal.
Investment and operational cost The availability of capital affects which equipment can and will be purchased whereas operational costs depend mainly on the location of the container terminal, as labour costs can have a large impact.
Chapter 6
Vehicle Routing
There are several problems which are typical for the control of vehicle fleets on container terminals. These problems can consist of the following three subjects: scheduling, dis-patching and routing. Scheduling mainly concerns the matching of a transport request with a time into a job, whilst dispatching assigns the job to a vehicle. It is stated by Adriaansen (2011) that the routing of vehicles is aimed at finding good paths for vehicles that are dispatched. Determining a path can be subject to various objectives, such as minimizing the travel distance or minimizing the interactions with other vehicles. These aspects can be influenced by several factors. This is the physical routing of vehicles, which Bae et al. (2008) mention as route creation. Opposing the route creation is the travel scheduling, which in this report is defined as logistic routing problems.
Multiple research studies have been done in the past on the routing of vehicles. Nishimura et al. (2009) shows the importance of this topic, by stating that quay cranes should not stop their operation and thus routing of horizontal transport equipment becomes very important. A literature survey on routing is performed by Steenken et al. (2004), Stahlbock and Voß (2008) and Vis (2006b). Pillac et al. (2013) have reviewed dynamic routing problems whilst Montoya-Torres et al. (2015) have solely focussed on vehicle routing problems with multiple depots.
This chapter will first introduce the aspects that are important for the routing of ve-hicles in section 6.1. Hereafter, the three dominant routing methods are elaborated in section 6.2. To finalize this chapter, articles are summarized according to these methods in section 6.3.
26 Vehicle Routing
6.1
Aspects of vehicle routing
In order to assess the different publications that are published, several aspects that are of importance for both the physical and logistic routing of vehicles on container terminals will be reviewed. This section intends to do so with the 3-Level-Model discussed in section 3.1. A significant amount of information is obtained from Kemme (2012), whilst Appendix A and Steenken et al. (2004) provide some additional information on the aspects as well.
• Operational measures and decisions
Cycling mode A typical container terminal with automated vehicles distinguishes the single-cycle and dual-cycle method to load and unload containers. In single-cycle mode, the vehicles serve only one crane and according to that cranes cycle, the vehicle either provides a container that will be loaded onto the ship or takes a discharged container from the ship to the storage yard. The dual-cycle mode has vehicles serving quay cranes for simultaneous loading and unloading of vessels, wherein the amount of empty rides is significantly reduced.
Door correction move Most containers only have a set of doors at one end of the unit. As the storage yard typically does not orient the doors in one direction, a door correction move has to be performed when loading the ship, such that all doors are facing a particular way. The route thus has to incorporate a door correction move when necessary.
Direction of driving On current automated container terminals, a certain direc-tion of driving is applied, which can either be clockwise or counter-clockwise. Depending on the direction of the container doors, one direction will have a lower amount of door correction moves. This depends on the way that the ship is oriented and the way containers in the stack are oriented.
Vehicle location Where dispatched vehicles are in respect to their destination is of great influence on the route. A vehicle closer to the pick-up point is preferred but not always available. It is therefore important to position vehi-cles which have no jobs assigned properly, so that the average distance to the pick-up is minimized. However, these empty vehicle movements should not cause extra congestion.
Traffic The routing algorithm has to prevent deadlocks and livelocks from hap-pening on the container terminal. Similarly, routing can prevent congestion or collisions when vehicles are routed to other paths as opposed to the con-gested paths. As is mentioned in Strategy, the amount of interference of vehicles can also have an impact on the routing and is sometimes used as a strategy on its own.
6.1 Aspects of vehicle routing 27
Breakdowns A vehicle in operation will occasionally break down, causing delays for other vehicles and locking in its current cargo. If a driveway is blocked, other vehicles can be rerouted to reduce the delays. Mending or towing of the broken vehicle can be difficult, especially on automated container terminals, as access to the automated area is often restricted.
Exception handling It sometimes happens that an exception occurs, for exam-ple the arrival of a container at the last possible moment or out of gauge cargo. This then means that part of the stowage plan as well as the active jobs need to adjusted.
Travel predictability An uncertainty in travel time can be caused by traffic density and several other factors such as breakdowns and interference from exception handling. This uncertainty directly influences the optimal schedule and with it, the optimal route for vehicles. Reducing this stochastic invariance may benefit planning and routing algorithms.
Loading As is discussed in chapter 4, the manner of loading is of importance to the vehicle routing. Active loading vehicles are not dependant on other equipment to load a container. Passive loading vehicles however are and need to wait for other equipment to be loaded, thereby affecting time and route. Quay operations As was seen with the door correction move, the stowage plan
and the crane loading strategy matter for the routing of vehicles. The se-quencing of jobs then also affects the routing of vehicles, as is argued by Steenken et al. (2004).
Yard operations Similarly to the quay operations, yard operations and storage plans influence routing of vehicles on the yard side of the terminal.
• Tactical measures and decisions
System architecture A factor which ties into both communication and compu-tational power is the control architecture. By using either centralized control or distributed control for the vehicles, different amounts of data transmission and centralized or decentralized computing power are required. This does not inherently change the routing of a vehicle, but does influence the capability of calculating the optimal solution within a certain time period and therefore affects the routing.
Computational power One aspect that highly influences the routing of vehicles is the amount of computing power that is required to perform calculations timely. As unexpected events may occur, routes need to be adapted quickly. Algorithms nowadays tend to get more complex as different functions and methods are added to it. To accomplish this in a relatively short calculation time, either a powerful computer is needed, or a simpler algorithm needs to be used.
Communication Based on which communication system conducts information between the vehicle and computing system, a specific amount of data can be
28 Vehicle Routing
transmitted per time unit. The data can contain information on the vehicles state and instructions about to where it should be headed. It is important that the data is less than the system is capable of transmitting and receiving, as incomplete data will result is failure of the routing system.
Pooling Equipment operating at a container terminal can be dedicated to one quay crane or all vehicles can be combined into a pool which provides a vehicle to a quay crane when one is requested. This has some effect on routing. An important difference between manned and unmanned routing is that unmanned vehicles will always be pooled and manned vehicles commonly operate with a fixed allocation principle (Steenken et al., 2004).
Safety It can be argued whether safety is a tactical or operational measure. Leg-islation however is a factor which does not change on a day-to-day basis and therefore the safety measures on a terminal do not. The measures and decisions on tactical level are implemented to secure cargo, equipment and personnel. How this affects routes can be in different ways, for example cer-tain zones need to be avoided for safety reasons, or vehicles are bound to a certain speed and acceleration. Distance from objects or other vehicles can also be a factor which needs to be accounted for.
Zoning The driveways for automated horizontal transport vehicles are often di-vided into zones. Depending on the strategy and imposed safety margins, typically one vehicle is allowed per zone. Several algorithms do allow multi-ple vehicles to enter a zone if collisions can be avoided. Naturally, this affects the routing of vehicles. Free ranging AGV’s even allow for an absence of zones, close to how manned vehicles operate.
• Strategic measures and decisions
Layout The position and orientation of the stack, the topology and unloading point matters for the optimal route. chapter 5 is dedicated to explaining the different options that exist to design the layout of container terminals. Strategy There are several different strategies available for the routing of
vehi-cles. Equipment can for example be routed on basis of shortest travelling time, shortest travelled distance or lowest cost. Research has also provided algorithms which aim at minimizing the interference between different vehi-cles in order to get a higher throughput. This changes the route significantly as congested areas are avoided. Further details on partitioning of strategies is presented in section 6.2.
6.2
Routing methods
According to Vis (2006b), there are two types of routing. These are static and dynamic routing methods. In Duinkerken et al. (2012) is distinguished between fixed topology and
