Theoretical Framework (Module) for Short-Sea Shipping System Evaluation

Abstract

Short-sea shipping, abbreviated SSS, is the transportation of goods by sea over relatively short distances, in contrast to intercontinental ocean and deep-sea shipping. Short-sea shipping (SSS) is important for cargo transportation in some regions of the world with many ports and well-developed liner shipping. The development and improvement of SSS systems is an important scientific and practical task. This article presents theoretical and experimental results of the development and optimization of SSS. A methodology for connecting and evaluating SSS and other transport chains was developed and tested by experimental studies, with the help of which it is possible to assess the efficiency of SSS and other transport chains, e.g., in terms of economy, freight transportation time, and environmental impact. The developed SSS methodology includes sea and land transport corridors, their assessment, and possible ways of optimizing transport chains using a comparative method and can be applied to various transport and logistics chains. The basis for the development and verification of the SSS methodology was the theoretical and experimental results of real short-sea shipping operations. The use of a comparative method based on which transport and logistics chains are assessed allows one to search for the most optimal SSS routes and possible factors that allow optimizing transportation costs and reducing transportation time and environmental impact.

1. Introduction

Short-sea shipping, abbreviated as SSS, is the maritime transport of goods over relatively short distances, as opposed to intercontinental cross-ocean deep-sea shipping. In the context of European Union (EU) transport statistics, it is defined as the maritime transport of goods between ports in the EU (sometimes also including candidate countries and EFTA countries), on one hand, and between ports situated in geographical Europe, on the Mediterranean, and on the Black Sea, on the other hand [1,2].

The development of short-sea shipping affects the functioning of supply chains. Therefore, SSS and logistics operators should carefully analyze the conditions of their operations and their place in these chains, as well as properly organize transportation and service provision processes, taking into account possible disruptions [3,4,5].

Ports play an important role in supply chains. A wide range of specific services are provided through an SSS system. Services can be provided by a single SSS company or by several transport companies on a commercial basis, but in some cases, a single SSS operator can manage the entire process. In addition, the SSS system should have vessels and equipment required to provide specific services [3,4,5].

Short-sea shipping (SSS) is oriented towards shipping between EU ports and is mainly concerned with legal issues such as decreasing the number of documents and procedures.

Nowadays, there are many ports and fixed shipping lines between ports operating in various countries that offer transport services to customers. SSS is one of the transportation systems that allows one to optimize transportation processes between ports. In addition, the SSS system can offer other additional services such as cargo handling services, optimization of vehicle utilization and storage space, etc. [4,5].

In some countries, there are limitations to creating SSS lines, but those countries possess many small and medium-sized ports located in different places, and it is difficult or even impossible to integrate them physically. The relevance and novelty of the article is an attempt to theoretically substantiate and practically verify the possibility of combining the logistics functions of port located in different places by creating SSS, in which representatives of small and medium-sized ports “scattered” in specific regions would participate in joint activities to minimize transportation costs and provide better services to clients.

The SSS concept is intended for ports, shipping companies, and other transport service providers to make sustainable decisions regarding optimal cargo transportation between ports and other locations where maritime transport is or may be involved in transport processes [4,5,6].

It should be noted that large companies have more opportunities related to the organization of cargo transportation using SSS, including the optimization of transport processes using SSS and other types of transport, for example, rail or road transport. In the case of the need to transport relatively small cargo lots, the SSS system is important, since the combination of small consignments of goods with other consignees’ consignments allows for the optimization of transportation processes [3,5].

The aim of the article is to theoretically substantiate the possibilities of developing a short-sea shipping (SSS) system by combining the activities of existing and developing inter-port shipping lines and terminals into a single entity in order to reduce the cost of transportation services and the delivery time of goods, as well as to create a comprehensive range of transportation services needed by customers.

Modern supply chains operate using an SSS system that includes shipping lines, intermodal terminals located in seaports and other locations, and the linear infrastructure of maritime transport. This infrastructure can be dispersed, so it is difficult to directly (mechanically) organize SSS processes. Therefore, taking into account the needs of transport companies and customers, special structures (compounds) should be created to manage freight transportation services on the basis of agreements [7].

In global transportation networks, seaports are traditionally defined as the interface between sea and land transport. At the same time, seaports in cargo transportation systems take into account the fact that modern ports are spatial, logistical, financial, and information centers. Information and communication technologies have radically separated information from the flow of physical goods.

Using SSS, it becomes possible to create sustainable cargo transportation systems by various modes of transport. The main goal of the article and the novelty of the research are related to the complex comparative assessment of cargo transportation, which is very important for the selection of sustainable cargo transportation methods.

The novelty and innovation of the article is based on the study and assessment of the elements of the short-sea shipping system and the creation of a comparative index between short-sea shipping and other transport corridors, designed to assess and determine optimal and sustainable freight transportation conditions, taking into account the cost of freight transportation, time, cargo rerouting, energy consumption and emissions generated by transporting specific types and quantities of cargo, and practical applicability.

2. SSS Situation and Analysis of the Literature

Short-sea shipping is an important part of the transport system and is mostly focused on cargo transportation between ports, with the aim of optimizing the legal framework between countries and minimizing the optimization of ship and cargo procedures in ports [1]. Due to the fact that there are no economic borders in the European Union, there is an opportunity to minimize the number of documents and procedures for vehicles and cargo transported between different places in the EU [1,2,3]. The International Maritime Organization (IMO) Convention on Procedures provides for the main ship and cargo documents [8], and the legal hurdles of SSS can be resolved using these conventions. At the same time, using different modes of transport allows one to search for optimal solutions depending on the conditions of cargo transportation and various restrictions [9].

In most cases, cargo is transported between the main regions of the world economy by ocean routes between the main ports (hubs), and then feeder or tramp transportation is most often used between the main and final or so-called feeder ports, using the recognized legal basis of the FAL Convention [8]. It is also necessary to note that some countries have enacted additional legal acts, which sometimes differ significantly from the system adopted by the FAL Convention; therefore, one of the main goals of the SSS system is to unify different legal bases for cargo transportation of countries, regardless of whether there are economic borders between the ports of cargo transportation or not, as, for example, in the EU area [2,9]. The SSS system is one of the essential ways to optimize cargo transportation and achieve sustainability of transportation [3].

SSS is analyzed in various sources which study various elements of the transport chain to adapt them to the development of new transport systems [9,10]. The main goal of transport systems, including SSS, is fast, safe delivery of goods between ports, while optimizing transportation costs [11]. Fast delivery of goods between ports is associated with the ability to use the advantages of linear shipping if there are shipping lines between ports [12,13,14]. If there are no shipping lines between specific ports, then it is very important to compare the possibilities of transporting goods by different modes of transport, using tramp shipping by ships and other transport systems [14].

In the SSS system, ports occupy a special place, and loading and other logistics operations are carried out there to minimize the time of ship-loading operations, since with relatively short transportation distances, the passage of ships between ports takes relatively little time, and in some cases, loading operations in ports are carried out in close proximity to ship navigation; i.e., the efficiency of transportation by ships decreases. Optimization of port operations by minimizing the time of ship processing in ports is one of the essential ways to increase the efficiency of transport and logistics chains [2,4,7,14].

By minimizing the handling of ship formalities in ports through using the capabilities of the SSS system, conditions arise to better concentrate on cargo assembly in port terminals, similar to logistics centers [5,7], since the SSS system is associated with linear shipping, i.e., the creation and adherence to specific ship sailing schedules and the publication of basic transportation prices [11].

By optimizing transportation processes based on SSS, energy costs for transporting the same amount of cargo are reduced, and environmental impact is reduced [15,16,17,18]. Short-sea shipping has a significant impact on various regions of the world by improving cargo and passenger service [13,19,20,21].

Short-sea shipping research initiates new shipping solutions such as the development of autonomous shipping between specific ports, especially where shipping intensification is not high; the search for and development of new cargo processing systems at terminals; and broader digitalization capabilities of shipping and ports [22,23].

Due to the fact that the SSS system is oriented towards the transportation of goods between ports—and not between shippers and consignees as the Motorways of the Sea (MoS) system is [24]—and, therefore, also towards transportation from shippers to ports and from ports to consignees [25,26], these parts of the transport and logistics chains must be developed in parallel with SSS.

Based on an analysis of oceanic, tramp, and short-sea shipping and of the literature, it can be stated that short-sea shipping is an important part of the overall sustainable transport system [14,27,28], the integration and complex assessment and optimization of which with other modes of transport substantiates the importance of similar scientific research and the necessity of practical application.

3. Theoretical Basis of the Evaluation of Short-Sea Shipping Processes

3.1. Steps of SSS Research Methodology

The following stages of the SSS system research methodology were applied to conduct the study (Figure 1). After conducting a literature review, a mathematical model of the SSS system was developed.

Theoretical calculations of cargo transportation using SSS and other transportation methods were performed. The dispersion and maximum distribution methods [23] were used to design the SSS system, using data obtained during experiments. The maximum distribution method could be applied when at least five measurements were made.

SSS, which includes cargo transportation between ports and the possibility of transshipment, can be graphically represented in the following diagram (Figure 2).

A case study was conducted to verify the theoretical calculations and practical application of the presented methodology. Based on the established assumptions, cargo transportation simulations using SSS and the road transport systems were performed. Experiments were performed based on cargo transportation data from shipping lines and road transportation between selected countries.

3.2. Mathematical SSS System Model

The main conditions for developing an SSS system based on existing shipping lines and ports are as follows:

-

Identification of existing shipping lines and ports, as well as cargo transportation services;

-

Identification of locations of cargo consignors and consignees and the need for services;

-

Identification of possible cooperation schemes, assessment of technical capabilities in order to find the best solutions for the analyzed cases, and assessment of possible alternative transportation services.

The following criteria are possible for assessing possible cooperation solutions:

-

Time of provision of the SSS system or other modes of transport service;

-

Price of the SSS system or other modes of transport service;

-

Possibility of redirecting goods to another service provider when performing transportation services in ports or other locations;

-

Energy demand for providing the SSS system or other modes of transport services and environmental impact.

When assessing the main SSS factors influencing the sustainability of freight transport and the ability to compare different modes of transport, the created comparative index is presented as follows:

$$K_L=f(P_L, T_L, D_L, E_L,A_L\dots ),$$

(1)

where $P_L$ denotes the transportation services’ price function using SSS or other transport systems; $T_L$ denotes the time function of transportation between two ports; $D_L$ denotes the costs function of goods readdressing and distribution in ports or other locations; $E_L$ denotes the energy demand function, including emissions; and $A_L$ denotes additional payments (costs) for environmental impact (emissions).

By applying the comparative index of SSS and other transport system services, it is possible to comprehensively assess the possible main transport services, to transport goods using the SSS system, and to use direct delivery of goods by other modes of transport (taking into account price, time, aspects of distribution and routing of goods, energy consumption, environmental aspects), which is very important when it is necessary to optimally use transport means, using goods from different senders and recipients, and deliver them to final recipients. Using the SSS system and direct delivery of goods, for example, by road transport, it is possible to find the most optimal solutions.

Price function can be expressed using SSS and/or other transportation system services’ lump sum prices (prices of different activities within transportation services in different ports or other terminals) and the number of used ports or intermodal facilities, as is presented by Equation (2), which must include transportation prices (tariffs) by various modes of transport, quantities or units of cargo transported, and weight coefficients for transportation by different modes of transport:

$$P_L={\displaystyle \frac{1}{{\eta }_P}}(k_P{P}_S{N}_T+k_R{P}_R{N}_T+k_T{P}_T{N}_T+\cdots )$$

(2)

where ${\eta }_P$ denotes the correlation coefficient for a similar process (this could be between 0.98 and 1.0 (in case of one transport mode, correlation coefficient will be 1.0—typical for transport systems)); $k_P$ denotes the discount coefficient, which depends on the quantity of transportation cargo or units; $P_S$ denotes the price (tariff) of sea transportation for one cargo or transport unit; $N_T$ denotes the number of cargo or units transported by the SSS system; $k_R$ denotes the discount coefficient, which depends of the quantity of goods or units transported; $P_R$ denotes the price (tariff) of road transportation for one cargo unit; $k_T$ denotes the discount coefficient, which depends on the quantity of the cargo or units transported by railways; $P_T$ denotes the price (tariff) of railway transportation for one cargo unit; and +… denotes other possible transportation systems’ price elements, like payments for emissions trading and so on, as well as prices of services performed using additional ports or terminals.

The price of transportation by ship, in general, of one cargo unit or of a ship’s party, for example by RORO ship, ($P_S$), can be calculated as follows [10,11]:

$$P_{OTHC}+P_{BAF}+P_{CAF}+P_{ISPS}+P_{WRS}+P_{CONG}+P_{PORT}+P_{THC}+P_{DOC}+P_{IMP/EXP}+P_{S/P}{+P}_{RF}=P_S,$$

(3)

where $P_{OTHC}$ denotes the sea freight factor; $P_{BAF}$ denotes the bunker adjustment factor; $P_{CAF}$ denotes the currency correction factor; $P_{ISPS}$ denotes the International Ship and Port Facility Security factor; $P_{WRS}$ denotes the war risk factor; $P_{CONG}$ denotes the factor for the cost of transshipment in ports; $P_{PORT}$ denotes the port dues factor; $P_{THC}$ denotes the terminal handling fee factor; $P_{DOC}$ denotes the factor for the fee for the preparation of document; $P_{IMP/EXP}$ denotes the export/import tax factor; $P_{S/P}$ denotes the Panama/Suez Canal fee factor; and $P_{RF}$ denotes the fee for connecting the referring container and other factors.

In the case of SSS in different regions of the world [16,18] where transportation can be carried out mainly over relatively short distances, Formula (3) can be applied as follows:

$$P_S=P_{OTHC}+P_{BAF}+P_{CAF}+P_{ISPS}+P_{CONG}+P_{PORT}+P_{THC}+P_{DOC}+P_{IMP/EXP}+P_{RF}.$$

(4)

Using the SSS system, shipping lines usually set a total (lump sum) price ($P_L$) for the transportation of cargo units and a system of possible discounts, into which direct terminal service and transportation vessel prices are entered (like ticket prices from entry into a departure port terminal and departure from an arrival port terminal); then, Formula (4) can be written as follows:

$$P_S=P_L.$$

(5)

The transportation services time function ($T_L$), using the SSS sytem or other transport modes for a specific quantity of cargo or units, including freight transport distances, vehicle speeds, and weight coefficients of transport modes, can be expressed as follows (Equation (6)):

$$T_L={\displaystyle \frac{1}{{\eta }_T}}(k_{ST}{\displaystyle \frac{S_S}{v_S}}{N}_T+k_{RT}{\displaystyle \frac{S_R}{v_R}}{N}_T+k_{TT}{\displaystyle \frac{S_T}{v_T}}{N}_T+\cdots ),$$

(6)

where ${\eta }_T$ is the correlation coefficient in case of similarities between transport modes (this could be between 0.95 and 1.0 (in the case where one transport mode is used, this coefficient will be one)); $k_{ST}$ is the time function coefficient for SSS transportation (which depends on weather conditions, waiting to enter the port, and so on; for liner shipping, this depends on the probability fluctuation from the planned time table); $S_S$ is the sea distance between SSS ports; $v_S$ is the ship’s commercial speed; $k_{RT}$ is the time function coefficient for road transportation, which depends on traffic and road conditions and mainly depends on the probability fluctuation from the planned time table; $S_R$ is the distance by roads between ports or other locations; $v_R$ is the average speed of road transport for the freight, including mandatory stops for drivers to refresh and so on; $k_{TT}$ is the time function coefficient for railway transportation, which depends on the required stops during crossing countries’ borders and so on and mainly depends on the probability fluctuation from the planned time table; $S_T$ is the distance by railway between ports or other locations; $v_T$ is the train’s commercial speed; and $+\cdots$ is other possible time elements such as the waiting time of the ship upon entering the port, as well as the time required for unloading and loading the ship or other means of transport, and any other possible additional time.

The cost function ($D_L$) of storing, redirecting, and distributing goods in ports or other locations for a specific quantity of cargo units can be expressed, taking into account the periodicity of SSS transportation and the possibility of promptly redistributing cargo (similar to airports), as follows (Equation (7)):

$$D_L={\displaystyle \frac{1}{{\eta }_D}}(k_{SD}{N}_T^{\prime }+k_{RD}{N}_T^{\prime }+k_{TD}{N}_T^{\prime }+\cdots ),$$

(7)

where ${\eta }_D$ is the correlation coefficient in cases where there are similarities between cargo or goods distribution in different transport modes (this could be between 0.97 and 1.0 (in cases where one transport mode is used, this coefficient will be one)); $k_{SD}$ is the cost function coefficient, which depends on the operations that should be carried out in ports or terminals and on SSS possibilities and transportation procedures; $N_T^{\prime }$ is the quantities of the cargo or number of transport units for which additional operations in ports or terminals are required; $k_{RD}$ is the cost function coefficient, which depends on the operations which should be carried out during transportation by roads (in the case of overweight freight, additional leasing, etc.); $k_{TD}$ is the cost function coefficient, which depends on the operations which should be carried out during transportation by railways (in case of additional leasing before entering into railway ferries, etc.); and $+\cdots$ refers to other possible cost elements such as special requirements for the placement and securing of dangerous goods in vehicles, etc.

For the entire load or a unit of it, for example, a unit of a freight vehicle, the energy demand function, which includes the average power used by the main engines of the transport modes, the relative fuel consumption, the types of fuel used, for example, diesel fuel, LNG, and others, ($E_L$) can be expressed as follows (Equation (8)):

$$E_L={\displaystyle \frac{1}{{\eta }_E}}(q_{fS}^{\prime }{N}_{WS}{\displaystyle \frac{S_S}{v_S}}{N}_T+q_{fR}^{\prime }{N}_{WR}{\displaystyle \frac{S_R}{v_R}}{N}_T+q_{fT}^{\prime }{N}_{WT}{\displaystyle \frac{S_T}{v_T}}{N}_T+\cdots ),$$

(8)

where ${\eta }_E$ is the correlation coefficient in case of similarities between transport modes’ fuel consumption (this could be between 0.97 and 1.0 (in the case where one transport mode is used, this coefficient will be one)); $q_{fS}^{\prime }$ is the relative fuel consumption of the ship’s engine, which is between 0.15 and 0.20 kg/kWh; $N_{WS}$ is the ship engine’s average power during sailing between SSS ports; $q_{fR}^{\prime }$ is the relative fuel consumption of the road transport engine, which is between 0.12 and 0.18 kg/kWh; $N_{WR}$ is the road transport unit’s average power during a voyage between SSS ports or other locations; $q_{fT}^{\prime }$ is the relative fuel consumption of the road transport engine, which is between 0.15 and 0.18 kg/kWh; $N_{WT}$ is the railway transport unit’s average power during a voyage between SSS ports or other locations; and $+\cdots$ is other possible elements, like energy demand during transportation and atypical transportation, for example, special services transportation of dangerous goods, etc.

For the transportation of cargo or its unit quantities using the SSS system and other modes of transport, the emissions generated by a specific mode of transport (carbon dioxide, carbon monoxide, sulfur oxides, nitrogen oxides, and particulate matter) depend on the amount of fuel consumed, the average power of the vehicle engines, and their operating time; ($A_L$) can be expressed as follows (Equation (9)) [12,13,19]:

$$A_L={\displaystyle \frac{1}{{\eta }_A}}(∆{\mathrm{C}\mathrm{O}}_2{q}_f+∆{\mathrm{S}\mathrm{O}}_x{q}_f+∆\mathrm{C}\mathrm{O}{\mathrm{N}}_{W}t+∆{\mathrm{N}\mathrm{O}}_x{N}_{W}t+∆\mathrm{P}\mathrm{M}{\mathrm{N}}_{W}t),$$

(9)

where ${\eta }_A$ is the correlation coefficient in case of similarities between emissions generated (including fuel consumption, as well as the average engine power of the transport mode (this could be between 0.95 and 1.0 (in the case where one type of emission is calculated, this coefficient will be one))); $∆{\mathrm{C}\mathrm{O}}_2 \mathrm{i}\mathrm{s} \mathrm{t}\mathrm{h}\mathrm{e} {\mathrm{C}\mathrm{O}}_2$ emission generation coefficient, which depends on the type of fuel (for example, for diesel fuel, on average, this coefficient is 3.2; for LNG fuel, it is 2.7); $q_f$ is the fuel quantity used during the voyage; $∆{\mathrm{S}\mathrm{O}}_x \mathrm{i}\mathrm{s} \mathrm{t}\mathrm{h}\mathrm{e} {\mathrm{S}\mathrm{O}}_x$ emission generation coefficient, which depends on fuel quality (for example, for diesel fuel, this is about 0.001, and for LNG fuel, it is about 0.0); $∆\mathrm{C}\mathrm{O}$ is the $\mathrm{C}\mathrm{O}$ emission generation coefficient, which depends on the engine type and quality, which can be found in the engine specification; ${\mathrm{N}}_W$ is the average engine power during the voyage; $t$ is the voyage time; $∆{\mathrm{N}\mathrm{O}}_x \mathrm{i}\mathrm{s} \mathrm{t}\mathrm{h}\mathrm{e} {\mathrm{N}\mathrm{O}}_x$ emission generation coefficient, which depends on the fuel type and engine quality; $∆\mathrm{P}\mathrm{M} \mathrm{i}\mathrm{s} \mathrm{t}\mathrm{h}\mathrm{e} \mathrm{P}\mathrm{M}$ emission generation coefficient, which depends on the fuel type (for example, for LNG fuel, it is about 0) and engine quality.

In order to find optimal solutions, evaluation methods that use weight coefficients could be applied. Therefore, the comparative index ($K_L$) of SSS system services performed between ports or terminals could be expressed by assessing different factors (Equation (10)):

$$K_L={\displaystyle \frac{1}{{\eta }_L}}(k_P{\displaystyle \frac{P_{Li}}{P_0}}+k_T{\displaystyle \frac{T_{Li}}{T_0}}+k_D{\displaystyle \frac{D_{Li}}{D_0}}+k_E{\displaystyle \frac{E_{Li}}{E_0}}+k_{Ai}{\displaystyle \frac{A_{Li}}{A_{0i}}})$$

(10)

where ${\eta }_L$ is the correlation coefficient for the SSS system services (in a case where similar factors are considered—for example, while analyzing a few ports or terminals—this coefficient could be between 0.97 and 0.99, taking into account that more factors can improve identification of correlation coefficients using matrix systems); $P_{Li}$, $T_{Li}$, $D_{Li}$,$E_{Li}$, and $A_{Li}$ are the costs, time, distribution, and energy demand for the SSS services performed within the SSS system; $P_0$, $T_0$, $D_0$,$E_0$, and $A_0$ are the costs, time, distribution, and energy demand for ports or terminals, which can be determined by an expert or by applying other methods; $k_P$ is the weight coefficient of the SSS system services costs (this could be between 0.30 and 0.35 depending on the cargo type); $k_T$ is the weight coefficient of the SSS system services time (this depends on the type of cargo and could be between 0.20 and 0.25); $k_D$ is the weight coefficient for distribution services, which depends on the goods distribution requirements and could be between 0.15 and 0.20; $k_C$ is the weight coefficient of the SSS system services’ energy (fuel) demand, which depends on the number of logistics operations and could be between 0.20 and 0.25; and $k_{Ai}$, $A_{Li}$, and $A_{0i}$ are other possible factors and weight coefficients, for example, emissions, cargo weights, and other factors important for the SSS system services cases; the sum of the weight coefficients must be equal to one.

The methodologies presented in the sources [29,30,31,32] can be used to calculate emissions. When using alternative transport corridors, mostly using road transport, in Formulas (2) and (5)–(10), instead of the maritime transport part, it is necessary to enter the corresponding elements of the specific transport mode.

The calculation of the comparative index (Equation (10)) is based on multi-criteria methods. It can be applied to various tasks, for example, related to freight transportation using the SSS system or other modes of transport, including the environmental impact assessment, if several ports or terminals are involved in freight transportation processes, and the assessment of any transport chain. When applying the above equation, it is necessary to select appropriate weighting factors, which can be calculated using a matrix if a suitable database is available or by using expert methods if there is limited access to real data.

For the clarity of the developed model, a flow diagram has been prepared, in which the SSS comparative index and its calculation are based on the assessment of factors (flows), and the stages of the developed method are indicated (Figure 3).

For the calculation of the SSS comparative index and the final decision, the most important factors are first evaluated, i.e., transportation costs using the SSS system or other transportation methods, transportation time, distribution possibilities and costs, environmental impact, and possible other factors such as restrictions on crossing state borders, additional possible payments, and the like, using the SSS system or using other transportation methods. At the same time, the correlation coefficient must be evaluated if there are similarities between the factors and the factor weight coefficients. In all cases, regardless of the number of factors, the sum of the factor weight coefficients must be equal to one.

If the obtained SSS comparative index is satisfactory, the SSS freight transportation system is recommended. If the obtained SSS comparative index is unsatisfactory, it is necessary to separately evaluate the factors, the possibility of their optimization, and if, after this evaluation, the SSS comparative index is satisfactory, the SSS freight transportation system can be used. If the obtained SSS comparative index is not satisfactory, it is advisable to use other methods of freight transportation, for example, road, rail, or other combined modes of freight transportation.

The developed methodology can be used to assess and compare transport corridors, including SSS and alternative transport corridors. The methodology developed and presented in the article also allows it to be used in the presence of economic borders, since in the presence of economic borders (when carrying out transportation in more than one economic space), the speed of cargo transportation by different modes of transport may change. A change in the speed of a mode of transport may also lead to changes in other SSS or transport modes’ cargo transportation elements.

4. Case Study of SSS and Alternative Transport Corridors

Two ports were selected for the case study. ROPAX shipping lines and possible alternative transport corridors exist between these two ports. The ports of Kiel [33] and Klaipeda [34], between which a ROPAX shipping line operates, were selected for the research. ROPAX ships sail from both ports once a day (Figure 4) [35]. The land transport corridor between these ports can also be used (Figure 4) [36]. Each ship can carry an average of about 200 cargo vehicles at a time. The sailing time is about 19 h. The distance between the ports is about 407 nautical miles [35].

The cost of transporting one car and the terminals is about EUR 1000, so the cost of 150 vehicles is about EUR 150,000. The average power of the ferry’s main engine during navigation is about 18 MW, and the relative fuel consumption is about 0.15 kg/kWh. The total fuel consumption of the ferry during navigation and at the terminals is about 60 t.

An alternative transport system can be road transport (Figure 5). The distance between Kiel and Klaipeda is about 1530 km. The assessment assumes that one road vehicle transports about 20 t, and the average driving speed is about 70 km/h. The total driving time from Kiel to Klaipeda is about 36 h (driving time is about 24 h, and rest time is about 12 h). The average engine power of a tractor (truck) is about 280 kW, and the relative fuel consumption is about 0.12 kg/kWh. In this way, the tractor consumes about 1000 kg during the trip. When assessing the transportation of a similar cargo by ferry (150 road vehicles), the total net driving time is about 5400 h, and the total fuel consumption is about 150 tons. The average transportation cost for one vehicle is about 1.5 EUR/km, so the transportation cost would be about EUR 2300 or about EUR 345,000 for all vehicles (150 units).

When evaluating the adopted transportation systems, parameters, and emission calculation methodologies provided in [14,28,29,30,37], using SSS and road transportation between the specified ports, the emission results obtained are presented in

Table 1. Amount of emissions generated when transporting the same amount of cargo by SSS and road transportation systems.

Emission Type	SSS Using Diesel Fuel	SSS Using LNG Fuel	Road Transport Using Diesel Fuel	Road Transport Using LNG Fuel
${\mathrm{C}\mathrm{O}}_2$, t	176	148	640	540
${\mathrm{S}\mathrm{O}}_x$, kg	50	0	200	0
$\mathrm{C}\mathrm{O}$, kg	1710	1026	2520	1764
${\mathrm{N}\mathrm{O}}_x$, kg	3420	1368	3360	2016
$\mathrm{P}\mathrm{M}$, kg	171	0	34	0

.

When it is necessary to transport many cargoes or vehicles, the SSS system is in many cases much more advantageous in terms of time, cost, and environmental impact [36]. Using the comparative method presented in Chapter 3, it is possible to find out how much more advantageous the use of SSS can be compared to the use of other transport systems or to find out to what extent the use of SSS is more advantageous compared to other methods of transporting goods.

The comparative index, taking into account the cost of cargo transportation between selected ports (locations), transportation time, goods distribution options, energy (fuel) costs, and additional fees for generated ${\mathrm{C}\mathrm{O}}_2$ (calculating that the fee for one generated ton is EUR 70), is presented in

Table 2. Components of the comparable index and the comparable index for transporting goods of a size equivalent to 150 freight vehicles between Kiel and Klaipeda using the SSS system and road transport vehicles.

Parameter	20	500	1000	1500	2000	2500	3000
Number of units	1	25	50	75	100	125	150
Discount, %	0	5	10	15	20	25	30
$P_{Li}$, EUR	2300	57,500	115,000	172,500	230,000	287,500	345,000
$P_{SSS}$, EUR	1000	25,000	50,000	75,000	100,000	125,000	150,000
$P_{SSS}$, EUR with discount	1000	23,700	45,000	63,750	80,000	93,750	105,000
$T_{Li}$, h	36	900	1500	2700	3600	4500	5400
$T_{SSS}$, h	24	600	1200	1800	2400	3000	3600
$D_{Li}$, h	2	50	100	150	200	250	300
$D_{SSS}$, h	3	75	150	225	300	375	450
$E_{Li}$, t	1	25	50	75	100	125	150
$E_{SSS}$, t	0.4	10	20	30	40	50	60
$A_{Li}$$, ({CO}_2$), t	3.2	80	160	240	320	400	480
$A_{SSS}$$, ({CO}_2$), t	1.28	32	64	96	128	160	192

.

The difference in the direct price of freight transportation using the SSS system and an alternative mode of transportation, i.e., using the road transport system, is one of the factors, and as presented in the analyzed example, the cost using the SSS system is about 2.2–2.7 times cheaper (Figure 6). Due to the fact that using the SSS system, discounts are applied when transporting larger quantities, the time of use of vehicles is significantly shortened.

When processing the results of real experiments on freight transportation between Kiel and Klaipeda with real ships and road vehicles, the Kalman filter [38] and the dispersion method [39] were used to filter them, determining possible deviations (accuracy) in the results. For freight transportation time, deviations of up to 10–12% were obtained; for price, deviations of up to 12–15% were obtained; and for fuel consumption and, accordingly, emissions, deviations of up to 10–15% were obtained. In this way, it can be stated that the developed methodology meets the needs of scientific research and practical application in many cases.

The total vehicle utilization time ($T_{Li}$) and the cargo redistribution time at the terminal ($D_{Li}$) when transporting cargo by road vehicles and using the SSS system ($T_{SSS}$) and ($D_{SSS}$) differ significantly, especially the vehicle utilization time. The utilization time of road vehicles when traveling by road is about 25–30% longer (Figure 7). The cargo redistribution time at the terminal when using the SSS system is about 10–20% longer compared to cargo transportation by road, since the procedure time is reduced (no need to use the terminal) (Figure 7).

Fuel consumption $E_{Li}$ and corresponding emission ${\mathrm{C}\mathrm{O}}_2$ generated when transporting the same amount of cargo or road transport units using road vehicles and the SSS system (Figure 8) allow one to make the right decision regarding which freight transportation method is better to use. When transporting freight by road, about 2.5 times more fuel is consumed, and at the same time, about 2.5 times more ${\mathrm{C}\mathrm{O}}_2$ is generated compared to transporting the same amount of cargo using the SSS system.

When evaluating all possible factors, using the comparative index, the difference in freight transportation between the analyzed points (Kiel and Klaipeda) is from approximately 2.14 to 2.23 when transporting the same cargo surplus using the SSS system, if discounts are not applied in the SSS system, and from 2.23 to 2.52 if discounts are provided in the SSS system (Figure 9).

Based on the case study, using the SSS system when transporting relatively large quantities of cargo is up to 125-130% more optimal than direct transportation by road.

5. Discussions and Conclusions

The volume of freight transportation worldwide is constantly increasing. New transport options and methods are emerging that allow reduced freight transportation time, cost, and environmental impact while transporting the same amount of freight.

The article presents a methodology for a comparative index for transporting cargo using short-sea shipping and land transport systems which allows for assessing the advantages of SSS and the optimization of transportation itself. Theoretical and practical studies conducted by analyzing real transportation have shown that the SSS system can be applied in many cases, but at the same time, it is difficult to determine the critical volume of cargo transportation when the SSS system is superior; therefore, determining the optimal volume of cargo using the SSS system will be a direction for further research.

The developed methodology allows forecasting and optimizing cargo transportation using the SSS system and other possible transport corridors. However, evaluating the factor weight coefficients when adapting to specific conditions is also important, since their evaluation is very important in finding optimal solutions. Therefore, evaluating factor weight coefficients should be an important direction for further research.

Based on the research conducted, the following conclusions can be drawn:

• Short-sea shipping in those sea regions where RORO liner shipping is developed has good prospects for taking over a significant part of cargo from road transport.
• The “transition” of cargo from road transport to the SSS system allows for a significant reduction in transportation costs due to more optimal transport use.
• The reduction in cargo transportation time allows for a more optimal arrangement of cargo transportation capacities, especially when using sea RORO transportation, and reduces the wear and tear of road vehicles.
• Freight transportation using the SSS system significantly reduces the environmental impact in many cases, as emissions generated when transporting the same amount of cargo are minimized.
• The developed comparative SSS system index allows for sufficient accuracy of assessing quantitative parameters of freight transportation.

The developed SSS system assessment methodology and comparative index allow for optimizing freight transportation (transportation time and cost) while reducing environmental impact.