In 1996 the EU, with Directive 96/48/EC of the Council, laid the foundations for the development of the high-speed railway (HSR) network in Europe. In this definition are included the railway infrastructures constructed or upgraded to be travelled on at high speeds, and rolling stock designed fortravelling on those infrastructures [1]. In this way, the countries started or accelerated the plans for developing the HSR (e.g., in Italy, from 1998 to 2008, 32 billion euros have been invested [1]. In Italy, one of the first high-speed lines was the Milan-Bologna line, inaugurated in 2008, followed by a progressive upgrading of the entire national network. In the first ten years of life, the Italian high-speed railway doubled the number of trains per kilometer with an increase in passengers from 6.5 million to 40 million [1]. The reduction in travel times has triggered a modal shift toward the train and increased commuting between cities connected by high-speed trains. There are also effects on the real estate market and on tourism. Parallel with infrastructures, services must be developed to avoid the formation of bottlenecks that could negatively affect the system as a whole. Bottlenecks can be linked with the interaction between demand and supply, so actions are requested to optimize the system. For example, Armstrong and Preston [2, 3] analyze the capacity of the railway system at stations; similarly, Li et al. [4] proposed a method to optimize the capacity and train timetable simultaneously. Jovanović [5] developed an optimization model to design a railway station to maximize capacity. However, there are still other critical points that represent a barrier to the railway service. A typical example is represented by the maritime crossing and the necessary operations on the rolling stocks. In Europe, some of the main relevant examples are represented by the rail service between Sassnitz and Trelleborg and between Rødby and Puttgarden. For these connections, the train is no longer provided, on the contrary, in Italy, the connection between Sicily Island and the Italian peninsula is still active (Fig. 1). This represents a critical issue that affects the performance of passenger and freight flows.

Based on a real case, this paper deals with the temporal and spatial barrier represented by a discontinuity that exists at a hub of passengers. The situation analyzed is the railway connection between Sicily Island and Italy, supplied by a passenger train ferry service (performed by ro-ro vessels that embark/disembark the trains). The Strait of Messina marks the border between the Sicily region and the Calabria region (Fig. 1), two southern areas of Italy: they are among the most distant community territories from the demographic and economic center of gravity of the European Union. The geographical distance is amplified by the quality of the connections, which involves higher travel costs and times for the same distance traveled than those faced in central-northern Italy.

The crossing service on the Strait of Messina has allowed citizens and visitors to reach the Italian peninsula from Sicily and vice versa. Each year, more than 60,000 couches cross the Strait area, and approximately 2,600,000 passengers (about 7,100 per day) choose to cross the corridor by train [6]. In line with the increasing interest in more sustainable transport solutions [7] passenger rail transport represents the most valuable environmentally sustainable alternative [8, 9]. Therefore, an in-depth study of the services provided, and possible improvement strategies is of specific interest to the area. Infrastructure investments also positively affect regional GDP growth along the corridor, facilitating trade [10-12]. Furthermore, from the European point of view, interventions focus on removing barriers for passengers and freight on the continent [13-15]. Therefore, the interest in solving bottlenecks became a crucial task in European countries where, in recent years, significant financial and technological strengths were underpinned to improve rail infrastructure in favor of a more competitive development [16-18]. Consequently, several researchers investigated the potential benefits and infrastructural limits in transport corridors [19-21].

The Strait of Messina has always been a strategic node in the Italian transport system, and several researchers have focused on the needs and limitations of this area, approaching the critical reduction of supply by integrating both planning solutions and digitalization of the infrastructures [22-24]. Furthermore, Di Gangi and Russo [25] assessed the benefits of introducing a high-speed rail system for both Sicily and the Calabrian region; the study pointed out how travel times from Sicily to Rome by train can be drastically reduced by improving rail services; from this study also emerged how ferry services reduce the global performance of the system. Similarly, Musolino [26] focused on the integration between the two shores, highlighting how improving transport systems will contribute to the economies of the area.

This paper proposes some policy measures to reduce the effects of territorial discontinuity. Specifically, the paper contributes by defining some policies and measures to reduce crossing time for ferry passenger trains. It represents a step towards analyzing the train services for passengers. The proposed solutions concern short- and medium-term horizons; their introduction may require only new scheduling and a low budget, as well as new rolling materials and vessels, thus implying higher infrastructural costs. The proposed policies are specified considering the setup time.

All the information presented in the paper refers to public data, that can be consulted directly online, provided by the company that manages the studied railway service. Furthermore, data on vessel supply operating in the area also come from public archives and can be consulted online.

In summary, the purpose of the paper consists of evaluating the current situation of the transportation service to highlight strengths and weaknesses. Some possible policies are suggested, and middle-term policies are assessed, evaluating preliminary costs and set-up time. Such policies concern operations on rolling stock, land-side and sea-side changes.

The paper is structured as follows. Section 2 reports a brief literature review. Section 3 reports a summary of train-ferries services in Europe and the description of the Italian case. Section 4 reports the proposed measures (tactical and middle-term measures). Finally, the discussion on the obtained results and the conclusion.

Rail services, and in particular those provided by high-speed rail (HSR), affect user mode choices both for long-distance travel [27] and for adduction to other transport modes [28]. On long-distance travel, time uncertainties have more severe impacts on people from lower accessibility areas, increasing the inequity between groups of travelers, thus affecting the area's economic development of the area [29].

Albalate et al. [28] evaluated the impact of HSR services on the supply of air services in terms of seats and frequencies. Jiménez and Betancor [30] evaluated how the introduction of HSR services affects frequency, passenger rate, and airline market share. Bergantino et al. [31] analyzed HSR services considering two aspects: the competition between two different companies offering the service (the observed effect is an increase in supply) and the influence on the price of air services (the observed effect is a reduction in the price of the air ticket). Jiang and Zhang [32] considered the long-term impacts of HSR on airline alternatives showing that the presence of HSR services can lead 123 the airline to increase the market coverage and the social welfare. Takebayashi [33] studied the collaboration between airlines and analyzed whether this collaboration can reduce 125 airport congestion.

Lin et al. [34] explored the impacts of HSR on economic and urban development; the objective is to provide a set of policies to improve HSR services and contribute to economic growth. Fan et al. [35] analyzed how HSR contributed to increasing accessibility (also causes economic growth). Other works on this topic [36, 37] explored the role of HSR in regional economic disparity. The introduction of better services reduces the existing mismatch between regional areas and helps economies to develop, thus closing the discrepancy with the wealthiest area of the country [36, 38]. For such a reason, it also represents a way to help the general economic growth of the area and reactivate the productive system [39]. Therefore, the value of time and the reliability of the transportation system are essential factors.

Fig. (1). The Strait of Messina (background map: OpenStreetMap [22]).

Regarding environmental impacts, the authors report both positive and negative outcomes. As an example, Liu et al. [40] analyzed the variation in air quality in some cities after the introduction of HSR; the conclusion is that such a service can reduce emissions and improve air quality in urban areas. On the other hand, there are studies showing how the construction of HSR has a negative impact on the environment [41, 42].

Investigating attributes that affect the modes of rail-air transport, some authors [43-45] showed that elements such as travel time (or distance), price, and service frequency are the ones that influence the user's choice. A similar analysis for the choice between HSR and road passenger transport [46] highlighted choices are influenced by attributes such as fares, comfort, speed, and safety. Bergantino et al. [47] investigated the effect of distance and travel time on modal choice. The results indicated that the relevant attributes to choosing HSR are income, travel purpose, and age. Chiambaretto et al. [48] evaluated the willingness to pay users using, if available, the combined rail-air transport: the results are that users were considered as the main criterion, followed by luggage handling and the priority in the case of delay.

Another critical factor affecting the choices for rail services and the efficiency of the rail corridor is the dwelling time for operations [49, 50]. Sanudo et al. [51], through combined quantitative and qualitative analysis methods, stated how rail service users consider the fare system, travel time, and intramodality as the most important attributes to increase the quality of rail transport. Furthermore, similar studies highlighted how improving railway service always led users to be more sustainable in their choices, thus mitigating the effects produced by transportation [52, 53]. Erhardt et al. [54] focused on understanding the importance of frequency of service and travel experience as factors driving travelers’ choices on long-distance trips.

Furthermore, Mackie et al. [55] and Flugel [56] indicated that willingness to pay and time savings must be considered in relation to the nature of the trip. Karmarkar et al. [57] evaluated the willingness to pay passengers who reduce travel time using the HSR service: the aim is to understand the perception of saved travel time and contribute to the definition of policies for ticket prices and management strategies. To the knowledge of the authors, there are no works that consider the case of trains embarked on ferries. Therefore, this paper tries to fill this gap by describing an existing train-ferry system and proposing some policies to improve the performance of the system.

There are only a few cases of passenger train ferries in Europe, and only one in Italy is currently active. The cited services are one between mainland Italy and Sicily, one from Sassnitz in Germany to Trelleborg in Sweden, and one from Rødby in Denmark to Puttgarden in Germany. It is important to note that the current crossing service of the Strait of Messina represents the only service available for an urban area (more than 800,000 inhabitants [58].

The data used in the following analyses are collected online by consulting the official websites of the companies that offer (or offered) the crossing service. The data for the service between Sassnitz and Trelleborg come from [59] while those for Rødby and Puttgarden are from [60]. Data related to the Strait of Messina crossing service are from a few studies [6, 61, 62].

Referring to the Italian case, the data are analyzed to know the status of the system and formulate and assess some possible policies to update the service, in terms of operational time reduction. The method takes into consideration both rolling stocks and the vessels.

3.2. Strait of Messina Context

Sicily is the fifth most populous region in Italy. It accounts for approximately five million inhabitants during the summer season, and the presences on the island tend to double. For this reason, an efficient and flexible railway system makes it possible to move vehicles and people more sustainably than much more harmful transport by car or by plane. Taking into account the passenger trains that cross the strait (Fig. 2), the Sicilian railway networks are served by two different convoy configurations following, respectively, the Tyrrhenian director East-West towards Palermo and the North-South Ionian direction towards Catania. Generally, an intercity train (IC) coming from Catania (IC727) and another one from Palermo (IC728) proceed simultaneously to Messina where they are embarked to go to Villa S. Giovanni, where they are composed as a single train. Vice versa, the train coming from Villa S. Giovanni, in the Messina station, breaks down and comes to form two trains.

Concerning IC 728, the composition of the section coming from Palermo consists of a locomotive E.464 (a class of Italian railway electric locomotives) and four UIC-Z1¹ derivative carriages (three-second class and one first-class). The train coming from Catania consists of an E.464 locomotive, a second-class semi-driver carriage of UIC-Z1 derivation and three UIC-Z1 derivation carriages (two of second class and one of first class). The material is embarked on the ferry by placing the semi-driver carriage at the head to form a reversible composition at the Calabrian side with traction ensured by a pushing E.402/b locomotive.

The characteristics of the vessel supply are reported in Table 3. The reported lane length refers to the longest and the shortest available one, these values can be used as a benchmark for the direct embarkation of a blocked composition trainset. The values for the entire capacity are then reported also assessing the convoy capacity. The same also states how the vessel fleet has homogeneous cargo and geometrical characteristics.

The evaluation of service performance derives from the Trenitalia timetable (Table 4), considering the intercity pair 728 (from Palermo) and 727 (from Catania). The crossing time of IC 728 from Messina Centrale to the Villa S. Giovanni station is, according to the timetable (Table 4), even at 70 minutes, and, overall, from the arrival in Messina Centrale at the departure from Villa S. Giovanni, it takes 115 minutes. For Intercity 727, the time to cross the strait remains, according to the timetable, at 70 minutes. Overall, the arrival at Villa S. Giovanni to the departure from Messina Centrale requires 125 minutes. The details of the operations, reported in Table 5, can be used in both directions.

Table 3. Vessel supply, ferries characteristics [61].

Vessel (Name)	Capacity (Units)*	Total Length (m)	Lanes (Number)	Lane Lengths (m)
Scilla	16	440.30	4	92.80 - 136.30
Villa	16	440.30	4	92.80 - 136.30
Logoduro	12	440.30	4	92.80 - 136.30
Messina	16	449.54	4	94.53 - 133.31
Iginia	16	449.54	4	94.53 - 133.31

Note: * Mean capacity convoy considers a length equals to 26.40 meters

Fig. (2). A portion of the interest rail network (background map: OpenStreetMap [22]).

Table 4. Timetable trenitalia [62].

Intercity 728	Palermo	Roma Termini	-	Intercity 727	Roma Termini	Catania
Arrival	Departure	Station		Arrival	Departure	Station
---	07:00	Palermo Centrale	-	---	11:26	Roma Terini
09:35	09:37	Milazzo	-	16:52	16:55	Lamezia Terme
10:00	10:15	Messina C.le	-	18:00	18:20	Villa S. Giovanni
11:25	11:55	Villa S. Giovanni	-	19:30	20:05	Messina Centrale
18:34	---	Roma Termini	-	21:26	---	Catania

Table 5. Operational time.

Operation	Duration (min)
Disassembly in Messina Centrale	15
Move to embarkment	5
Embarking Operations	10
Ferry Service	35
Unloading to Villa S. Giovanni	15
Positioning in Villa S. Giovanni	5
Verify Continuity	30
Total Time	115

These times are defined as safe for considering any uncertainties (for example, bad weather). Taking into account a crossing time equal to 35 minutes, the remaining amount is attributable to the decomposition times for boarding the ferry. Once the convoy is reconstituted, before being cleared for circulation into the network, it is also necessary to consider the time associated with verifying the continuity of the braking system.

In the following proposed scenarios, the train breakdown will no longer be taken into account and the convoys from Palermo and Catania will be considered staggered. Short-term solutions are introduced, explaining the benefit of reducing the total crossing time. Solutions with a longer time horizon are introduced; these also concern infrastructure costs, new vessels, or the supply of new train sets, and similarly to the previous case, time reduction and preliminary direct costs are evaluated for each proposal.

The proposals illustrated in Section 4 provided an estimation of the costs and times needed to realize the proposed policy (Table 10).

The train costs assessment assumed the use of two pairs of convoys. The overall balance between the proposed solutions would also add the effect linked to the travel-time savings on the network. The proposed solutions are not mutually exclusive but could be progressively activated to improve the service without significant infrastructure costs. Considering this, as reported in Table 11, a schedule is also proposed to identify the implementation of various steps for the ETR400 that seems the most promising solution for a long-term service.

Within the preliminary study, where the direct costs and the performance improvement achievable by adopting the single strategy were analyzed (Tables 7 and 10), it emerged that solution B would require the highest monetary costs and a lead time similar to solution D without, however, offering significant advantages in terms of performance; therefore in the following solution B will not be further considered.

Solution A only considers the necessary times to organize and reschedule new services; all rolling stocks are already available. In this case, the lead time is only necessary for the operators to organize new timetables and fleets, and this would also represent a temporary solution to test the direct effects of introducing the new service. Before introducing solutions C and D, it will be necessary to assign and organize infrastructural procedures and technical solutions to design a new terminal to host the new fleet and trainset; the procedure could take at least six months. Consequently, solutions C and D can be introduced step by step; the procedure will begin with the assignment of new infrastructures and convoy assembly, achieving a primary step (12/17 months). The reduced ETR thus will be ready to embark on ordinary vessels. Finally, introducing a full ETR 400 on a new vessel will require at least three years.

The paper analyzed the current crossing condition on the Strait of Messina (South Italy). It proposed planning and infrastructural measures to improve the railway’s passenger services.

A better detail about the benefits obtainable from the improvement of the services will consider into account the system of supply and demand concerned: for example, by conducting a related analysis to the overall travel times on the various relations of which the crossing of the Strait of Messina represents a node, quantifying the benefits obtainable from the current demand.

Downstream of what has been explained, it is possible to derive some considerations. Some of the proposed solutions are immediate and would undoubtedly improve the quality of the service without requiring significant financial resources or long-term decisions. The progressive introduction of different measures will help reduce the infrastructural and financial costs and indirect costs associated with the construction site. It also implies not stopping or reducing the services offered. Therefore, the solutions will further improve the services and efficiency offered by the railways. The evidence reported in this paper could help the system managers choose how to improve the train passenger link in the Strait of Messina service with both land and sea-side interventions.

The main weakness of this paper is that there is no information on user behavior as the characteristics of the service vary; the integration of such information could be useful in designing the service. Therefore, the next steps will focus on assessing attitudes and intentions. The operation of a Stated Preferences survey could help determine a suitable trade-off to intercept higher market share levels for train passengers. Therefore, these results would represent an exciting place to organize a scenario hypothesis as a valuable alternative against the air solution, which today means, in 60% of cases [67], the most preferred solution for those people who must organize long-distance trips to reach the central-northern regions. A further advancement that could be made concerns the evaluation of environmental impacts in the assessment of strategies. This can be done both by considering the use of low environmental impact vessels and by evaluating how time reduction influences environmental impacts. A final consideration can be made by considering the bridge over the Strait of Messina. The possible construction of a bridge (currently in an advanced design stage) would be an alternative to the crossing service by ship. Under these conditions, there would be two distinct ways to cross the Strait of Messina, which are not necessarily mutually exclusive.