[en] The harmful effects on citizens' health caused by the emission of air pollutants from the load transport such as, sulphur oxides (SOx); nitrogen oxides (NOx); methane (CH4), carbon dioxides (CO2) and particles emission (PM2,5/PM10), have motived an increasing concern in the public opinion. The need to integrate the economic development with the environmental sustainability that permits to ensure the standards of the European quality life for the next generations have leaded to new strategies in the European Policy of the intracommunity transport (short distance) taken by the European Union which are focused on the intermodality. This is so, due to the fact that the land transport was traditionally accepted as the most polluting transportation alternative for the load transport and otherwise the maritime transport proved to be the most sustainable one. Nevertheless, several aspects have currently carried to discuss these assumptions: the technical features of the vessels which operate under Motorway of the Sea conditions (Short Sea Shipping integrated in intermodal chains) do not favour the environmental sustainability; small and fast vessels which must be able to respond to the intermodality requirements, the unbalanced development of the limitations in the emission of pollutant agents in the European Union for the different transport systems. Whereas the European normative about gas emissions for the road transport were quickly tightened by forcing the technological development of solutions to increase the sustainability of the vehicles, the European maritime normative remains are supported by the IMO (International Maritime Organization) normative. This one, with international character beyond the European Union, results to be much slower in the establishment of the compulsory restrictions for the pollutant emissions. Due to the previous arguments the convenience of the maritime transport for the loads in short distance are currently under discussion. The published studies about this issue in the European Union are very scare and most of them are focused on technical solutions to reduce the pollution of vessel which operate in ECA (Emission Control Areas) and SECA zones (Sulphur Emission Control Areas). In other words, they try to offer technical solutions to accomplish with OMI normative by evaluating their economical impact from the standpoint of operation and investment but without evaluating their environmental impact with regard to the unimodal alternative. The highest expectations are provided by the use of gas based engines. However numerous recent publications alert about the existence of other pollutants which are not being regulated by the IMO but very harmful. Concretely, the methane slip due to the incomplete burning and bunkering operations for the gas maritime engines have alerted to many countries about the risk of greenhouse effect of the methane (25 times the CO2 effect). Due to the fact that the European Union have shown numerous times its intention to develop an own environmental normative for the maritime transport, it is expectable that in a next future this is a reality and its requirement level is comparable to demanding levels for the European road vehicles, Euro VI technology. Consequently, the present dissertation tries to tackle this issue which has been scarcely attended taking into account that the adaptation of the vessel fleets to the Short Sea Shipping in Europe has been become in an immediate challenge due to the expected new environmental restrictions (they will be comparable to the road ones) and to the need to keep the competitiveness of the intermodal chains against the conventional transport modes. Therefore, this dissertation tries to widen the current methodological framework of the optimization of fleets for the Short Sea Shipping traffic in Europe which must be integrated in intermodal chains with the comparative analysis of the environmental impact of the fleets and their intermodal chains regarding to the unimodal transport; this traffic is called Motorways of the Sea in the European context. The thesis will try to obtain a tool capable to define the optimal fleet from a technical and operative standpoint which offers competitive intermodal solutions to the unimodality in terms of time, cost and sustainability. For that, it will be necessary to define the different propulsive solutions not only from a technological standpoint but also by considering the combustibles associated to them, their impact in terms of the environmental costs, operative costs, investment costs, maintenance costs and the reduction of the cargo capacity by ensuring the required stability for the vessels. Thus, it will be necessary to propose a calculation system for the emission coefficients of several pollutants and their unitary costs. These results must be integrated in a mathematical model which will resolve the definition of fleets of optimal and feasible vessels by ensuring the highest competitiveness of the intermodality with regard to the unimodal alternative for the door to door transport. Thus, optimization process of this complex mathematical model will be carried out with multi-objective genetic algorithms. The Research Group associated to this thesis has developed a methodology for the optimization of fleets operating under Maotorways of the Sea Conditions. However, this thesis tries to advance in that research line by providing the environmental impact in the definition and evaluation model of the relative competitiveness between transport modes and ensuring the technical feasibility of the obtained fleets with the stability analysis of the vessels. Finally, the actual dissertation will try to be a making decision tool about the sizing and operation of fleets and their vessels, which by operating in short sea shipping conditions, provide sustainable solutions to the real transport needs. The proposed solutions will be to possible propulsion plants and their optimal combustibles. Therefore, the results will be useful not only for the ship-owners but also for the policy makers who will be able to evaluate in quantitative terms which solution must be supported from the administrations and how this can be included in the strategies of the transport policy. The consequence of the unbalance treatment from the Institutions to the different transport modes will be analysed as well.

[es] El impacto perjudicial en la salud de los ciudadanos de las emisiones de agentes contaminantes tales como el óxido de azufre, óxidos de nitrógeno, dióxido de carbono, metano, así como de partículas derivadas por el transporte de mercancías han motivado una creciente preocupación en la ciudadanía. La necesidad de integrar el desarrollo económico con la sostenibilidad medioambiental de modo que permitan garantizar los estándares europeos de sociedad de bienestar a las próximas generaciones ha llevado a la Unión europea a proponer estrategias en la política europea de transporte intracomunitario (corta distancia) basadas en la intermodalidad, ya que tradicionalmente se aceptó que el transporte rodado de mercancías era el más contaminante y el transporte marítimo el más sostenible. Sin embargo, varios hechos han puesto en cuestión estas hipótesis: las características técnicas de los buques que operan en régimen de Autopista del Mar (tráfico marítimo de corta distancia integrado en cadenas intermodales); buques pequeños y rápidos que deben ser capaces de dar respuesta a las cadenas intermodales y la desigual evolución normativa de las limitaciones en emisiones de agentes contaminantes para los distintos métodos de transporte en la Unión Europea, no favorecen la sostenibilidad medioambiental. Mientras que la normativa europea sobre emisiones del transporte terrestre se ha endurecido rápidamente forzando a desarrollar tecnológicamente soluciones de vehículos más sostenibles, la reglamentación marítima europea sigue apoyándose en la normativa OMI (Organización marítima Internacional), de carácter mundial, resulta ser mucho más lenta en forzar restricciones medioambientales. La presente tesis pretende ser una herramienta de decisión sobre el dimensionamiento y operación de buques y flotas que operando en tráfico regular de corta distancia ofrezcan soluciones a las necesidades de transporte. Las soluciones propuestas estarán vinculadas a alternativas de plantas propulsoras y combustibles óptimos. Los resultados no serán sólo de utilidad para armadores sino también para los legisladores que podrán valorar en términos cuantitativos qué solución puede apoyarse desde las administraciones de cara a establecer estrategias en la política de transporte y cuáles son las consecuencias del trato desigual a los distintos modos de transporte.