Real-time and continuous monitoring through smart sensors is considered to be the evolution of traditional track testing, enabling the earlier detection of the main failure modes that degrade railway tracks. Through carrying out preventive maintenance operations, infrastructure resources may be optimized, leading to smarter and more sustainable infrastructure. For this reason, under the larger goal of creating a synergy with various types of sensors for railway tracks, this article presents a critical review on the different, currently available sensors for smart and continuous monitoring. Specifically, the most appropriate monitoring technologies for each of the main railway track failure modes have been assessed and identified, thus deriving the advantages and capacities of each solution. Furthermore, this review presents some of the main experiences carried out to date in literature by using sensor technologies, such as strain gauges, piezoelectric sensors, fiber-optics, geophones and accelerometers. These technologies have proven to offer appropriate characteristics and accuracy for the continuous monitoring of a railway track’s structural state, being capable of measuring different parameters, such as deflections, deformations, stresses or accelerations that would permit the technical tracking of various forms of degradation.

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Bituminous sub-ballast is considered as an appropriate solution for increasing the structural performance and durability of railway sub-structure. This is especially prominent due to the continuous development of trains, which are capable of circulating at ever faster speeds and transporting evermore freight. Thus, the base infrastructure for trains must also evolve both structurally and sustainably. In this sense, the use of high modulus asphalt mixtures can increase the bearing capacity of the structure, while with the addition of modified bitumen during manufacture could present a promising potential for the improvement of the structural performance and durability of the infrastructure. Therefore, this study focused on assessing the viability and potential benefits of using a high-performance asphalt mixture, manufactured with a highly rubberized low-penetration bitumen, for sub-ballast in railway tracks. To achieve this aim, the behaviour of the high-performance asphalt mixture was compared to a reference asphalt mixture, manufactured with conventional bitumen, which is typically used as bituminous subballast. A series of standard laboratory tests were carried out for both mixtures, as well as two innovative tests to better assess the main failure modes expected in railway applications. In addition, a cost analysis evaluated the economic impact of the high-performance asphalt mixture in comparison with the conventional solution. Results demonstrated that the proposed mixture presented a higher bearing capacity than the conventional bituminous sub-ballast, while reducing around 50% the permanent deformations and susceptibility to cracking under similar efforts. These results indicate that the layer thickness of the modified mixture could thus be reduced by half, and still offer similar mechanical performance to the conventional mixture. In turn, this would provide a potential economic saving higher than 30%, compared to the conventional standard solution for sub-ballast.