The growing mobility demand on large and medium world’s cities has been continually pressing transport authorities and urban planners to provide transit solutions with the required capacity, reliability & service level, safety and affordability. Matching all these requirements in a dense and constrained urban environment has not been an easy task, as the higher capacity solutions (i.e. rapid rail transit - RRT) often face technical (alignment constraints) and/or funding issues, while lower capacity solutions (both light rail transit - LRT and Bus Rapid Transit - BRT) generally face capacity and reliability constraints. While the former — generally underground — might counteract alignment and public utilities infrastructure incompatibilities, the latter often faces space (traffic interference), reliability and environmental constraints, that ultimately results in a constrained capacity and an unsatisfying service level.

Monorail technology is a transport system whose vehicles run on or suspended from a single track or beam, which is usually on an elevated and segregated structure. This technology was initially utilized to provide passenger transportation solutions for amusement parks and convention centers, but has now become a mature medium capacity transit solution for high density areas in cities around the world. Given its aerial concept, generally running above or bellow linear beams and, hence, above the ground, its structure is generally supported on vertical columns (poles), spaced up to 30 m (98.4 ft) along its alignment, requiring a reduced right of way (RoW), compared to conventional alternatives, which ultimately enables it to be fit in the median strip between the opposite lanes in the road system. Moreover, given the monorail’s technology vertical (grade) and horizontal (curve radius) alignment flexibility, it is able to provide medium capacity & high service level transit solutions, with a reduced land expropriation requirement, compared to the traditional transit solutions. Furthermore, its segregated right of way, associated with a driverless approach, makes feasible the use of smaller headways, with an inherent operational flexibility, in terms of capacity and service level, with lower operational costs.

Monorail operational features — generally running on rubber tires in contact with concrete or steel structures — provide a smooth and externally silent ride, for both passengers and the neighborhood. Moreover, the lighter vehicles allow the possibility of both a lighter support infrastructure and an improved energy performance. Finally, different from the bulky and noisy elevated rail structures, the monorail’s elevated structure is thin and light, which ultimately avoids the well known shadow effect, allowing an aesthetic friendly (or less intrusive) structure, to cope with the urban environment.

This work presents an overview of the monorail technology, with a review of its technical and operational features, based on the current available technical literature, highlighting the strengths and weaknesses of this promising technology for transit applications. The work also presents case studies, reporting some of the well known and successful monorail projects implemented around the world.

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