An Italian road pavement design method for bus lanes: proposal and application to case studies

In urban centres, the presence of bus lanes is essential to facilitate public transport services for a better sustainability of the cities and reduction of private traffic and pollution. However, bus lanes need a specific geometric (i.e. road layout) and structural (i.e. pavement layer thickness) suitable design. The pavement design of bus lanes in urban areas is often performed using traditional methods, already used for other types of roads. Given the geometric and structural peculiarities of each road in the urban centres due to the historical city development, the application of these methods can lead to an incorrect road pavement design. For this purpose, a first attempt of a road pavement design system has been developed for bus lanes: it is a specific catalogue proposal for this type of lanes, which can support the technicians in evaluating the most appropriate solutions in terms of materials and thickness, for both new construction and maintenance. After evaluating the types and main characteristics of buses circulating in Italy, traffic levels (in terms of equivalent standard axle loads), subgrade bearing capacity and pavement structure were hypothesized. Assuming three possible structures and five traffic levels, a total of forty-four design solutions were drawn up. The required pavement thickness varies from 17 to 47 cm for a new lane construction and from 9 to 22 cm for an existing lane maintenance. All the proposed solutions have been verified by methods and models based on multi-layer elastic theory available in the literature. Moreover, their validity was evaluated applying the solutions to real cases. The results of this work encouraged the authors to improve the catalogue inserting solutions with natural stone, particularly used in historic centres for architectural and aesthetical reasons, and to differentiate the pavement thickness of bus lanes subject to high stresses (intersections, stops, etc.).