Previously obtained RHRS results were complemented with trajectory simulations of potentially detachable blocks at mountain slopes that margin a segment of the SP-055 (or BR-101) highway. The study area is located in the city of São Sebastião, northern coast of the São Paulo State (Brazil) which has been historically affected by mass movements and rockfalls. This work details the risk analysis regarding the users of the highway presented by Castilho et al. (2018) combining RHRS risk assessment (Budetta 2004) with computer simulations of rockfall trajectories. The RocFall® software analyses demonstrate that even segments without rock outcrops at the road margins are prone to rockfalls in cases of detachment or landslide. Results show that in most cases the rocks strike the highway with a kinetic energy sufficiently high to inflict damage to its infrastructure and users. This work can be used by highway authorities to plan geotechnical measures and future surveying.

1 Introduction
1.1 Geological risks and transport corridors

Highways bordering rugged mountainsides suffer with slope stability problems worldwide, causing several physical, material and financial damage to their users and adjacent communities. According to Ranh (1986), a risk (geological or else) is defined as a potential hazard to human life and properties. This definition implies that a natural event regardless of the damage level should not be considered risky if there is no possibility of accident, that is, the human presence transforms an event into a risk. The possibility of accident occurrences – induced by human activity or not – endangers all the people and properties involved. In this case, a risk situation is only characterized whether geological information are linked to social and economic circumstances (Bolt et al. 1975).

In case of transport corridors such as highways and railways, a natural event would certainly result into some level of risk considering that human lives and the infrastructure itself would be compromised. Another aggravating feature in this scenario is that the individuals are in motion. A car driver or the passenger of a train could be at a speed that increases the danger situation, so the risk, or the potentiality of an accident, is bigger. Risk evaluations are performed in order to anticipate or prevent hazards and to mitigate the effects.

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