CAPRA: A contour-based accessible path routing algorithm

Existing journey planners and route recommenders mainly focus on calculating the shortest path with minimum distance or travel time. However, elderly people and those with special needs (i.e. those in wheelchairs or walking with sticks) often prefer a safer and more gentle journey. Given that their route options are affected by accessibility issues such as climbing a steep slope, it is important to design a journey planner that takes in to account the accessibility of the route, as well as the standard metrics, such as travel time and distance. Accessibility has not been explored widely in path finding problems. There are two key challenges for computing accessibility. First, the accessibility of a route is not well-defined. Second, the accessibility of a route varies from user to user. In this paper, a new algorithm is designed to tackle the above two challenges. Two metrics are defined to reflect the accessibility of a route, in terms of the total vertical distance and the maximum slope. Then, a multi-objective A* search algorithm is designed to obtain a set of Pareto-optimal routes in terms of the total distance covered and the two accessibility metrics. The user can then choose from the routes provided by the new algorithm, the most suitable one according to their own preferences. The experimental results show that the proposed algorithm is able to provide a diverse set of routes with different accessibility options, including the shortest path which does not consider any accessibility metrics. In other words, the new journey planner can satisfy the preferences of a wide range of users including both the healthy and those with special needs.