Hamilton-Jacobi equations for optimal control on multidimensional junctions

We consider continuous-state and continuous-time control problems where the admissible trajectories of the system are constrained to remain on a union of half-planes which share a common straight line. This set will be named a junction. We define a notion of constrained viscosity solution of Hamilton-Jacobi equations on the junction and we propose a comparison principle whose proof is based on arguments from the optimal control theory.