We report a global accurate double-sheeted potential energy surface for the lowest doublet states with (2)A '' symmetry of the N-3 radical using the double many-body expansion method. The functional form ensures by construction the degeneracy of the two adiabatic sheets along the D-3h line and the corresponding cusp behavior. Calibrated from multireference configuration interaction energies, it reproduces all the predicted stationary structures on both sheets and ensures a correct description of the dissociation limits. A test quasiclassical trajectory study of N(D-2) + N-2 collisions is also reported in the lowest adiabatic sheet of the potential energy surface. The results commend it for both classical and quantum dynamics studies, while serving as a building block for the potential energy surfaces of larger nitrogen allotropes and azides.