© 2018 American Physical Society. A phase space boundary between transition and nontransition trajectories, similar to those observed in Hamiltonian systems with rank-1 saddles, is verified experimentally in a macroscopic system. We present a validation of the phase space flux across rank-1 saddles connecting adjacent potential wells, and we confirm the underlying phase space conduits that mediate the transition. Experimental regions of transition are found to agree with the theory to within 1%, suggesting the robustness of phase space conduits of transition in a broad array of two or more degrees of freedom experimental systems, despite the presence of small dissipation.