Time evolution of the timescale for planetesimal-planetesimal collisions for the nominal Solar System simulation. The collision timescale was calculated using Eq. (20) and assuming an initial planetesimal mass of 16 M_⊕ per gap edge. The dotted line marks where the collision timescale equals the time of the simulation. Since the resulting collision timescale for one planetesimal is several orders of magnitude larger than the actual simulated time, planetesimal–planetesimal collisions can be safely ignored in our simulations and will not constitute a significant path to replenishing the dust component in the disk.