To reduce runtime, can we combine multiple computers to run simulations in PTV Vissim? For large networks, we currently separate out simulation runs to multiple computers and then combine the results.

You cannot accelerate one simulation run by using multiple computers, but you can use multiple computers for running different simulation runs, e.g. different scenarios or different random seeds. There is no functionality yet in PTV Vissim to distribute the simulation runs on different computers such as the PTV Visum calculation server.