This paper presents OTM-MPI, an extension of the Open Traffc Models platform (OTM) for running macroscopic traffc simulations in high-performance computing environments. OTM-MPI represents the frst open-source, distributedmemory, macroscopic simulation model developed for modern high performance parallel machines and large networks. Macroscopic simulations are appropriate for studying regional traffc scenarios when aggregate trends are of interest, rather than individual vehicle traces. They are also appropriate for studying the routing behavior of classes of vehicles, such as app-informed vehicles. The network partitioning was performed with METIS. Inter-process communication was done with MPI (messagepassing interface). Results are provided for two networks: one realistic network which was obtained from Open Street Maps for Chattanooga, TN, and another larger synthetic grid network. The software recorded a speed-up ratio of 198 using 256 cores for Chattanooga, and 475 with 1,024 cores for the synthetic network.