The December issue of the On Balance Newsletter describes work by Professor Carolina Osorio that improves the efficiency of traffic simulators used to optimize design and operations of urban transportation networks. Osorio and Michel Bierlaire of the École Polytechnique Fédérale de Lausanne designed an optimization framework that bridges the high-definition results of a microscopic simulation model with the computational efficiency of a macroscopic analytical model. They addressed a traffic signal control problem in the city center of Lausanne, Switzerland, and their new methodology identified signal plans that lead to a 34 percent reduction in average trip travel time.