We acknowledge the Portuguese Foundation for Science and Technology for funding Lígia Conceição's Ph.D. scholarship grant PD/BD/113760/2015 under the Massachusetts Institute of Technology Portugal Program in Transportation Systems.We acknowledge the Portuguese Foun dation for Science and Technology for funding Lígia Conceição’s Ph.D. schol arship grant PD/BD/113760/2015 under the Massachusetts Institute of Technology Portugal Program in Transportation Systems;