TRISTAN, the Triennial Symposium on Transportation Analysis, brings together top researchers from academia and industry in all areas of transportation science. The ninth edition of TRISTAN was held at the Aruba Marriott Resort in Oranjestad, Aruba, from June 13 to 17, 2016 and continued the tradition of scientific excellence and friendly networking. The organizing committee consisted of Andreas Hegyi, Bart van Arem, Adam Pel, Niels Agatz, Luuk Veelenturf and Alfredo Nuñez. The scientific committee accepted 193 papers from the 273 submissions. Our special section is devoted to publications based on work that was presented at TRISTAN IX.