Cary Fukunaga follows up his 2004 short “Victoria para Chino,” about Mexicans smuggled into Texas in a semi, with his feature that observes two teens riding trains through Mexico. Sayra (Paulina Gaitan, “Innocent Voices”) is a Honduran traveling to New Jersey with her father and uncle. Riding atop a freight train, she encounters Willy (Edgar Flores) from the Mara Salvatrucha gang brotherhood who crossed his boss, Lil’ Mago (Tenoch Huerta Mejía) by lying about a girlfriend, Martha Marlene (Diana García), outside the gang. During a predatory raid on train travelers, Willy kills Lil’ Mago. Now on the run from his crime family, Willy finds an ally in Sayra. Although the sentiments and fates may be familiar, “Sin Nombre” is dense with ethnographic detail about gang organization and labor migration. This first feature deserved the directing and cinematography awards it won at Sundance this year. Fukunaga has cited the lustrous landscapes of “Days of Heaven” as one inspiration. Mexican vistas envelope an upbeat adventure for better futures, an on-the-road romance, reportage on the human economy of our hemisphere and a suspenseful chase by a vengeful brotherhood. Executive produced by Diego Luna and Gael Garcia Bernal from “Y Tu Mamá También” and the upcoming “Rudo y Cursi.” With Kristian Ferrer, Karla Cecilia Alvarado, Giovanni Florido, Gabriela Garibaldias and Liliana Martinez. 107m. (Bill Stamets)