Kilometer 31 (Kilómetro 31 or km 31) is a 2006 Mexican horror film, written and directed by Rigoberto Castañeda. The film is inspired by the Crying Woman legend (La Llorona) and legends about highway ghosts.
Following a horrible street accident on a rural wooded road near Mexico City, Agata goes into a coma, and her identical twin sister Catalina begins to experience the pain and terror that her comatose sister is going through. Catalina must try to solve the mystery of her sister's accident next to the Km. 31 marker and discovers a local legend that tells of malignant spirits that prowl the road and who are said to prey on travellers. Following a series of terrifying events, Catalina realizes that their link is growing stronger and that her sister is screaming for help from her unconscious state. With the help of her Spanish boyfriend Nuño, Agata's boyfriend Omar, and local detective Martin Ugalde, she discovers that Agata is trapped between life and death, between reality and a terrible netherworld of evil spirits and ancient legend.
The film was released on February 2 and was on top in the Mexican box office that weekend. 
The film was released in select cinemas in the United Kingdom, with English subtitles, on December 7, 2007 after its premiere at the Empire Cinema in Leicester Square on 6 November 2007.
- EyeForFilm.co.uk interview with director Rigoberto Castañeda about KM31 and Blackout.
- Carmen Sánchez Dávila. “No hay peor miedo que al fracaso”, asegura Rigoberto Castañeda director de “Kilómetro 31”. Archived 2010-06-21 at the Wayback Machine. February 15, 2007. Filmeweb.
- Eunice Martínez Arias. Orgulloso de su ‘miedo’. February 24, 2007. El Siglo de Torreón.
- Fausto Ponce. Kilómetro 31: Una “pesadilla” hecha realidad. Revista Proceso.
- Km 31, vuelve el cine de terror mexicano. January 22, 2007. Quinta Dimensión.
- "Kilómetro 31" continua con éxito. February 28, 2007, La Voz.
- Rompe récord de asistencia Km. 31