Sol Transit System Corporation was the company responsible for the running of the Interstitial Mass Transit System that linked all the worlds of the Sol system in the first half of the 22nd century prior to Dalek invasion. Its logo was described as resembling a red double arrow. STS most likely arose, whole or in part, from the Travel-Mat Corporation after that company's transmat network was dismantled as a result of events surrounding the Thousand Day War (TV: The Seeds of Death).