The Severn Bridge was a road bridge connecting England and Wales.
Some time prior to the 456 incident, Captain Jack Harkness shot at an escaping alien with a plasma cannon on this bridge, blowing a massive hole into both the alien and the bridge, and causing the SUV to fall underwater. (AUDIO: Submission)
Gwen Cooper once drove across it toward England, and seemed to view it with some dread, giving a joking "farewell forever" to her husband, with whom she was talking. They continued to mark the occasion with humour, he asked if she "had currency" and Gwen added that she'd "had [her] injections". (TV: Children of Earth: Day One)
When driving across the bridge into Wales, Rex Matheson was surprised to learn that the two were separated, comparing it to the way New Jersey and New York were divided by bridges. He was frustrated to find that there was a toll to pay in order to cross. (TV: The New World)