The Crusader 50 was a series of shuttle buses used by Crusader Tours for excursions on the planet Midnight. The Tenth Doctor rode one of these shuttles while Donna Noble relaxed at a spa on Midnight.
All windows were shielded during the trip due to the xtonic radiation of Midnight's sun and each bus was fuelled by micropetrol. Crusader vehicles never stopped in their crossings. Their air supplies ran on a "circular filter" which could recycle the same air for up to ten years.
The buses were also equipped with entertainment systems, though perhaps more than necessary, to give the passengers a way to pass the time during the long journeys the buses took across the planet. When the hostess attending to one of the shuttles turned on too many of the entertainment systems at once and flooded the bus with distracting noise, she unwittingly upset the passengers. The Tenth Doctor saw some of the grimaced expressions of the people onboard, covertly pulled out his sonic screwdriver, and disabled the systems, allowing the passengers to converse without interference, while the hostess simply thought it was a system malfunction.
Rose Tyler attempted to contact the Doctor from across another universe through a working screen on the shuttle, temporarily establishing contact just long enough to call out for him, but her message was muted and failed to be noticed by the Doctor, nor any of the other passengers.
The driver's cabin of one bus was destroyed due to the Midnight entity, vaporising both driver Joe and mechanic Claude, and Sky Silvestry and the hostess were blown out into the vacuum of space. (TV: Midnight)