The Knight Bus is a method of magical transportation in the Harry Potter novels which turns up to provide assistance to witches and wizards in need, who hail it by raising their wand hand. A trip on the Knight Bus can also be scheduled if a witch or wizard has a specific journey in mind. In Harry Potter and the Prisoner of Azkaban, the Knight Bus is described as being a “triple decker, violently purple” bus, probably modeled after the traditional red double decker buses common in muggle London. Due to the discomfort of riding on the Knight Bus, it is used as a transit method of last resort by most witches and wizards. The bus appears to be invisible to muggles.
The decks of the Knight Bus are accessed by spiral staircases, and the interior of the bus is lit with candles in sconces on the walls. During the day, the Knight Bus is equipped with chairs for passengers to use, while at night, the chairs are turned into beds. A fare of 11 Sickles pays Harry Potter's way from Little Whinging, Surrey to London in Harry Potter and the Prisoner of Azkaban, and for an additional two Sickles, Harry has the option of hot chocolate. Two Sickles more will also provide the passenger with a hot water bottle and a toothbrush.
In the books, the Knight Bus is staffed by Ernie Prang, driver, and Stan Shunpike, conductor. In the films, a shrunken head was added to the crew of the Knight Bus. Ernie and Stan are the names of J.K. Rowling's grandfathers, while in British slang, a Shunpike is a back road which can be taken to avoid a toll. “Prang” is also British slang, and originates from the Royal Air Force in the Second World War, which referred to a motor vehicle or airplane crash as a prang. Both staff members sit on large armchairs in the front of the bus, and Shunpike jumps out when the bus stops to assist passengers with their luggage. In Harry Potter and the Half Blood Prince, Shunpike was wrongfully imprisoned on charges of being a Death Eater.
The Knight Bus can travel like a regular bus, but appears to be able to achieve greater rates of speed, although travel is not comfortable, as the bus rattles and appears to be about to crash into obstacles constantly. In addition, the bus sometimes makes sudden leaps from location to location, accompanied by jolting and banging. These leaps seem to resemble apparation, another magical method of transportation which is usually undertaken by a single witch or wizard. The Knight Bus is also not capable of traveling underwater, but presumably can leap over it to travel around England, Scotland, and Wales.
The name of the Knight Bus is probably a pun on London's Night Buses. Like most major metropolitan areas, London runs less public transportation lines at night, and shuts down the subway altogether after a certain hour. To compensate, Night Bus routes run along major thoroughfares of the city to provide transportation. As any resident of a city who is waiting for a bus at three o'clock in the morning knows, any bus is a welcome sight, and the drivers also tend to drive more rapidly and recklessly because there is less traffic on the road.