A shuttle bus service is a public transport bus service designed to quickly transport people between two points . Such a bus will shuttle backwards and forwards between the two points, normally without any intermediate stops and with a high frequency of trips. Such services are often designed to serve specific customers, such as hotels, attractions, park and ride routes or airport bus services. They may also be used to replace train services when rail lines are closed (for maintenance, or during emergencies). Unlike regular bus routes shuttles are usually but not always free of cost.