 By the mid-17th century, sedans for hire had become a common mode of transportation.London had "chairs" available for hire in 1634, each assigned a number and the chairmen licensed because the operation was a monopoly of a courtier of King Charles I. Sedan chairs could pass in streets too narrow for a carriage, helping to alleviate the crush of coaches in London streets, an early instance of traffic congestion.A similar system later operated in Scotland.