Double-decker bus
The first commercial horse-drawn double-decker omnibuses were introduced in England in 1847 by Adams & Co. of Fairfield, Bow, then improved upon by John Greenwood, who introduced a new double-decker in 1852.
Double-decker bus
There have been attempts to build a triple-decker bus. The main problems with such vehicles are instability and also the risk of hitting trees or bridges. In almost all models the third level was a small compartment in the rear part of the bus, such as a triple-decker capable of carrying eighty-eight people from Rome to Tivoli in 1932 or the General American Aerocoach 3 Decker Bus of 1952. The only three-decker with a full-length third level ever built is the Knight Bus created by John Richardson for "Harry Potter and the Prisoner of Azkaban" cutting up two AEC Regent III RTs and putting them together. Although made by a special effects team for a movie, it was a functioning bus, which even went on tour.