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.
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Started as an experiment, GB had the 'Bulleid Double Decker' car SR Class 4DD in operation more than 20 years from 1949 to 1971. As the compartments were alternately high and low, to ensure that the overall height of the unit was within the clearances necessary to pass through tunnels and under bridges, the 'Bulleid Double Decker' was more a split-level than a true double-decker.