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.
OC Transpo Route 61
In the summer of 2006 and the winter of 2007, OC Transpo tested a double decker bus, the Alexander Dennis Enviro500 on this route as well as some express routes. The testing was made in order to determine whether double decker buses will be possible to operate within the Ottawa system as it contains a higher seating capacity than the articulated buses although with lower total capacity (including standing room only) than the latter due to the height restriction of the upper floor of the bus. . Double decker buses were re-used on the route during the summer of 2009.