4-2-2-0
{{Short description|Steam locomotive wheel arrangement}}
Under the Whyte notation for the classification of steam locomotives, 4-2-2-0 represents the wheel arrangement of four leading wheels on two axles, four independently driven driving wheels on two axles, and no trailing wheels. The arrangement became known as double single.{{cite book |url=https://books.google.com/books?id=DuTvDwAAQBAJ&pg=PA63 |title=L&SWR Drummond Passenger and Mixed Traffic Locomotive Classes |year=2020 |publisher=Pen and Sward Transport |language=en |page=63|isbn=978-1-5267-6984-8 }}{{cite web|title=The Evolution of Compound Locomotives |periodical=|publisher=|url=http://mikes.railhistory.railfan.net/r043.html |url-status=|format=|access-date=2023-07-08|archive-url=|archive-date=|last=|year=1935|language=en|pages=|quote=}}
Usage
This unusual wheel arrangement was first used 1884 by Francis Webb in LNWR No. 3026, a 3-cylinder rebuild of a Metropolitan 4-4-0 Tank engine.
File:James Toleman 1893 World's Columbian Exposition.jpg
In 1893, the arrangement was used by the British engineer Frederick Charles Winby for the locomotive James Toleman, built by Hawthorn Leslie & Company in Britain. It was exhibited at the World's Columbian Exposition in Chicago and then delivered to the Milwaukee Road.{{cite book |first=Angus|last=Sinclair |title=Development of the Locomotive Engine |url=https://archive.org/details/cu31924003627167/page/496 |year=1907 |publisher=Angus Sinclair Publishing Company |language=English |page=496-499}}{{cite book |first=John W. |last=Smith |title=F. C. Winby’s "James Toleman" |url=https://archive.org/details/sim_railroad-history_1928_17/page/n13/mode/2up |year=1928 |publisher=The Railway and Locomotive Historical Society |language=English |page=12-14}}
Between 1897 and 1901 Dugald Drummond of the London and South Western Railway used this wheel arrangement on two classes of divided drive locomotives, the T7 and E10 classes. The absence of coupling rods enabled the driving wheels to be more widely spaced than on a {{whyte|4-4-0}} locomotive and permitted the inclusion of a larger firebox{{cite book| first=D.L.| last=Bradley| title=Locomotives of the London and South Western Railway, Part 2| publisher=Railway Correspondence and Travel Society| year=1967| page=77}}
Six locomotives of the type were built which performed adequately, but the uncoupled drivers led to poorer balance and increased wheelslip compared to {{whyte|4-4-0}}s,{{cite web|title=London & South Western 4-2-2-0 Locomotives in Great_Britain|url=https://www.steamlocomotive.com/locobase.php?country=Great_Britain&wheel=4-2-2-0&railroad=lsw|access-date=2024-06-18}} thus the type was not perpetuated.