4-4-6-4

{{Short description|Duplex locomotive wheel arrangement}} {{More citations needed|date=July 2023}} A '''4-4-6-4''', in the [[Whyte notation]] for the classification of [[steam locomotive]]s by [[wheel arrangement]], is one that has four [[leading wheel]]s followed by four coupled [[driving wheel]]s, a second set of six coupled driving wheels and four [[trailing wheel]]s.

The [[Pennsylvania Railroad]]'s [[Pennsylvania Railroad class Q2|Q2]] class were the only locomotives ever to use this arrangement. These were [[duplex locomotive]]s, in which both sets of driving wheels were mounted in a common, rigid [[locomotive frame]]. This locomotive design was a further development of the highly successful [[2-10-4]]. The [[Divided drive (locomotive)|divided drive]], or [[duplex locomotive|duplex]] arrangement, allowed for higher speeds with less damage to the track.

A proposed design for the [[Lehigh Valley Railroad]] was done but it was never built.<ref>{{Cite web |title=Locomotives that were proposed, but never built. - Trains Magazine - Trains News Wire, Railroad News, Railroad Industry News, Web Cams, and Forms |url=https://cs.trains.com/trn/f/741/t/284694.aspx |access-date=2023-07-27 |website=cs.trains.com}}</ref>

Other equivalent classifications are:<br /> [[UIC classification]]: '''2BC2''' (also known as German classification and [[Italian classification]])<br /> [[French classification]]: '''2232'''<br /> [[Turkish classification]]: '''2435'''<br /> [[Swiss classification]]: '''2/4+3/5''' up to the early 1920s, later '''5/9'''

== References == {{Reflist}}

[[Category:4-4-6-4 locomotives| ]] [[Category:Whyte notation|46,4-4-6-4]]