Under the Whyte notation for the classification of steam locomotives, a 2-8-8-8-8-2 has two leading wheels, four sets of eight driving wheels, and two trailing wheels. Because of its length, such a locomotive must be an articulated locomotive. It is not longer than a normal articulated; the fourth set of drivers is located under the tender.
Other equivalent classifications are:
UIC classification: 1-D-D-D-D-1 (also known as German classification and Italian classification)
AAR classification: 1-D-D-D-D-1
French classification: 140+040+040+041
Turkish classification: 45+44+44+45
Swiss classification: 4/5+4/4+4/4+4/5
The equivalent UIC classification is to be refined to (1'D)DD(D1').
In June 1914, George R. Henderson was granted US Patent 1,100,563 for a quadruplex locomotive, which was assigned to the Baldwin Locomotive Company. Baldwin submitted a design for a 2-8-8-8-8-2 quadruplex to the Atchison, Topeka, and Santa Fe Railway.
The proposed quadruplex was essentially a cross between the cab-forward locomotives for the Southern Pacific and the Triplexes built for the Erie and Virginian, with a cab at the front for the driver and the rear cab for the fireman. It was a compound locomotive - the front boiler fed the front set of high-pressure cylinders, and their exhaust fed the next set back of low-pressure cylinders. Similarly, the rear boiler fed the rear set of high-pressure cylinders, and their exhaust fed the next set forward of low-pressure cylinders. The exhaust from both sets of low-pressure cylinders was vented to the atmosphere.
- US patent 1100563, Henderson, George, "Locomotive", issued 1914-06-16, assigned to Baldwin Locomotive Works
- "The Quadraplexes". www.douglas-self.com. Retrieved 28 October 2018.
- Solomon, Brian, 2015. The Majesty of Big Steam. Voyageur Press. ISBN 978-0760348925
- Drury, George H. (1993). Guide to North American Steam Locomotives. Waukesha, Wisconsin: Kalmbach Publishing Company.