Editing 4-4-4-4 (section)

===21st century===
Only one locomotive of the 4-4-4-4 arrangement is being constructed. When finished, [[Pennsylvania Railroad 5550|PRR 5550]] will be the 53rd and only surviving example of the PRR T1 class rather than a replica. The new build T1 is expected to implement some design improvements to help aid in solving problems encountered by the original 52. The estimated date of project completion is currently set to be around 2030.<ref name="T1Trust01">{{Cite web |url=https://prrt1steamlocomotivetrust.org/faq.php |title=FAQ Section - The T1 Trust |date=2016 |publisher=The Pennsylvania Railroad T1 Steam Locomotive Trust |access-date=23 April 2017 |archive-date=24 August 2019 |archive-url=https://web.archive.org/web/20190824010545/https://www.prrt1steamlocomotivetrust.org/faq.php |url-status=dead }}</ref> As of November 2023, the project is 43.3% complete with an estimated total cost of US $7,000,000.<ref name="T1Trust02">{{Cite web |url=https://prrt1steamlocomotivetrust.org/station/index.php?route=tinfo/tinfo |title=5550 Tender Preservation Fund |date=2017-08-21 |website=prrt1steamlocomotivetrust.org |publisher=Pennsylvania Railroad T1 Steam Locomotive Trust |location=Pottstown, Pennsylvania, USA |language=en |publication-date=August 2017 |access-date=2017-08-21 |archive-date=2017-08-21 |archive-url=https://web.archive.org/web/20170821170036/https://prrt1steamlocomotivetrust.org/station/index.php?route=tinfo/tinfo |url-status=dead }}</ref>