In the end, the PRR decided to stop development of the T1 class, replacing all examples by the mid-1950s with diesel units. All members of the class were scrapped. It is very likely the T1 may have had many of its shortcomings solved had the PRR not retired the short-lived class so soon. During its short service life, the T1 was rumored to have operated at higher speeds than the steam speed record set by the London and North Eastern Railway's Mallard, but the claims could not be officially verified. Several bush tramway engine types were built with this wheel arrangement. These were known as "16-Wheelers". Two notable builders were J. Johnson and Sons Ltd, Invercargill, and A & G Price, Thames, New Zealand. Currently, only one locomotive of the 4-4-4-4 arrangement is being constructed. When finished, PRR 5550 will be the 53rd and only surviving example of the PRR T1 class rather than a replica. Furthermore, 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 around the year 2030. As of November 4th 2019, the project is 34.1% complete with an estimated total cost of US $7,000,000. References Further reading 44,4-4-4-4