Darlington Street Railway
Although photographs of this very early horse tramway (1862-1865) have not survived, contemporary accounts indicate that tramcar crews wore uniforms. The Darlington Street Railway was promoted by American entrepreneur George Francis Train, the man behind the first true street tramway in the British Isles (Birkenhead Street Railway Company), as well as three separate lines in London (Marble Arch Street Railway; Surrey Side Street Railway; Westminster Street Railway) and one in Stoke (Staffordshire Potteries Street Railway). Staff working all these lines are known to have worn uniforms (likened by contemporary commentators to those worn by the Rifle Brigade), so the aforementioned accounts are entirely consistent with Train's approach to staff uniforms on the other systems he was involved in.
For a detailed history of early street railways, including Darlington, see: 'Pioneers of the Street Railway in the USA, Street Tramways in the UK…and elsewhere' by John R Stevens and Alan W Brotchie; Stenlake Publishing Ltd (2014).