Trains are great!

Shay locomotives

Some of my favorite locomotives are those produced by Lima Iron Works, based on the patents of Ephraim Shay (1839–1916). These Shay locomotives were the most successful of the various geared locomotive designs.

Closeup of the three pistons
which drive a Shay locomotive
The bevel gears which connect
the drivetrain to the drive axles
Shay locomotives feature a side-mounted driveshaft which is turned by either two or three pistons, depending on the class. The driveshaft then turns a bevel gear which powers the driven axles.
Photo sources: Wikimedia Commons, Wikimedia Commons

The drivetrain was modified from the original patent designs by Lima Iron Works, mainly to feature shorter gearing. This increased torque at the wheels, making Shays especially useful for logging and other fields which required steep ascents. This tied back to Ephraim Shay's impetus for developing this novel drive system in the first place: his dealings in the logging industry.

Early diesel switchers & road switchers

An EMD SW1500 freshly painted in
NASA blue and white, with thin red stripes separating
An EMD SW1500 of the NASA Railroad at Kennedy Space Center. This photo was taken after fifteen months of refurbishment to repair damage from extensive corrosion.
Photo source: Wikimedia Commons

I've always had a soft spot for early diesel in North America, before railroads converged on forms like the GP-38 and so forth.