The AAR type A switcher truck is a diesel locomotive

Diesel locomotive

A diesel locomotive is a type of railroad locomotive in which the prime mover is a diesel engine, a reciprocating engine operating on the Diesel cycle as invented by Dr. Rudolf Diesel...

 truck

Bogie

A bogie is a wheeled wagon or trolley. In mechanics terms, a bogie is a chassis or framework carrying wheels, attached to a vehicle. It can be fixed in place, as on a cargo truck, mounted on a swivel, as on a railway carriage/car or locomotive, or sprung as in the suspension of a caterpillar...

 introduced by EMD and installed as standard equipment on most EMD switcher

Switcher

A switcher or shunter is a small railroad locomotive intended not for moving trains over long distances but rather for assembling trains ready for a road locomotive to take over, disassembling a train that has been...

 locomotives and on those of other manufacturers. It was designed by Martin P Blomberg and its US Patent was filed on Jul 6, 1937 and approved Nov 15, 1938 under . It was designed for switcher service where the more complex high-speed passenger locomotive trucks were not needed. The truck uses drop equalizers but does not have swing hangers as used on the Blomberg B

Blomberg B

The Blomberg B was a "B" diesel locomotive truck. These trucks were the standard EMD four wheel truck from the FT up until the GP60. EMD introduced the truck in 1936. Unofficially it is named after Martin Blomberg, who joined the company the year before...

 and others. A combination of coil spring

Coil spring

A Coil spring, also known as a helical spring, is a mechanical device, which is typically used to store energy and subsequently release it, to absorb shock, or to maintain a force between contacting surfaces...

s, and leaf springs, positioned fore-and-aft inside the drop equalizers, give a good balance of damping

Damping

In physics, damping is any effect that tends to reduce the amplitude of oscillations in an oscillatory system, particularly the harmonic oscillator.In mechanics, friction is one such damping effect...

. The wheelbase

Wheelbase

In both road and rail vehicles, the wheelbase is the distance between the centers of the front and rear wheels.- Road :In automobiles, the wheelbase is the horizontal distance between the center of the front wheel and the center of the rear wheel...

is 8 ft (2,438 mm).