The Gregarious Railfan
Speeders and Handcars
Google images clik to enlarge  
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A speeder (also known as a railway motor car), is a maintenance of way motorized vehicle formerly used on railroads
around the world by track inspectors and work crews to move quickly to and from work sites.  Although it is slow
compared to a train or car, it is called speeder because it is faster than a human-powered vehicle such as a handcar.
Motorized inspection cars date back to at least 1896, when it was reported that the U.S. Daimler Motor Company
created a gasoline-powered rail inspection car capable of 15 mph.
In the 1990s, speeders were replaced with trucks (usually pickup trucks or sport utility vehicles) using flanged wheels
that could be lowered for on-rail (called road-rail vehicles or hi-rails for highway-railroad). Speeders are collected by
hobbyists, who refurbish them for excursions organized by various railcar owner associations.
Links
Speeders - Wikipedia   includes a list of manufactures  
The Section Car Pages (Australia and New Zeeland)   
Pictures these pictures are from the NAROA "for sale" web page: http://www.narcoa.org/forsale/4sale_want.htm    
clik to enlarge
Videos  
Handcars  
A Rail Speeder Adventure by Bill Christopher
Handcars - Wikipedia
A handcar (also known as a draisine) is a railroad car powered by its passengers, or by people pushing the car from
behind. It is mostly used as a maintenance of way or mining car, but it was also used for passenger service in some
cases. A typical design consists of an arm, called the walking beam, that pivots, seesaw-like, on a base, which the
passengers alternately push down and pull up to move the car.  Handcars were absolutely essential to the operation of
railroads during a time when railroads were the primary form of public transportation for people and goods in America,
from about 1850 to 1910.  They were commonly assigned to a "section" of track, the section being between about 6
to 10 miles long, depending upon the traffic weight and locomotive speed experienced on the section. Each section
would have a section crew that would maintain that piece of track. Each section usually had a section house which was
used to store tools and the section's handcar. Roughly 130,000 miles of track had been constructed in America by
1900. Thus, considering there was a handcar assigned to at least every ten miles of that track, there would have been
a minimum of 13,000 handcars operating in the United States.  A similar use vehicle called a velocipede designed to be
ridden by only one was similar to a bicycle with and outboard wheel to span to the second rail.
Pictures  
By Harvey Henkelmann - Own work, Copyrighted free use,
https://commons.wikimedia.org/w/index.php?curid=5377509
Videos
Handcar on railroad by aprilmr22
Velocipede by Featherbed Railroad
Wikipedia image
Google image, clik to enlarge  
Rail Go carts are something of a subset of Speeders. They are generally modern home made gas
powered affairs built by individuals specifically for traversing abandoned railroad rights of ways.