What is the purpose of a speeder shed - Model Railroader Magazine

Speeder shed  = Section house.

Divisions were broken down into sections. Each section had a section gang. They kept their rolling equipment in the section house. First handcars, then motorized section cars. The Fairmont Track car or motor car gained popularity in the 1930s and later. Handcars and velocipedes preceeded the motor car, knicknamed a "speeder" since they could travel much faster than a hand car.

Some of the models of motor cars were small enough that one man could extend a pair of handles and lift the car off the rails and allow regular train traffic to pass. Smaller cars were primarily for inspection use. Larger cars were called gang cars and they could carry six or eight men plus a trailer or two of tools and material.

They were frequently found at division points, then convenient junctions, depots  or sidings in between. Division points in the '50s were typically 100 miles or so. There might be five or six maintenance sections in between. Some larger section houses I've seen could keep six or eight cars in them. They were closer to the main tracks rather than deeper into yards.

Here is a pair of section cars to the right, off the main, as #6 rolls by.

NKP_PE6 by Edmund, on Flickr

 I used to have a Fairmont model MT-14 that I would run around on a short-line or on NARCOA trips:

Fairmont_0005 (2016_08_17 08_08_12 UTC) by Edmund, on Flickr

You can see the aluminum handles extended here as we place it on the track. 

Here's a typical B&M section house. There was planks across the track to aid in turning the section car and rolling it into the house.

BnM_section house_2 by Edmund, on Flickr

BnM_section house by Edmund, on Flickr

 A Hi-Railer is just as the name implies, a vehicle that can be operated on the highway or rails. The idea goes back probably a hundred years or so. Newer versions allow larger trucks and cranes to also operate on highways and, using retractable wheels, can be operated on rails as well.

Here's an early Hi-Railer on the NYC stopped in front of a section house:

NYC408 by John W. Barriger III National Railroad Library, on Flickr

 ...and another at Newton Falls, Ohio:

NYC516 by John W. Barriger III National Railroad Library, on Flickr

Hope that helps, Ed