The Tweddle Collection lacks a single focus but rather augments materials from the same railroad companies in other Hagley accessions. Material issued to Tweddle by employers typically includes employee and public timetables, rule books, equipment operating manuals, and advertising brochures. Of particular interest are the manuals for the Acela high speed train and several classes of Amtrak diesel and electric locomotives, including the relatively unsuccessful HHP-8 and the workhorse AEM-7. A large number of the manuals are devoted to employee safety, to the cleanliness of the trains and ensuring a high level of customer satisfaction and to employee well-being, stress-reduction and the like.

The timetables and brochurse of other railroads, other than the PRR, are a random assortment, mostly from the East but also the transcontinentals. While there are some early examples, most are from the long decline of private passenger trains in the 1950s and 1960s. Aslo of note are small fact books and comic books distributed by the Association of American Railroads to elementary schools in the 1950s and 1960s, explaining the railroad industry when it was a more visible part of American life.

United Transportation Union material dates from the early 2000s, when Tweddle was a delegate to union conventions.

Advertisements are tear sheets from popular magazines that were traded as collectables. They include some from the PRR's J. Walter Thompson campaign of the late 1920s, but most are color ads from the 1940s through the early 1960s. There is a good sample from the World War II years with patriotic themes.

Artwork is mostly of PRR subjects, but includes color renderings of General Motors diesel locomotives, all of which were marketed to the enthusiast community. Some are limited edition prints, while others are mass-marketed reproductions of the railroad companies' own commercial art. There are two original illustrated brochures for the 1949 versions of the "Broadway Limited" and "Spirit of St. Louis."

Maps and drawings are also a mix of modern prints from company originals that Tweddle was able to obtain from the engineering departments of Conrail and Amtrak and others purchased as collectables. Subjects include Pennsylvania Station and the proposed re-use of the Farley Post Office, Sunnyside Yard, random pieces of PRR rolling stock, track maps of the Philadelphia and Chicago areas and a plan of the 1876 Centennial grounds.

Posters include purchased reproductions of PRR posters and originals obtained from Amtrak. Among the latter are ones advertising the high-speed Acela and the centennials of Washington Union Station and the Wilmington, Del., station.