What is a Doodle Bug? It was a Steam or Diesel Railroad Engine with just a couple of Railroad cars that served as a commuter/shuttle ten mile "Short Line" railroad. Also often termed, LCL, (LESS than CARLOAD LOT).
Where I grew up in central Kansas, we had two main east/west railroad lines, the (1) AT&SF (Atchison Topeka and Santa Fe) and the Missouri Pacific, St Louis to D&RG (Denver & Rio Grande in Colorado). Somewhat parallel from 40 miles apart to ten miles or less in places. Where I lived, the two lines were separated by 10 miles. There was a connecting North/South railroad for the purpose of a shuttle freight back and forth between the two towns in Barton County, KS. As I recall, it was called a SPUR LINE. Midway, there was a Grain Storage Elevator with a Truck Scale, to receive and load wheat into RR cars. The elevator was termed DENTSPUR. From Great Bend, KS to the west, Santa Fe also had what they called a BRANCH RAILROAD LINE, to Scott City, KS. This was before the prominence of semis (tractor-trailer trucks). Most of these Short Lines were abandoned with the steel RR tracks and wood ties removed. Many were then converted to Walking/Horseback/Bicycle Trails.
My daughter showed me how to look up pictures on Google Images and I've had a lot of fun browsing through all the pictures. I found many of these pictures of Doodlebugs there:
As a sidelight to railroad talk, freight rates are based on Classification of product. I worked all my 54-year career as an accountant/comptroller at a meat packing plant. Often we would see freight bills with the term "NOIBN". I inquired what this classification represented. It means ''NOT OTHERWISE INDEXED BY NUMBER".
Another side light to this subject: This short line railroad was parallel to a Highway. In the years of 1930/1940, Central Kansas experienced an OIL BOOM. This time frame era brought with it what was termed HONKY TONKS or ROAD HOUSES. It consisted of a small convenience store with a Juke Box, improvised dance floor, short order restaurant and beer. In the five mile midway point of this ten mile road, was one such Honky Tonk, named "HALF WAY INN". Shortly thereafter, in the northwest area of our county, a farmer set up a similar HONKY TONK, and called it "ALL THE WAY INN". The Kansas Liquor Law in those years were termed DRY YEARS, NO LIQUOR LICENSES, ETC. And beer was restricted to 3.2% alcohol. H-O-W-E-V-E-R, as with any prohibition or DRY YEARS, there were generated what is termed BOOTLEGGERS. And with OIL BOOMS, as with the GOLD MINING BOOMS, the term SOILED DOVES follows. THUS, this set up with HONKY TONKS served as a resource for both the Bootlegger outlets and Soiled Dove facilities.