The road toboggan was a lever-operated four- to six-man sled powered by a motorcycle engine, and is essentially what you would invent if you wanted to combine Cool Runnings with those gruesome car accident videos they show in traffic school. It was capable of reaching a top speed of 90 miles per hour without the assistance of snow and/or gravity, apparently because nobody told its creator that sleds aren't supposed to need windshields. Also, nowhere in that diagram do we see any mention of the word "brakes," leading us to assume that the vehicle was designed to only be slowed by terrified screams.
The one-wheeled coaster was a child's toy built by an Austrian engineer, although it looks like something Jimmy Neutron would invent if he were born in a coal chute in 1925 and possessed of the single-minded purpose of depressing his fellow children. It's a scooter built inside a space-age ring, giving the lucky rider a glimpse of a future in which fun has been outlawed.
You may notice that the hoop isn't quite big enough for the little boy in the picture, treating him to the added joy of relying on early 20th century medicine to mallet the scoliosis out of his spine.
The treadmill wagon was designed by a man in Pennsylvania to be a multipurpose toy/exercise device for the whole family. It is essentially what you would get if you built a Segway for children, one that actually makes walking harder in a way that only Depression-era technology could.
By walking on the metal rollers, a kid could propel the wagon forward at the blistering pace of slightly slower walking, unless it was going downhill, at which point it would achieve the speed of hilarity. You could also put a board down inside of it and use it as a regular wagon, if for some reason you owned the treadmill wagon but weren't a lunatic. As an added bonus, Mom and Dad could turn the wagon upside down and use it as an old-fashioned stationary treadmill to help sweat away those war rations before drunkenly shouting Junior to bed and passing out in front of the radio.
The land boat was, astonishingly, a rowboat-shaped cart with wheels operated by two oarlike levers. Who built it or why is unclear, but needless to say, it didn't catch on (it seems unlikely that more than six land boats ever existed at one time). This is unfortunate, because the land boat was demonstrably superior to walking -- a single pull on the levers could "propel the car the distance of several strides," enhancing your afternoon constitutionals with the joy of tugging on giant metal switches like a trolley car driver while basking in the dead-eyed stare of a gussied up teetotaler. How can we claim that 1920s America was an intolerant society when these people weren't immediately beaten the moment they left the driveway?
So it's occurring to us that stationary exercise machines are apparently a modern concept, because it looks like there was a time in our recent history when people thought that exercise needed to involve actual forward motion and be ripping good fun. The late 1930s response was the whirligig car -- essentially a rowing machine designed for two people by a manufacturing company in New York. The "fun" of the whirligig car was that the rowers had to stay in sync with each other to avoid spinning the vehicle out of control and into a ravine.
In 1949, jet engines were not yet a decade old. The technology was still in its early stages, and test runs would catastrophically fail with some regularity. It was in this tumultuous time of discovery that some bold young engineers strapped a jet engine to a motorcycle to determine propulsion's suitability for ground-based vehicles, because what occasionally worked in the sky would almost certainly work screaming across the Nevada desert on 27-inch bicycle tires.
Armed with the experimental engine, the motorcycle topped out at a little over 70 mph on a test run without killing a single person. Modern motorcycles go almost three times as fast, killing, maiming and paralyzing countless people every year without the use of a jet engine. So honestly, this might be a picture of the least ridiculous motorcycle ever constructed.
For more ridiculous ideas from our ancestors, check out 18 Hilarious Modes of Transport Science Gave Up On Too Soon and