I've been burned a bit recently by over-enthusiasm with respect to technological speculation. That said, at some point in my timeline I want to really explore what could happen differently with respect to the internal combustion engine. For example, it seems like there could be a kind of legacy technological relationship with respect to coaches, carrying over from the days of animal propulsion to mechanical propulsion. We are used to thinking of an engine and passenger compartment on a common chassis, but what if instead you had a base technology of coaches and attachable engines?
So let's say you have the Roth family of Bayern, who want at some point in the recent past to vacation in Norway to see the scenic fjords. "Ach, Norwegen!"
With OTL automotive technology, they would drive to Jutland, then perhaps take a ferry across. Or alternately, drive to an airport, fly, and then rent a car.
In ATL automotive technology, they would drive to a local station. There they would disengage the engine, attach their coach to a train pulled by an engine as if it were on rails, and ride a kind of segmented bus composed of their own coach and other coaches to Jutland. There the train of coaches would board a ferry. The engine remains behind after it loads the train on the ferry to make a return trip. The train of coaches travels on the ferry to Oslo, or for the sake of argument, Christiania. There it is unloaded by an engine specific to the purpose, and a service there rents engines, attaching different ones to each coach. The family then drives north on its own scenic tour.
What's gained is some of the efficiency of train travel, with one engine pulling multiple loads in a kind of combination train/tractor trailor/bus. But you also get the versatility of the automobile, with the family on vacation reaching its destination able to split off and travel in their own direction, not having to follow a set of rails, meet a schedule, or sleep while on a moving train (which Mutti just can't do).
The coach would actually be more spacious than the cab of most automobiles. Imagine three benches. The middle is reversible, and can face the rear with leg room for people to face each other. The front is more used for driving when the coach is engaged to its engine. Among the amenities is a folding table buried in the floor that the family can use to eat snacks on, conduct card games, and do homework on the trip.
On its surface you might think, wow, this is really imagining Europeans behaving in a very American way with respect to their internal combustion vehicles, riding around in these things half-SUVs and half-winnebagos. Of course, that's among the many cultural tendencies the timeline deconstructs. It presupposes Europe from a fairly early point having what we would think of as an America-like culture of mass convenience. And by early, I mean from a date where actual rural landlords in Bavaria were trying to pretend they still owned their tenants.
So yeah, my crazy idea is crazy. But is it possible, mechanically? At what point do automobiles become sophisticated enough that attachable and detachable engines would be feasible? Would someone actually think of something like this in the early days of automobile travel, while horses are still lumbering about, dropping piles of manure on the cobblestones? Don't be afraid to break it all down for me really simplistically, I was an English major, and it can be assumed with respect to car mechanics that I know nothing.