Caravan Train
 

An interesting idea for something you could see in the game

https://www.youtube.com/watch?v=mkpCzp0CmjY

https://www.youtube.com/watch?v=PMWBPrFVwLk

Many years ago if I remember, there was a mention in some thread about using trucks in place of locomotives, to haul freight wagons.
I think the thread was generally about restoring the rail network in small, local sections e.g. to supply fuel to power stations, move farm produce etc. etc.

4x4s have been used in RL as road-rail vehicles or even converted to haul small trains.

Here in Australia we have quite a number of 4x4s converted in such a way, the railways use them as inspection vehicles. Plus they have some larger vehicles (I think they're 2-4 tonne types) used as workshop vehicles for repair crews.
Works out better/cheaper when you considered that a good portion of the rail lines are in uninhabited regions and the inspection/repair crews may have to travel by road to get to the nearest town.

In World War 2, jeeps were fitted with flanged wheels to run on rail. The heaviest consist I'm aware of being pulled by one was a 52-ton train in the Philippines, which was hauled at 20 miles per hour. Not bad for a vehicle with a 1000-pound cargo capacity.

Modern road-rail vehicles tend to be more easily convertible between modes than the jeeps were.

Two weeks ago Aries Rail was testing a 20-tonne road-rail vehicle.

That's pretty damned interesting. Obviously rails can support the weight and there's been a number of armoured cars converted to rail use that were plenty heavy but this is the first time I've heard of such a large truck being converted for such use.
Even more interesting because the company doing this is in my home town and I'll take a wild guess and speculate that this conversion is probably aimed at the private railways serving the mining industry. They operate in some very remote areas with lengths of track running for many hundreds of kilometres through uninhabited countryside in some cases. In those regions, bulk ore trains are typically 2,400 metres long and "specials" can be up to 7,300 metres long so a couple of light utility trucks and a two-tonner probably just aren't up to the task!

TV show "Alaska Rail Road" has shown a few times where they use a converted cargo tuck (with knuckle boom) that drops large items for "homesteaders".