Why would small rail vehicles exist alongside cars & normal passenger trains in the near future? In this world rails run throughout cities for metros & every town has a rail connection outside of the smallest (<1000 people). While cars exist in a developed capacity already (this world is a continuation off the current one with a few bits of alternate history thrown in so that some things make more sense), what would cause small rail vehicles to replace about 20-50% of personnel cars? These small rail vehicles are for personal transport with size going from that of an SUV to that of a large van or small truck. These vehicles would run alongside regular passenger rail & cargo trains, with the passenger rail having frequent enough services that scheduling doesn't matter much or the distances mean traffic wouldn't be interrupted without very large amounts of rail vehicles. These vehicles are mostly privately owned but some are rented out by companies & the public transport operator.

(BTW this isn't supposed to be a "gadget-bahn" type deal where its just making worse trains for the sake of looking fancy)

  • $\begingroup$ Are those small rail vehicles operated by a person who owns it or operated by the public transport company / operator / provider? $\endgroup$ Jul 29, 2021 at 12:41
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    $\begingroup$ @JulianaKarasawaSouza these vehicles are mostly privately owned but some are rented out by companies & the public transport operator $\endgroup$
    – OT-64 SKOT
    Jul 29, 2021 at 13:03
  • $\begingroup$ Food for thought: You'd never replace that many cars because you can't efficiently replace the need for trucks. Without an excellent explanation for why shipping and distribution to individual businesses and residences converts to trains, there will always be the temptation to use the same infrastructure for personal vehicles. You can pull a truck off the road - you can't a train, unless there are ugly tracks everywhere you can imagine. E.G. how will a personal train be parked in front of a store? Just the complexity vs. asphalt seems daunting. $\endgroup$
    – JBH
    Jul 29, 2021 at 14:43
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    $\begingroup$ "Privately owned" is not necessarily the same as "in personal use". If we want personal rail vehicles to make sense, "rail parking" should be in close vicinity of people's residences. $\endgroup$
    – Alexander
    Jul 29, 2021 at 17:18
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    $\begingroup$ @RonJohn you are falling into the fallacy of one system having to replace everything. We don't even have that now. Rural folk drive fully framed rear wheel drive or 4WD trucks or full size SUVs which are simply a fancier body on aforementioned frames, 8-10 cylinder engines, many diesel. Cityfolk drive FWD or AWD short-chassis unibody cars and Mini SUVs that are unibody and short chassis, 4-6 cylinders or electric. $\endgroup$ Jul 29, 2021 at 23:40

7 Answers 7


Mini-trains can be routed more efficiently than a full passenger train in a large station network

Ever been on a subway / train with more carriages than people? Does that seem efficient?

A while ago I described this city to explain why a city could be hexagon based. My answer was that every house is always within x minutes walk of a subway station - so there's no need for cars. Because this limit makes a circle, and because of efficient circle packing, hexagons form.

If everyone is living in nice suburban housing that isn't particularly dense, and the primary mode of transport is a subway in the middle of your suburb, you have 1 subway station per, say, 1000 people. That's not a lot of customers outside of peak times, and a lot of routes if a traditional subway line was to service them. A city the size of New York would have 20 times as many subway stations (8419 stations instead of 472.), and probably 720 lines instead of 36.

So - small (or even private) subway carriages. You get in, pick your destination, and the rail network automatically directs just your carriage to it's destination. No need to lug 100 meters of train to haul 4 people.

At peak times, there's 30 mini-trains waiting at the station stretched along the platform. An app on your phone (or an info booth) directs you into, say carriage 16 of 30, which happens to be going to your exact final destination. Since people are registering their routes by querying in an app, the super computer has a few minutes warning to optimse the next set of mini trains to pull up at the station given the destinations of those waiting at the platform.

Full sized trains are still used between cities, or on exceptionally busy routes.

  • $\begingroup$ What about when the family and I need to go somewhere not served by the rail line (like my mother and sisters, who live out in the country? $\endgroup$
    – RonJohn
    Jul 29, 2021 at 21:04
  • $\begingroup$ @RonJohn. Some over land transport would need to exist, farmers need to get around their property, maintenance needs to get done on the rails, and the rail network needs expansion. So yes you could rent a vehicle, or get them to pick you up from the train station in theirs. But the inconvenience of that process and slow speed (theres no highway network) would lead to the rail network being eventually expanded if a village gets over a dozen people or so. $\endgroup$
    – Ash
    Jul 29, 2021 at 23:41
  • $\begingroup$ "Some over land transport would need to exist". That's not going to work, because the huge fixed costs of manufacturing requires high volume to keep costs relatively low. $\endgroup$
    – RonJohn
    Jul 30, 2021 at 0:03

Two Problems Have Been Solved!
The situation you're describing is terribly dangerous. Mixing small lightweight cars (2200 pounds) and huge goods trains (up to 219 million pounds) is not a good idea because trains take an awful long time to stop. Most drivers of cars are essentially careless at best or woefully untrained at worst. Train drivers are certified and generally require continuing education.

Your near future has solved two problems sufficiently well to allow a broad mixture of vehicles to travel safely on the rails.

Problem 1: Physical Infrastructure
Many mainlines around the world are double tracked, which generally allows for multiple trains to move in opposite directions. Some are quadruplicated which allows for more traffic and allows for differentiation based on speed or train type (goods vs passengers).

Your system shall have been upgraded to all lines being doubled at the minimum. Most mainlines shall have been upgraded to six tracks or even eight. Stacking of lines, by building bridgework on top of ground level tracks, can easily increase capacity to sixteen tracks. Trains can then be separated to run along the ground level tracks while small vehicles can run above on the bridgeway.

In addition, all lines will have many more points or switches along the way to allow for traffic to be shunted from track to another. Switches will be much closer together to accommodate the smaller vehicles.

All intersections between rail and road will have short accessways that will allow the vehicle to transition from rail to road operational modes and back again. These accessways will serve the same function as motorway on and off ramps. No large intersections will be at grade -- all but the least busy intersections will consist of bridges or short tunnels.

Problem 2: Intelligent Control Infrastructure
More tracks and more trains and the addition of cars, trucks, vans and busses on the rails will mean more headaches for train controllers. Typical control & signalling systems won't be able to keep up. In your system, the most advanced systems we currently have will all be replaced by a fully automated system of AI controllers that rely on vehicle GPS locators plus input from vehicle sensors. Most of the AI work is done at the local level -- in your own car or bus -- as it coordinates with the vehicles around it through the local and regional control systems. The AI will continue to be monitored and directed by well trained human controllers who have access to not only the computer data but also traffic cameras, hazard detectors, weather station monitors, etc.

Because rails limit the manoeuverability of smaller vehicles, the driver will relinquish basic control to the on board AI. She will still have to monitor the usual variables of speed and surrounding traffic and will have to be aware of her course & route plan and will have to be ready to adjust if a change in plan is required. The AI in coordination with the local controllers will manage & execute a vehicle's entry to or departure from the railway.


Reason #1: Your World is Going Green

Electric cars are considered better for the environment than gasoline cars. Best case scenario, they can be powered by renewable energy sources like wind and solar. Even in the worst case scenario where you are still burning fossil fuels to power them, large scale powerplants can implement much better carbon reduction methods thanks to operating at a larger scale than millions of little internal combustion engines can.

Unfortunately, electric cars need some rather exotic materials at very high volumes to be able to replace the internal combustion engine industry completely. Mainly: lithium for their batteries. At the world's current number of automobiles, we do not have enough known lithium reserves in the world to meet the need of replacing all of our cars with electric cars, but if you take batteries out of the equation, then it is much more doable.

By putting private electric vehicles on tracks, you are able to keep them running off of the city's environmentally conscious power grid while also eliminating the need for batteries. As for how near future this could, be: the city of New Orleans actually recognized the advantages of rail vehicles several years ago, and used this knowledge as motivation to restore its old system of streetcars (after many years of being out of use); so, now New Orleans uses streetcars in place of city busses in many areas. If a city like New Orleans where to expand their already existing rail system enough, it would make since for people to start taking advantage of the rails for private vehicles too.

enter image description here

Reason #2: Safer Self-Driving Cars

One of the biggest challenges for self-driving cars is making sure that they can see roads, intersections, etc. in all weather conditions. Rail vehicles however are much easier to program. Instead of needing to "see" things, in most cases, a rail vehicle just needs to follow the track; so, bad weather will never make it drift out of its lane. Things like speed limits, stop signs, etc. are also much easier for a rail vehicle since you can just feed that data to cars via the rails. Coming up to a stop sign that is covered by a tree? No problem, the track lets you know when you need to stop. With most of of the work your car needs to do now being fail-safed by the tracks. Self-driving cars would be much less likely to hurt someone.

If this safety margin proves large enough, it could even motivate governments to ban self-driving cars, but not self-driving street cars. In this case, the allure of being able to buy a self-driving street car could be enough to get people changing over from roads to tracks.

  • $\begingroup$ I live in New Orleans. The streetcars are great and everything, but I wouldn't want to walk four blocks in the POURING RAIN or SWELTERING HEAT (95F and 95% humidity) with arms full of groceries. That's why there are so many cars in that picture. $\endgroup$
    – RonJohn
    Jul 29, 2021 at 20:22
  • $\begingroup$ @RonJohn I'm not saying New Orleans is there yet... but what if the city expanded the tracks over the next few years so that they passed in front of your home? And what if they then let you install a split that went straight into your garage where you could park your own mini-street car? And what if the grocery store added tracks to their parking lot so you could just park your streetcar there like a normal car? My point was that New Orleans can be seen as a possible early model that exists today that could eventually transition into the OP's idea, not that it is already there. $\endgroup$
    – Nosajimiki
    Jul 29, 2021 at 20:34
  • $\begingroup$ #1 Two-lane city/neighborhood streets are much too narrow for both "independent" automobiles and rail cars. #2 Not enough flexibility. (We'd regularly pack the family and our stuff into the minivan and go on vacation, visit relatives in the country, etc. Or haul stuff around. Or evacuate before a hurricane.) $\endgroup$
    – RonJohn
    Jul 29, 2021 at 21:01
  • $\begingroup$ @RonJohn Looking at the photo, it seems ya'll have no qualms about driving normal cars over roads with tracks on them. Seems to me that cars and street cars could share the same lanes. You'd just need to make the streetcars fast enough to keep up with normal traffic... as for evacuating before a hurricane... well maybe New Orleans is not the best model city to start from. Maybe somewhere more reliant on public transit like New York would be better? But once enough cities start to do it, you could have rail-interstates develop, and eventually too few restrictions to matter to most people. $\endgroup$
    – Nosajimiki
    Jul 29, 2021 at 21:53
  • $\begingroup$ "You'd just need to make the streetcars fast enough to keep up with normal traffic..." But they have to slow down to let people embark/debark and turn (while cars can change lanes and then turn). $\endgroup$
    – RonJohn
    Jul 29, 2021 at 21:56

Future cars will have the ability to run on rails

enter image description here

Rail+road vehicles will have important advantage over road-only vehicles. They should be able to travel by computer-controlled, streamlined railways which would allow them to beat city gridlocks and traffic jams with ease. In the intercity travel, rail vehicles would be able to reach speeds that are not safe at all for public highways.


The geographical conditions make it difficult to build roads once a railway is present, therefore using the railway is often preferred because the network is more and better developed.

Once more small rail vehicles meet they can set up a temporary convoy, creating some efficiencies.

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    $\begingroup$ Railroads are pretty easy turn into roads. I've seen it done in a few places where they just covered up the old rails with asphalt and called it a day. The harder part is going in the other direction. Adding rails to an existing concreate or asphalt road means completely ripping the road up. $\endgroup$
    – Nosajimiki
    Jul 29, 2021 at 20:42

There are three changes needed

  1. Less road infrastructure. Maybe fewer lane-miles, maybe lighter bridges, other possibilities. Fundamentally it must be less convenient and more expensive to travel by road than presently.

    • Example: Perhaps the USA didn't undertake the monumental 1912-1916 grade-separation project in large cities, and subsequently didn't invest in the U.S. Highway system in the 1920s-30s nor the Interstate Highway system in the 1950s-1980s.
  2. Robotic Coupling, Computerized Dispatch, and Distributed Power. Today's freight trains have improved incrementally from 1880: Head end motive power and air brakes. It's cheap and effective, and current freight railways compete on price (not convenience). By comparison, urban passenger trains tend to use distributed power and dynamic braking. They compete on convenience (not price).

    Distributed-power freight trains with automated (robotic) coupling/decoupling is certainly possible. They would be more flexible and safer...but also more expensive. You must handwave away the expense.

    Once all vehicles on the network use predictable/reliable traction/braking systems, have safe/rapid coupling, and are all under automated control, then you effectively have self-switching vehicles. Your dispatching can mix and match vehicles into dynamic trains for distance travel, or sort them into safely-separated discrete vehicles for short hops. You can optimize the network operation for price, for convenience, or any other factor you wish.

  3. Organizational shift of railways from owner-operator to open-access. This shift has been underway in Europe for about 20 years. It involves quite a bit of standardization (like signals, path planning, and dispatching) and regulation.

    You need an infrastructure-only organization to fairly dispatch the system, and to oversee the vast increase of rail infrastructure needed. Freights tend to run about 80-100km/h intercity, much slower than passengers are generally willing to tolerate. You might need two side-by-side networks, one for slower freight and one for faster passenger, to keep adequate capacity in your system. Happily, you can have quadruple tracking in only 20-25m.


The valuable thing about a railroad is the right of way

That's why Rails to Trails exists: to prevent the abandoned right-of-way from being sectioned off, so it can be held in reserve for something really valuable in the future!

You typically have a 25 meter (80’) right of way, and regular railroad tracks take 4 meters (13’) per track, transit somewhat less. So if you are pushy, you have space for 6 tracks before we start using eminent domain to shave people's backyards.

So for regular railroad operation, you allocate 2 freight on the outside / 2 passenger on the inside, compatible, so they can borrow each other's same-direction track for overtakes). That takes 4.

We got really good at autonomous vehicles, and they use slightly different rails (not interchangeable, don't want to mix those). So 2 additional tracks for your modular vehicle system. That is workable. All vehicles travel at the same speed. They are either computer controlled with close following, or you lash up many vehicles into trains so they dispatch as one vehicle, or both.

I doubt they would work as personal vehicles. Rail requires very consistent maintenance of vehicles. So this would be best done as one or many agencies or companies all repairing to the same standard. Both wayside detectors and onboard fault analysis would be looking for anything that could derail a train. There would be maintenance intervals and condemning limits for everything. You really couldn't leave this kind of maintenance to citizens. They don't do PM, and can barely pass smog today.

Speed is the answer

People won't just leave their cars behind, they'll leave their Cessna's behind.

Once trackways and maintenance are to this level, speed becomes less of a threat to safety. The aerodynamic drag of high speed movement is largely solved by coupling cars into trains.

So you can get going pretty fast. 150 mph would be well within reach, and remember, with "first and last mile" shuttles (which are cars), your portal to portal trip time is quite good.


The remaining trick is carrying your stuff. That would be done with containerization. All your stuff goes into a standard container which clips into the vehicle.

Containers come in several sizes, from suitcases to the size of a Sprinter van. There are train modules to fit each one.

There are "last mile" services much like DoorDash or Uber today, which will get your container from your house to the rail station, and from the destination rail station to your destination. They'll do the same for you as well.

Say you're an plumbing contractor who's going to Flint MI to fix bad pipes. You have a container with all your tools and supplies. You call for an Uber, the Uber shows up, grabs your container, grabs you and your apprentice, and off you go to the train station where you and the container get on a truck-module. Whoosh, through the system you go. At the Flint train station, another Uber shows up and takes your container to the job site. End of the day, another Uber takes it to secure storage and you to a hotel.


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