If you thought Smart cars were goofy before, wait until you see one that thinks it's a train.

In what it calls "a light-hearted, one-off experiment," Smart worked with train engineering outfit Interfleet to adapt a Forfour model for life on the rails. That meant ditching the wheels and tires in favor of 22-inch steel wheels that weigh 176 pounds apiece. Riding the rails eliminates the need to steer, so the team disconnected the steering and welded aluminum supports between the axles to lock everything in position.

The end result is the "Forrail," which zipped along the privately operated Bluebell Railway in Sussex, England, during a model train show last weekend. After running the "fully certified mini-train" on 10 miles of track, the team converted the car back to its original, road-going state.

As silly as this may seem, the idea isn't new. Road-rail vehicles, which use small steel wheels in addition to conventional tires, usually are used for things like track maintenance (and exploring Mexico's rusting railroads)—not the kind of work a Smart excels at.

Smart says the experiment was designed to explore whether the convenience of rail travel—no congestion, a clear path to your destination—could be combined with the upsides of the car. It's more PR stunt than serious idea. There's no indication Smart is serious, and specifically says it does "not encourage any individual to carry out similar modifications. It’s incredibly difficult."

Mercedes-Benz

But this unusual project has less in common with road-rail vehicles than it does with "personalized rapid transit," which combines public transit with small, private pods. "There's this dream of having the right of way to yourself," says Sarah Kaufman, adjunct assistant professor of planning at New York University, "because cars on the road have to battle congestion caused by other cars."

The idea's been around for decades. The ULTra (Urban Light Transit) system at London Heathrow Airport is a rare example of a working system. Since 2011, it's shuttled hundreds of thousands of passengers between one terminal and a parking lot. Morgantown Personal Rapid Transit is another example; it moves people between five West Virginia University campuses. Far more have failed however, including projects in Paris, Germany, Japan, and Illinois.

Last year, the Mineta Transportation Institute wrote in a report that PRT "does not appear 'on the radar' of urban planners, transit professionals, or policy makers when it comes to designing solutions for current transit problems in urban areas for a variety of technological, financial, and political reasons." Namely, they're complicated and costly to build.

So no, hacking Smart cars to run on rails is not something to be taken seriously. First off, the idea of and asking drivers to swap between regular wheels and nearly 200-pound steel substitutes is amusingly unworkable. Also, it would be a waste of useful track infrastructure, says Paul Supawanich, a transportation planner at Remix, a startup that works with transit agencies.

There is a burgeoning movement towards personalized transit. And I think that will go hand in hand with automated vehicles. Sarah Kaufman, adjunct assistant professor of planning at NYU

The benefit of rail is that it allows huge, enormously heavy vehicles to move around, without congestion. Putting a Smart car—which is both light and carries at most four people—on tracks is "using this very cost-intensive, heavy-duty infrastructure for a very low return," Supawanich says. The infrastructure is better used for trains.

What's funny about this project—and let's be clear, Smart isn't talking about doing this seriously—is it's an unexpectedly anachronistic idea from a brand that's part of Daimler, which is working hard on autonomous technology for tractor trailers and Mercedes-Benz passenger cars. Because the advantages of PRT are coming, just not in pods that run on tracks. They're coming in self-driving cars.

"There is a burgeoning movement towards personalized transit. And I think that will go hand in hand with automated vehicles," Kaufman says. And they give us the upsides of a PRT system, what Supawanich calls the "magical win-win."

There are downsides, naturally: These cars enable sprawl, Supawanich points out, and don't answer the carbon emissions question (though they could easily be electric). If your key metric is moving people efficiently, getting everyone their own robo-lounge isn't the answer. The technology will also save lives and give us more time to work, talk to loved ones, or, more likely, get stinking good at Minecraft.

But we get the upsides of a PRT system, without major infrastructure development. Forget rails: Autonomous cars will work very much like a train, following one another, reducing congestion, and then peeling off individually and taking us straight to our homes. No steel wheels required.