Jen & Elwood/Flickr

But the podcar concept will live on in the form of compact driverless vehicles.

The Mineta Transportation Institute just released a massive comprehensive report on "Automated Transit Networks"—more commonly known as personal rapid transit, and more casually known as podcars. Whatever their name, these systems use on-demand pods and exclusive guideways to combine the advantages of private vehicles with those of rail transit. But while the Mineta report considers the future prospects of podcars, it's equally appropriate to wonder if they really have one.

At least as they're currently conceived, they probably don't. Though the concept has been around for half a century, only five completed systems in the world can be reasonably defined as personal rapid transit: those in Morgantown, West Virginia, which opened in 1975; Rotterdam in The Netherlands (1999); Masdar City in Abu Dhabi (2010); Heathrow Airport in London (2011); and Suncheon Bay in South Korea (2014). While there's been a noticeable uptick in the past 15 years, four projects in that span is still, in the report's own words, "not enough to claim that there is an active market sufficient to support an industry."

That's especially true if you consider that four of the systems hardly qualify as full-fledged. The podcars in Masdar and Suncheon are really just shuttles at the moment. The one in Rotterdam is a feeder that links suburban offices to a rail station on a guideway that isn't even exclusive all the way. And the one in Heathrow is basically an alternative to an airport people mover. Other proposals and plans have surfaced in this time—an elevated podcar system in Tel Aviv being the latest—but nothing has come of them.

The most impressive personal rapid transit system to date is the one built (as a government-funded experiment) on the West Virginia University campus in Morgantown back in the 1970s. The Morgantown PRT reaches five stations on more than eight miles of dedicated track, with pods that each seat eight people. Riders indicate their destination, and the pod can skip intermediary stops to get there (though during off-peak hours it waits a few minutes for others going to the same place). During the school year, some 15,000 people ride each day.

(Sean_Marshall/Flickr)

The Morgantown system shows the promise of personal rapid transit, and probably explains why the idea has hung around for so long despite rarely being realized. Transit advocates like it because such systems have the potential to reduce car reliance in cities. Transit opponents like it, too, because the on-demand service, relatively private pods, and direct-to-destination trips kind of make it public transportation without the whole bothersome public thing.

Upon closer inspection, it's this attempt to be everything to everyone that creates some problems for personal rapid transit. As more people use the system, it becomes less able to accommodate individual demand for destinations, which renders it more of a traditional rail transit system—but without enough capacity to handle rush-hour crowds. Meanwhile, the direct-to-destination element still can't beat the door-to-door service offered by taxi networks. In other words, personal rapid transit reproduces modes that already exist in the city, only less effectively.

For all that, cities still take on significant costs. Mineta estimates a cost of $10 million to $20 million per elevated mile for a medium-capacity personal rapid transit system (below). Only a handful of companies "can credibly deliver" a system within a few years, according to the report, and it's hard to see any of them being realized "without public intervention." Factor in the inevitable cost overruns of mega-projects, and podcars become a drain on precious transit resources without providing all of transit's benefits.

(Mineta Transportation Institute)

Then there's the problem of integrating such systems into the existing urban landscape. Between the need to dedicate lanes to high-capacity transit, create space for cyclists and walkers, and reduce road capacity overall where possible, there's just not much room for new low-capacity fixed systems on city streets. That leaves elevated podcar systems, which opens up a world of complexity with existing city infrastructure—exemplified by an awkward image in the Mineta report showing a PRT line blasting through sidewalk trees above the heads of pedestrians:

That's the elevated podcar up there—in the tree above the pedestrian's head. (Mineta Transportation Institute)

There are some situations where personal rapid transit seems like a reasonable option: distinct areas like airports or neighborhoods, or perhaps small-to-medium sized cities (Mineta suggests those with populations under 250,000) without mature transit networks. Cities like Masdar, being built from scratch to discourage private vehicles and road reliance from the get-go, are the ideal podcar canvas. Yonah Freemark summed up this potential best a couple years back:

For airports and new cities, PRT could supplement other mass transit systems rather effectively and encourage people to live car-free lifestyles by providing them destination-to-destination service with minimal walking to and from stations. In newly built environments, PRT could be constructed cheaply and it could be installed in such a way that does not disrupt its surroundings.

But there aren't many Masdars out there. And regardless, there's an even simpler reason why it's probably not going to happen for podcars: driverless cars. Once autonomous vehicles learn to navigate cities, they will offer every advantage of personal rapid transit without any of the limitations. In fact, cities that might once have deployed personal rapid transit have already turned to driverless cars, from Ann Arbor, Michigan, to Milton Keynes in the United Kingdom. An era of shared autonomous taxis is not far off.

Then again, the driverless cars of the future might look a lot like the podcars of the past. Just take a look at the autonomous car prototype released by Google in May: it's as cute, compact, and geometrically similar as the personal rapid transit pods that zip around Morgantown. It's not a stretch to see them as conceptual cousins, with one capable of roaming the open roads while one is confined to closed tracks.

So there might a future for podcars after all—it just isn't the one initially envisioned.

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