Alivox on Transit

The need for transit alternatives to the automobile has never been greater, and yet none of the choices has proven popular or effective. This essay describes a new idea - not original to me - that I call the InterBahn. The InterBahn is not "Mass Transit", since you don't share the ride with strangers. Nor is it "Personal Rapid Transit", since what's being transported is a vehicle, not a person. So let's call it "Vehicular Mass Transit", or VMT.

In brief, the InterBahn is a network of light metal tracks like those for modern roller coasters, except they completely enclose the cars within four rails, forming an open square tube. Within these tracks, cars travel silently at high speed under computer control, driven by electric motors. Routing is effected by the cars, which grip and release diverging and converging tracks - the tracks themselves never move.

Empty cars wait for you at stations, and will go directly to your destination, so the InterBahn is much faster than current mass transit, where you wait for the bus or train at the station and then wait again while it stops at other stations. And you don't have to share a car with a menacing stranger or a screaming kid. In that sense, it's more like a taxi.

In addition to these taxis, the InterBahn can move normal private street cars either on a car carrier or outfitted with an InterBahn chassis (stock or add-on). While on the InterBahn, cars don't use their wheels, gas engines, or normal controls, but they can recharge their batteries from the InterBahn track. This means that people can drive an electric car from their driveway to the nearest InterBahn ramp, then watch TV as the car recharges during their commute. For modern low-density cities, this means we don't have to build a station within walking distance of every home, nor a parking lot at each station.

Cars don't have to leave the InterBahn at your destination, either. Normally, they would pull into an InterBahn station: a series of short side tracks with platforms alongside. After you get out of your car, the InterBahn will park it somewhere else automatically, and you can call for it when you need it again, even at a different station! Cargo can also move around the InterBahn without a driver - think pizza delivery or even mobile pizza kitchens or other mobile stores.

And, like the Internet, the whole thing can be built piecemeal by independent agents, with no greater authority than a standard. Buildings will connect to the InterBahn and build stations to attract tenants, and automakers will build InterBahn chasses into their cars to attract customers. Trackbuilders will build track to earn fares from each car that passes, and to sell electricity. Parking lots will be built to attract fees from parked cars, as they are today. And cities will pass enabling legislation to solve their traffic and transit problems.

How it works Why it works Where it works

How it works top

This is a section diagram of an InterBahn track. The track itself is marked in black: it's a square tube 4m across (about 13 ft). In the four corners are the four rails, two of which carry positive electric current and the other two negative.

Holding on to the rails are eight wheel bogies (gray). Each rail is gripped by two bogies on opposite sides of the rail, and each bogie has two wheels, for a total of 16 wheels at each end of a car, 32 wheels per car. The wheels are metal, coated to improve the grip and electrical connection and to reduce noise.

The bogies are mounted on frames on each end of the car (blue). Each of the four sides of a frame has a pantograph that moves in and out under control of screw-drive electric motors (green). These motors control whether the wheels grip the rails or pull away to let the rails go - only two at a time, of course! There's also an electric motor that drives the car while it's on the track.

The car sits between the frames, with 3m (10ft) between the rails. That's enough for the widest car, or even for a standard freight container (shown here, in red). All tracks are one-way only.

When a car comes to a fork in the track, its onboard nav system decides whether to go left or right. To go left, it lets go of the two righthand rails and follows the left ones as they diverge. In a few meters, new righthand rails appear, and the car grips them. To go right, the lefthand rails are dropped. A fork could also be up versus down, with the upper or lower pairs gripping. Since the track never moves, it's very strong, and cars following each other very closely can take different routes.

When two tracks merge, the same thing happens in reverse: two rails are let go until the new ones appear alongside. The difference is that merging also requires making sure there's no other car coming on the other track. Since speed is controlled by the software, the merge is handled automatically and safely, with little loss in speed.

Normally, InterBahn tracks occur in groups of four, six, nine or more, depending on how busy the route is. It's common for the tracks to form a grid of rows and columns, so they can fork and merge easily.

The result is a truss of tubes up to four stories high, sitting on top of a street (and replacing the street light and telephone poles). The truss lets light through, so the InterBahn doesn't darken the street below it or the buildings on either side, but it's still pretty ugly. Some tracks may be covered or enclosed, which makes them look like giant hamster trails. And even though the cars are running on electric power, they make a sound as they pass, just like cars on a street do.

Some cars are built for the InterBahn: they have no road wheels at all. Other cars are normal street cars which also have an InterBahn chassis, whether it came with the new car or was added later. But even cars with no InterBahn chassis can ride on the InterBahn, attached to a car carrier that's kind of an InterBahn ferry.

Is the InterBahn safe? Of course, accidents can happen: a building could fall over onto a track, or a passenger could jump out of a car while it was on the InterBahn. Or an InterBahn car or track could suffer a catastrophic mechanical failure. But those things all happen now, too, on regular roads. The Interbahn is much safer than road driving because it eliminates the single biggest cause of road accidents: bad driving.

Why it works top

Big ideas like the InterBahn don't stand or fail on the basis of technical issues, though there are many of them left to solve; they work if they make sense in the big picture. Let me walk you through a scenario illustrating the advantages of the InterBahn.

So what are the features of the InterBahn that make this scenario work?

Where it works top

I live half the year in Seattle, a city that has tripled in the last 30 years without a commensurate investment in infrastructure. So now we're in a transit crisis: traffic and parking are awful, there's no room for more highways and no money for anything. We have a couple of half-baked projects under construction, but our best hope for a comprehensive mass transit system like those in New York, Chicago, London or Paris - a monorail - just fell apart.

Seattle would be a great place to build the first InterBahn. Using existing right of way without losing it to current users makes a lot of sense here, where space is tight, and elevated metal track makes sense in an earthquake zone (where concrete and tunnels mean disaster). And Seattlites are enthusiastic early adopters and environmentally conscious.

I propose we start by building eight new InterBahn tracks on top of the Highway 520 floating bridge, which connects Seattle and Bellevue across Lake Washington. Drivers who are making that commute now would happily pay to have InterBahn chasses installed on their cars just to save the two hours a day they now spend for a 20-minute commute. From there, the InterBahn could expand at both ends above the highways, penetrating both cities like arteries, all the way down to capillaries in each neighborhood.

Here's what we need: technical standards, enabling legislation, and a broad consensus that this is the way to go. There are plenty of companies that would start building the rest just to get in on the ground floor.

The Bahn is on!

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