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The RoBlog
Saturday, October 23, 2004
 
SkyWeb Express Personal Rapid Transit
One of the most interesting things I've seen in a while is Taxi2000's SkyWeb Express concept. The basic idea is that instead of busses or commuter trains, there are little single to triple passenger vehicles that run on an elevated track (track is a bad description of it, they call it a Guideway, but once you see it, you'll understand what it is).

You get in and tell the vehicle which stop you want, and it leaves the station and goes directly to your destination station without stopping at any other station. To stop at a station, the vehicle essentially pulls off of the main line, and since only those vehicles stopping at a station have to pull over, everyone else continues right along.

Frankly, I'm surprised this hasn't come into existence yet. Apparently it's been around in some form since at least the '60s.

Below is the link to the videos section where the most bang for the buck can be had. It is worth exploring the rest of the site as well, as the writing is clear and the site structure makes for sensible, easy reading.

SkyWeb Express Personal Rapid Transit - A revolution in urban transportation: SkyWeb Express & PRT Videos

Below is some spewed notes I took as I wandered through the site. You may see these more in future entries. I'll try to keep the interesting (and coherent) things above any links to a site, and my ramblings below it so you can ignore them if you like.

Nice attempt to tackle some of the major complaints about mass transit:

What if someone in the car ahead of you in the station is taking a long time or breaks down in the station?
There could be docking bays where a car separates from the main station track into a Y shaped section. For example, they come in on the right leg of the Y, and pull into the base. People get off in one direction and board from the opposite side. Once the new passengers are aboard, the door closes, and the car essentially drives in reverse down the left leg of the Y, rejoining traffic. The portion of the car above the rail could rotate during merge so passengers are always facing front. This assumes that the car's motor can travel equally well both forward and backward. If this was not the case, but the car could still travel backwards to some degree, you could eliminate the left leg of the Y and have the car reverse back down the right leg of the Y (the central system slowing or stopping oncoming cars as necessary) and then go forward again on the main line. In either case, people that take a long time to load (elderly or handicapped, people carrying bags or packages, or the like) will not adversely effect the ability of other passengers to arrive and depart.

What if the car in front of you breaks down both in the station or on the track?
For people not already on the same segment of track, cars could be routed around the breakdown (assuming there are other routes to all destinations). Similarly (again, assuming alternate routes to all destinations), cars behind the breakdown might be backed up and switched to another section of track. If the system is centrally controlled, oncoming traffic could be slowed or halted to allow for a back-up entry.

Could long lines leading into a station lead to backups on the main track?
Seems like you'd just try to plan for as long a queuing line as is needed.

So, what are the downsides of the system?


Why do they not talk about longer-haul trips? At 40MPH, trips of many miles are possible (e.g. Vancouver, WA to downtown PDX), yet they talk only of downtown and feeder coverage.
Comments:
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I'm involved in the PRT community and manage a couple of web pages devoted to the field. I'd like to offer some comments and corrections on your excellent posting.

"What if someone in the car ahead of you in the station is taking a long time or breaks down in the station?

There could be docking bays where a car separates from the main station track into a Y shaped section.
"

It is not anticipated that individual delays will be a problem. First, most stations will have multiple bays. Second, boarding is made as simple and fast as possible--payment and route selection occurs before boarding, and the design must make ADA/wheelchair access as easy as it is for the fully-able-bodied.

"What if the car in front of you breaks down both in the station or on the track? For people not already on the same segment of track, cars could be routed around the breakdown (assuming there are other routes to all destinations). Similarly..."

This is pretty much spot-on. In addition, under the Skyweb system a breakdown is pushed to the repair center by the next vehicle. Generally, Skyweb is designed with few moving parts to break, as well as redundancy throughout, making the odds of unplanned stoppage literally astronomically low.

"Could long lines leading into a station lead to backups on the main track?

Seems like you'd just try to plan for as long a queuing line as is needed."


Actually, there are primarily three factors: the demand for each station in terms of arrivals AND departures, the number of berths per station, and the size of each "loop" or circuit of elevated track.
Demand: PRT spreads-out demand per station by having many small stations close together (ideally 1/2 mile apart).
Berths: Most stations will have 3 berths. In busy places (downtowns, stadiums, airports, intermodal transit stations) stations would be scaled-up by adding more berths (major station cost is the elevator and trip selection "ATM", marginal cost of each additional berth is relatively low).
Loop size: In the rare (see Demand) event of a station and its approach siding being full, a car can be "waved off" and directed to go around the local loop and re-approach. The ideal size of a loop is 1/2 mile on a side for a total of two miles; traveling this at 40 mph takes only 3 minutes.

"Would computer controlled cars compete in the longer term?"

It depends what effect you think Time might have on PRT's effectiveness. Urban densification and suburban expansion are not a problem for PRT, as the system scales-up well.

"Would be nice to have some sort of wireless networking capability for business travelers."

No reason a community couldn't specify this as an amenity.

"Why do you have to type in a destination number? Would be nice to have alternatives, like a web service :) that you can interact with where you tell it your destination and it figures out the number."

To be true public transit the system needs to accommodate the cash-paying customer--thus a system map, showing You Are Here and stations with numbers. But there is no reason you couldn't in addition have a web-based account tied to a SmartCard or RFID device-- or even a cellphone or Blackberry. And PRT designers have thought of these and other possibilities and are planning for them.

"Skyweb claims to have a lower startup cost than other large transportation infrastructures (e.g. Light Rail)"

Yes! Engineers say that the lighter-per-foot something is, the cheaper it is to fabricate and install. PRT is extremely lightweight relative to trains and monorails.


"* Doesn't meet commuter throughput claims"

How? Remember, station demand is distributed/spread-out. In addition, routing is spread-out too. The "mesh" configuration of the network means there is more than one way to get from A to B, especially if they are far apart. If one PRT track can handle 7200 vehicles per hour (30 mph, 22 ft headway), imagine what multiple parallel tracks can carry.

"* Realestate for stations"

Land does cost money, but the idea is to keep stations small so it is easier to find space without tearing down any buildings or trees. A Skyweb 3-berth station is approx. 30 feet long by 12-15 feet deep, smaller than a house. Ideal locations would be existing public right of way and public buildings like police and fire stations, libraries and schools (already frequent destinations). Stations can also be built into new or remodeled buildings.

"Why do they not talk about longer-haul trips? At 40MPH, trips of many miles are possible (e.g. Vancouver, WA to downtown PDX), yet they talk only of downtown and feeder coverage."

Downtown and feeder service is planned for the near term, because PRT doesn't want to bite off too much too soon. But that doesn't mean to exclude near-term short-mileage links such as Minneapolis-St Paul, Seattle-Bellevue, or Vancouver-Portland. Furthermore, faster speeds are possible for Skyweb (up to 80 mph), and the maglev Unimodal (not yet ADA compliant) plans top speed of 100-120 mph immediately.
 
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Thanks for the comment!

My response is here.
 
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I agree that starting cost would be high, but I don't believe operating costs would be a problem. Not having to buy drivers or fuel, I have a hard time seeing them have a hard time to operate at a profit.
 
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