Posts about PRT
Personal Rapid Transit, or PRT, proposes to duplicate city street networks with new redundant elevated street networks for shared cars. It gets a lot of press, but after about 60 years of trying, has not yet been successfully implemented.
The United States tried it once, in Morgantown, WV, in the 1970s. I've always been curious about the system, so when I passed through Morgantown last weekend I stopped to check out the PRT.
What I found was cool, but couldn't be called "PRT" by any reasonable definition. The system consists of a single route (PDF) with no deviations, and when I rode on Saturday, trams came according to a schedule and stopped at every station along the route.
There were bypass tracks around each station, so I assume the technical ability exists for trams to skip intermediate stops and go directly between any two destinations along the line, but what I experienced was absolutely no different from any elevated transit line in the world, except that the vehicles were smaller.
In the grand debate over PRT, I suppose you might call me a moderate. I don't think the sort of elevated systems traditionally envisioned are worth the expense of literally duplicating our street network, but I do think low-tech ideas that make use of our existing street infrastructure could have value. What is Capital Bikeshare, after all, except a low-tech, on-street version of PRT?
Enjoy these pictures from Morgantown.
Cross-posted at BeyondDC.
Last week, Steve Offutt introduced the last mile problem in Tysons Corner. With the Metro on the way, a solution is clearly needed to get transit riders to their apartments and offices.
I suggested that a system of busways could easily speed circulators around the neighborhood. Steve countered with a proposal for a Personal Rapid Transit (PRT) system spanning the area.
The series has generated a lively discussion, and that's important. I'm skeptical of the ability of PRT to succeed or gain acceptance because of PRT's capacity problems, its removing pedestrians from the streets, and the visual impact.
To compare Tysons with PRT and other transit systems, I've overlaid Tysons with to-scale representations of PRT and heavy rail transit in other cities.
Detroit and Miami both have circular people movers designed to transport people around their central business districts. Detroit's is mono-directional; Miami's is made up of three "loops". Also included is an overlay showing the downtown Washington Metro stops to-scale over Tysons.
The experience of this region over the last thirty years shows that transit can reshape our urban areas. But more important than the form of the transit are the policies shaping land use. The District, Arlington, and Montgomery County enacted policies to encourage transit-supportive densities and uses. As a result, urban villages dot many of their station areas. On the other hand, all the transit in the world wouldn't help a jurisdiction with no desire to rethink the areas around Metro stops.
PRT in Tysons is not the right fit because it will not be the right kind of transformative catalyst. It will not create the pedestrian density that is a vital part of a vibrant urban area. The sidewalks around Rosslyn, Ballston, Bethesda, and Farragut Square are all crowded, especially with commuters during rush hours. The ULTra PRT system called for by Steve would rob the areas around the Tysons stations of that vibrancy.
Workers would not need to walk to the office. Instead, a futuristic pod would drop them off right in their building's lobby. While this might be convenient, it would seem to obviate the need to change Tysons. Sidewalks and shops would be robbed of their users, and the area would remain disjointed, even though it would be connected by a transit system fit for La Ville Radieuse. My concerns also extend to the viability of the mode. After all, if one extends PRT to its logical conclusion, one approaches the medium known as the "car". The PRT concept basically entails a guideway running along every street, no waiting, no unwanted intermediate stops, no unwanted travel companions, and door-to-door service.
That formula hasn't created the livable spaces we are seeking today. And it also presents the question of congestion. If Tysons' road network is already overwhelmed with personal vehicles, how would a system of individual personal pod-vehicles making the same trips be immune?
Besides, Tysonians would never stand for the miles of elevated guideways. The fight to bury the Silver Line is an excellent example of how Tysons' civic leaders would react to this PRT proposal. Instead of a linear line or perhaps a circular loop, the ULTra concept would weave a web of elevated tracks with stations on almost every block. I doubt the system could be built without serious objections about aesthetics.
Another logistical hurdle seems to exist for a Tysons PRT. While PRT might be a great concept for a place with many diffuse origins and destinations, the reality is that Tysons won't work that way. Instead, there will be four main origins located at the Metro stations and diffuse destinations. Passengers will arrive in waves every 3 to 6 minutes as each Metro train stops.
ULTra's design does not seem to be prepared for waves of passengers arriving all at once. Cars can only carry up to 4 people each and have only one door per side. The makers claim each berth in a station can handle 400 departing persons in an hour, or about 6.5 per minute. That means it would take 14 berths just to handle the capacity of a Metro escalator, which can discharge 90 people per minute.
If we're going to clutter the Tysons landscape with elevated guideways, we could get a bigger bang for our buck with an automated circulator like Miami's or Detroit's. These systems use larger vehicles and stations, but they have a higher capacity. Like heavy and light rail, they can be coupled into trains. They have multiple doors and plenty of seats and standing room. Vancouver's completely automated subway system, SkyTrain, just transported 577,000 passengers per day on average during the Olympics, well over its usual average of 334,000. And like PRT, automated guideway trains can run at high frequencies with low labor costs.
Unlike PRT, automated guideway systems have shown they work with high volumes. The world's busiest automated line carries 175,000 a day on a 1.1 mile route with 6 stations in the Atlanta Airport. Even if guideways for a heavier duty automated circulator cost more, building less of them (compared to PRT) could present a cost savings.
I still think that a cheaper, at-grade system of dedicated busways or streetcar lines could serve the area just as well with a much cheaper pricetag.
The reality of the situation is that Fairfax County has little money to spend on any secondary transit system in Tysons, and even if a last mile system was ready to open when the Silver Line opens, there would still be a long way to go. And Tysons will be a challenge to serve regardless of which mode is used for its last mile system.
Regardless of our method, all our transit investment will be in vain if Fairfax leaders don't stay committed to transforming Tysons. But that doesn't mean Tysons can skip the last mile system. Indeed, with the vast distances separating Tysons' spaces, a supplemental "last mile" system is absolutely essential. And it is also essential that we get it right, otherwise a revitalized, transformed Tysons will still find mobility obstacles hampering its growth for many years.
A bolder proposal, for Personal Rapid Transit (PRT), generated considerable controversy among the GGW contributors over email. There is a range of opinions on this technology among the contributors as among planners in general and the public. Therefore, Steve has put together a piece arguing for it, and Matt wrote a counterpoint which we'll post next.
Instead of waiting until Tysons' very long term fixed-guideway transit, Tysons could become a visionary community by building and implementing a state-of-the-art PRT system at the beginning.
At least one company has developed a proposed plan for how PRT might be deployed in Tysons. For those of you unfamiliar with the debate on PRT, there are very strong opinions on both sides about this technology, ranging from fairy tale to rapture. Personally, I believe the reality is somewhere in between.
The big advantages of PRT are that waiting times are very short and all travel is direct. There's no need to stop for other passengers to get on and off, no transfers, and one-seat rides to all destinations. If PRT works as advertised, then one could travel from a Metro station to their destination a mile or so away in 3-4 minutes rather than the 12-15 it might take with a circulator. It would also function much better for moving around within Tysons, which is currently laborious by any mode.
For comparison, Fairfax estimates the circulators would cost $9 million to purchase and about $5.8 million per year to operate. That would be $67 million for ten years, $125 million for 20, without accounting for replacement buses.
Cost estimates for PRT range from $7-15 million per mile, with Tysons on the higher end due to its already developed land. Because of the reduced weight and footprint of PRT systems, they cost significantly less per mile than other rail systems such as streetcars or light rail. The green loop shown in the PRT proposal cited above is about 4 miles of guideway, so approximately $60 million. All three loops look to be about 14 miles of guideway, or a total of $210 million. A company representative I spoke with believes revenues from fares can cover operating costs.
A potential source of investment is from developers. West Company owns about 10% of all the land in Tysons, but it's mostly out of walking distance from the Metro stops. If that property were made much more easily accessible, the property value would significantly increase. Perhaps they would be willing to help fund the costs. Hotels might pay for track sections and stations that directly serve their properties.
Of course, developers could fund any mode, not just PRT. However, I don't believe land owners would invest much in circulator buses compared to some sort of permanent infrastructure.
Is it risky to get out in front with a new technology like this? Of course. But streetcars are essentially 19th-century technology; PRT is 21st century technology. The technology has advanced enough that an entire city in the UAE, Masdar, is being built with PRT as its primary form of transportation.
Heathrow Airport in London will have the first operational, albeit modest sized, system in the next few weeks. Making PRT work in Tysons would not only solve the last-mile problem, it would expand the value of the Silver Line to the entirety of Tysons, and the system itself would make Tysons a destination in its own right, attracting additional visitors and investors alike.
- Bikeshare is a gateway to private biking, not competition
- Judge denies injunction against closing schools
- Long-term closures: A solution to single-tracking?
- Metro policy for refunds after delays falls short, riders say
- M Street cycle track keeps improving, draws church anger
- PG planners propose bold new smart growth future
- Prince George's County struggles to get trails right