a vehicle of density: why PRT is more than an iMac car

Posted by on May 19, 2009 in transportation, urban planning | 2 Comments


“mass transit… so hot right now…”

if you look at the perception of sustainable architecture today as opposed to 10 years ago there is a pretty remarkable shift. more and more there is less emphasis on off-the-grid cabins in bucolic landscapes and much more mixed-use projects and transit orient developments. the pastoral solar cottage as sustainable icon isn’t going anywhere, but as there is a collective realization of the scale of the problems sustainability needs to address, there is more focus on how architects can make cities themselves more green as opposed to isolated homes. as alex steffen wrote in worldchanging, “if you want to be green, live in a city.” the efficiency of having large masses of people in the same area to bring resources to will trump any sort of gains met by a wind-powered rural cabin, especially as we look to greening our society as a whole.

one of the main issues with sustainability on a city level is how the residents move around within it. unfortunately for many american cities, this is more of a planning issue than anything else. mass transit in a city with a dense central core like new york, philadelphia or seattle is much more successful than a more diffuse city like los angeles or phoenix.

image from wikipedia.org

the term Personal Rapid Transit sounds a little bit like an oxymoron or a desperate re-branding of the automobile by GM. while it sounds like “personal” would be referring to either the size or scale of the vehicle, it is more a reference to how the system works. the only built PRT system in morgantown, west virginia uses vehicles that are sized for 20 riders- but what makes it “personal” is that the riders collectively decide where the vehicle goes and that the cars are dispatched as needed. if the there are more riders at one station as opposed to another, the system sends the cars there and if the riders on a car aren’t heading to a specific stop the car bypasses it.

image from systematica through treehugger.

while the WVU system is interesting, it still only runs along a single line. this is a fairly conventional model of how we understand transit it to work- one line takes us a set of destinations where we can either use a different form of transportation or transfer to another line. but what is interesting about a networked or intelligent system is that it has the potential of breaking this model and creating a more facile one. a route is simply a conceptual machine to help a rider understand where that vehicle will take them, but if the rider were to tell the vehicle where they needed to go, the idea of a route would no longer be as important.

the remarkable flexibility of the system is why PRT could have the potential of working incredibly well in more spread out urban and suburban areas. urban planners and transportation designers frequently describe the biggest issue with mass transit is the problem of the last mile- mass transit can frequently take people from one general area to another general area well, but moving people within those areas is a challenge. but with a “personal” mass transit system, the possibility of people quickly and conveniently moving from their houses to a larger transit hub seems likely.

so what makes a PRT system different from the currently form of flexible, personal transportation (the car)? parking. aside from the implied emissions and energy usage improvements of electric vehicles, parking is a clear advantage of a PRT.

in an article titled “we paved paradise”, salon.com reported the effects that municipal parking requirements have had land use policy, the classic example being that a typical code for a restaurant would require five times as much space for parking than the actual restaurant. at one point I had been told (though I can’t seem to source it), that in LA there are five parking spots for every car. while the environmental effects of that many impermeable surfaces and that many heat islands is massive, the real problem is how more and more parking spots continue to spread out our cities more and more- making the need for parking more and more necessary.

this is where the PRT is a really compelling idea. in theory, PRTs are never parked. they either constantly move or shuffle themselves to the station that has the highest probability of needing a vehicle the soonest. so the energy efficient, non-emitting communal machines were already compelling enough to most environmental advocates, but reducing the need for automotive parking could not just provide a cleaner alternative but could begin to significantly alter the way our cities are organized. a more efficient, closer urban fabric is easier to navigate by foot or by bike, which reduces the need for an artificially powered vehicle to begin with- which is ultimately the most sustainable goal of all. more than energy efficiency and resource use, a vehicle that can act as an agent against suburban sparsity will ultimately reduce the needs for vehicles to begin with.

PRTs as a commonly used urban vehicle is still a long way off- but at the moment they provide a clear example of how the vehicles in which we choose to move ourselves can directly effect the space we inhabit. it’s not just about the energy our vehicles use- it’s all of the resources they demand that will determine if they are sustainable or not.

[youtube=http://www.youtube.com/watch?v=7PyUQuWmt2M ]

the future PRT system at heathrow airport

::ULTra’s construction photos of the heathrow system

::BBC news on heathrow’s PRT system

::a treehugger interview with luca guala with systematica on the PRT system at madsar city

::treehugger on PRTs in uppsala, sweden.