Tuesday, July 26, 2011
In the early days of PRT, back when governments and multinational companies were first eyeing the idea, the whole concept was so futuristic that it was plenty enough to envision a standard vehicle, track and station and multiply them around into a grid, and call it a system. Back then it was a question of whether those new computers were capable of reliably and safely managing traffic flows. As I was introduced to the concept, there would be a station every block or so, so that it would not be too long of a walk to get to one. The track would be one-way and you could get anywhere by circling around. Thinking back, maybe this just wasn’t good enough, and nobody realized it.
Personally, I have had a very hard time trying to shoehorn the cities I know into such a scheme. It would be great if the funds were there to actually make such a comprehensive grid, but since they are not, it becomes a question of giving the most bang for the buck. But the systems that were designed for the grid model may not exactly fit the new roles. Moving away from a grid model has implications for the track, the vehicles, and the stations.
Here are some typical situations that may exist outside of any downtown grid; The freeway commute - this calls for a relatively fast vehicle and outlying stations with lots of parking. The “strip”- This is where eateries and retailers have reached a critical mass so that the whole stretch of road has become like one long mall. It probably would call for two-way track that does not interfere with signs and driveways. Stations should be minimal footprint, perhaps designed specifically for private property, such as in the parking lot of a major retailer. Major destinations – Areas such as a museum district, a major hospital complex, or stadium need access to the system, although there may not be enough in the budget to put stations every half mile between them and other destinations. These call for large stations and a system with distributed automobile parking, since it is unknown where a visitor’s origin is, but it is likely that the first leg of the journey was from outside the system.
I think that each of these scenarios is extremely typical and each plays to the strengths or weaknesses of a given system design. True, these introduce design complexities that are much greater than what a PRT company would ideally want to tackle. But what is the choice? Try to interest cities in a “one-size-fits-all” system?
In the end it is each city’s specific layout that must be addressed. Perhaps rather than a grid mentality, what is called for is a destination mentality. How can the most important destinations be served with the least amount of track and stations? That, after all, would seem be the best value proposition from the city’s standpoint. Yeah, I know... None of this really plays to PRT’s strengths. But PRT track is also cheaper and less disruptive to install, and being raised so as not to block crossing traffic is a huge bonus. So perhaps PRT can prove itself with less track and stations than the network we would like to see.
A couple of points: First, parking. It seems pretty obvious that most people will have to park their cars to use the system. Maybe there are a few older cities out there that are teaming with pedestrians who live very close in. But for most of us, the construction of arterial highways has created a suburban landscape of car dependent homeowners and apartment dwellers. This calls for assessing each of the out-lying station’s potential to be a gateway to the system, and therefore a place to store the car in the meantime. Will merchants be willing to share parking in exchange for being convenient to the riders? Probably not in areas where people would want to park for the whole workday. Bottom line – Any system will need sufficient parking to support enough passengers to make the system viable. That potentially means thousands of parking spaces. It is likely that some stations will essentially be parking lots. Land costs are not inconsequential, so parking ends up becoming a factor in routing.
Another point is that in a landscape of very limited funding, shuttles (GRT) must be reconsidered. If the system is centered around serving the most important destinations, then it stands to reason that more people will be sharing a common itinerary. This has implications for track size, although we must avoid anything too big to be visually acceptable. The track I have shown in previous posts is about as big as I would want to risk. I think it is noteworthy, though, that technologically it is a simple matter to keep heavier vehicles spaced further apart than lighter ones to minimize weight concentrations on the track. I would keep it under six passengers anyway. Such vehicles would simply share track with the PRT vehicles and move between high capacity stations. These would be “express” shuttles, so if your destination isn’t a main terminal, you would use PRT, which could service all destinations.
A last point about stations. I have opted for a suspended design mostly because such a system can drop to ground level and ascend with a minimum of station related hardware and track. Neither long ramps nor elevators are required, which is of paramount importance in a stripped down, budget starter system. A suspended system would also seem ideal for parking lots since PRT vehicles could go directly to your car yet there would be no track to cross.
In a “destination oriented” design, the point would be to enable the rider to eliminate the lion’s share of driving from his/her day-to-day routine. The idea is to make all of one’s normal destinations available and convenient to the rider – shopping, dining, entertainment, etc. A well thought-out system could provide traffic relief that would ripple throughout the city’s side streets, not just the roads that parallel the track. This is because it would cut out what would otherwise be individual outings in the car. A few choice stations, (and some very lucky merchants!) would make most driving unneccessary. Also, I cannot help but consider such a proposition from a tourism point of view. To some cities this is a very big deal. And, being elevated, it’s naturally scenic!
So how stripped down could a system be? I guess I can imagine a single convoluted loop as a starter, but every city is different. Finally, I would add that there MUST be a way to branch track without a long shutdown. Any prospect of skipping over areas can only be temporary. Success will mean a demand for stations all along the track, so adding stations must be easy to do. I posted a design for a branchable box-beam track in post 71.