Saturday, January 3, 2009

14> Personal Rapid Transit and Streetlights

I heard, the other day, about a proposal whereby streetlights would be turned off to save energy but could be switched on by cell phone. Odd idea, but it gets the old mind working. I was mostly working in Tucson, AZ for the last few years, and they have a number of observatories near town, so they are keenly aware of what is called “light pollution.” I fly a lot, and have for many years, and I must say the brightness below is really getting out of hand. Remember a barrel of oil saved domestically is as good as a barrel of oil produced domestically. Energy is wealth, and the celestial glow of the city is the glow of would-be prosperity diffusing into space.

So how does this apply to PRT? Well let’s imagine the ideal street lighting. First, it wouldn’t blind you, so your eyes could see more with less of it. It would be more uniform, softer. It would shine away from you, not at you. It would be directed mostly toward important things like signs and curves in the road and blind driveways, If there was no one to see it, it would go out, or at least cut back. Intelligent street lighting is an idea whose time has come. PRT could be the platform and catalyst for that change. . This is just one more selling point to PRT that shouldn’t be ignored.


timote said...

I agree with your thoughts conceptually. Practically I'm not sure how PRT would help outside of, as drawn, the ability to have more lower wattage units rather than single big too-bright units would be wonderful. I don't remember the details, but I'm pretty sure the drop off is non-linear (cube of distance?), so you can achieve far better results with more lights closer to the illuminated area.

Also, it appears to my naive eyes that streetlights are mostly placed for the benefit of cars - they tend to be at intersections, off-ramps, etc. So if you imagine a world based on PRT it seems logical that you just need a lot less streetlights.

Not sure that the directionality of light is benefited by PRT, and similarly not sure that the ROI is there to add motion sensors for every light (or section of lights). I'd be happy to be proven wrong, though...

The similar, but unrelated benefit that your drawing reminded me of is the ugly-as-sin power lines running everywhere. You put high and low voltage wires (communication wires - cable, fiber optic, phone lines, etc.) into conduits up on top of the PRT line and whamo - the PRT line potentially beautifies the area (beauty is in the eye of the beholder, of course, so not everyone will agree with me there).

Dan said...

Dan The Blogger Responds-

I’m afraid I’m really not much of an expert on lighting, but I keep hearing buzz about how efficient LEDs have become. What I don’t know is how efficient they are compared to the traditional mercury vapor lamps, or other alternatives. Looking at my LED flashlights, I notice that they add candlepower by adding more LEDs. This leads me to the idea that brightness control can be added simply by having different LED clusters controlled individually. Also LEDs can switch on and off without burning out, so they are ideally suited to “smart” systems.

Whether or not such a system could be viable, or how “smart” it could be is a conversation that is a bit removed from PRT, but for the fact that the streetlights are liable to be in the way anyway, as are, as you pointed out, the telephone poles. This means the road to PRT adoption requires great solutions to these problems.

I don’t know what cities pay to keep the streetlights on, but if a PRT proposal also comes with the promise of a reduction in electricity costs as well as added safety, that sounds like a winner to me.

As for the other utilities, I agree. I must say, though, as I have looked around town at the poles I would do away with, this doesn’t look as easy as the lighting. First of all, wires come off of those poles directly to homes and businesses, often crossing the street. I hate to think of all of those wires coming off the PRT track, or of trying to sell a city and an electric company on burying them all, especially since they go directly on to private property. Secondly there is the easier problem of the transformers. They have to go somewhere.

So far I haven’t figured out what is in it for the utilities, other than greater protection from the weather, and no more poles to replace. We don’t want this to be become a great giveaway to them either, in the form of “cost – plus” contracts to do all of that rewiring. It sure would be nice if they were on board, though.

Bengt Gustafsson said...

Note that the wattage required for the same lamp technology is greatly reduced (50%?) just by having many small light sources. With a few strong light sources they must be dimensioned to give the minimum required brightness halfway between lamps, so below a lamp you get much more light than necessary.

One problem with a suspended PRT is that the vehicles will intermittently cover the light which would not only block light output but also create irritating blinkning for each passing vehicle.

In the Beamways system there are connecting bars every 6 m which would allow for this lamp spacing on dual direction lines. For single direction lines this is not available though, so this is a definite (although small) advantage for supported systems. Such lamps are shown on some recent Vectus images.

Dan said...

Dan The Blogger Responds:

It’s nice to hear from you, Bengt. I checked out your website, and will add the link when I get a bit of time. I was particularly interested in your proposed motors. The motors themselves spin, right? That is obviously the way to go, when the technology gets more widespread. If you have a source for “off-the –shelf” motors of this type, I would love to check out the specifications and prices.

As for the lights being blocked by the shadows of the PRT vehicles, there are clearly ways around this, especially if the lights are many highly directed beams, such as would be practical with LEDs. (light emitting diodes) I know my picture shows only 7 lights between posts but there could be many more, aimed differently, so that a smaller fraction of light is blocked. There could also be highly directed lights on the bottom of the vehicle itself, visible only when looking up at the shadow of the vehicle against the rail-mounted lights.

Bengt Gustafsson said...

There is at least one source of reasonable wheel motors for PRT:

For the streetlight/shadow problem, I think that "replacement" light under the cabin could actually be a good idea, the moving shadow effect on the ground could be reduced by a fair amount.