Wednesday, December 24, 2008

12> Station Safety and Sinking Santa

First of all, I wish to thank alert readers timote and Dave Smith (TO?) for their valuable contributions. (Also Transportation Enthusiast, who I have since witnessed eloquently correcting a (less-than-enlightened) anti-PRT blog.
The question of collisions at the loading zone/station is a very real one. I had originally imagined “pods” as being very small, probably just 2 seaters, as the idea of building miles of track gauged for third and forth passengers, which statistically don’t exist seemed wasteful in terms of steel, and would make the track and supports thicker and therefore more visually intrusive. There is also the matter of safety, as heavy objects obviously carry more inertia, particularly at cruising speed. At the time, however, I hadn’t given much thought to light freight usages nor traffic density control. My current thinking is that the possibility of freight delivery could be lucrative. As I have written in a soon to be published post, delivery in gridlock is an expensive fact of life for many companies. These entities might have some influence towards PRT adoption. For them bigger is better. Also claustrophobia is an issue with some people, and a little extra space and larger windows would help. Personally, a port-holed coffin sized pod is fine for me, but I’m not your average person. Anyway, as for collisions at stations, I had always thought of a total load (pod, motor, and payload) of less than 750 lbs, traveling at walking speed. This is probably one half of the actual weight I’m comptemplating now, although I am still for excluding four “large” adults. So the question is, “how slow would a (beeping) object of, say 1500 lbs. have to move to not require an expensive station infrastructure?”
My guess mix is 10 ft. per 20 seconds, with striped pavement, possibly cordoned off with chains, a low to medium volume beep-alert, and tilt/bumper sensors on the pod, so that it will cut power if it hits an obstruction that can’t be pushed with just a few pounds.
Part of the reason that open-source PRT is superior to waiting for a company to sell us the solution is that the safety decisions don’t require the overkill that we would want from a corporation whose decisions are primarily profit-based. Certain risks are assumed to exist. Sidewalks are more dangerous because they’re close to streets. So what? I have yet to see the lawsuit requiring cities to move them or demanding damages. Trains and subways and buses and, yes, PRT can’t stop on a dime. But safety parameters designed by a non-profit open-standards organization are not particularly tasty bait for litigation, and PRT could get very slow as it descends.
Finally, Happy holidays! Here is a depiction of me Photoshopped into a Santa Claus photo that went on to consider the ramifications of global warming on the Santa’s base of operations. Imagine Santa’s waterfront property. And the cats? Hey, Everyone loves cute kittens…


timote said...

Ok, so let me reiterate what I think your concept is:

There are no stations. There are only designated stopping places, with little to no infrastructure involved. When the pod comes down from the track, it slows to a snails pace and is the equivalent of a parking car or a electric wheelchair or the like - if you get hit by it, you weren't paying attention and/or were where you weren't supposed to be.

I'm intrigued by the concept. It flies in the face of the "standard" PRT concept of costly stations (very often at elevation, so elevator rqd), but it brings the concept that PRT could come to my suburban door (or at least to my block, a lot closer than the 1/2 mile separation usually discussed).

I think both could be possible - you could still have defined stations in higher density areas - intermodal transit stations, the grocery store, Wal-mart strip mall, the mall, downtown skyscrapers, etc.

So here's my next question - how do you call one of the things? For a pretty high techie like myself, whipping out an iPhone with GPS and choosing a no-infrastructure "station" near myself is pretty straightforward, but I'm not sure that's feasible for my Grandma.

timote said...

Oops - I already asked the question in a previous comment. Well I guess I'm asking it again :-)

timote said...

Ya, I think that could work. For a residential application, I'd red-paint off about two car length parking spots and have the pod "park" on the street, I think (plus markings that this is a PRT drop-off, of course). So long as it is on the street, a pedestrian accident is much more acceptable - if I step off the sidewalk in front of a podcar crawling into a parking spot, I'm at fault.

BTW I think you're right in re-thinking the two-seater concept. Two seater would work for commuter (and maybe could be the standard configuration), but I think you need to have four seater options for families and similarly larger (unmanned) cargo pods.

The cargo pods would have to have designated drop-off/pick-ups. That is, you cannot have unmanned cargo pods stopping on my block - they only stop at a designated cargo stop (presumably manned for receiving) where they can hang out for a while to get unloaded.

This gets into a whole question of authorization - as an individual commuter I cannot request a drop off at the Walmart receiving dock (especially if the dock is actually in the building for security/ease of unloading). But this is a software issue and shouldn't affect the mechanical design too much.

Dan said...

Thanks for your interest, timote. I’m pretty new to blogging, so responding to a comment with a comment, thereby creating a forum, of sorts, is highly experimental on my end. I must say I like the concept. Someday I’ll have a web site designed for interactivity, but, ‘till then…
I basically agree with all that you have said. It’s too early in the design stage to preclude stations. My concern is for anything that builds in cost, so I have endeavored to design a system that does not require only expensive stations to be viable. We are talking building blocks. New ones can always be added if we get the basics right.
The size of the vehicles is, of course, a trade-off. Adding capacity means designing track spans for back-to-back, fully loaded vehicles of that capacity. (Or dynamic, weight-based spacing) Since track must span highways, it’s an exercise in bridge design, over and over. Every gram of added payload capacity might add thousands of kilograms of steel system-wide. I have not talked to any structural engineers about it, so my fingers are crossed. This will be discussed further in an upcoming post.
As for calling for a vehicle, I have, so far, assumed a card reader/touch screen combo. I guess the card would be rechargeable, or a credit/debit card could be charged. I would imagine commercial accounts could be set up, including freight accounts. I will eventually post about it, after I’ve given it some thought. I am worried about security, vandalism, terrorism, maintenance, power failures, local control on private property, etc.

timote said...

Re: card access. To me, it is vital to have real accounts from the perspective of vandalism. Public transit gets trashed, so I think you need to have a system for this. Call for a pod and it has vomit in it? Hit a button to reject it with an explanation, the pod goes straight to the maintanence yard and videotapes are checked with the result that the last guy gets a hefty cleaning charge. This isn't possible with cash anonymous rides. Security advocates would be up in arms, but it's a reasonable trade-off to me for a good experience.

I understand your reluctance to make the pods too heavy, but let's say you have a family of three. Always having to take two pods seems very limiting, and outright impossible for a single parent. A pod of four (or at least three) seems like a good compromise to me...

timote said...

Not security advocates, privacy advocates I meant.

A Transportation Enthusiast said...

I am a big fan of ultra-lightweight street-level stations like you envision. It's what I like best about ULTra PRT, but ULTra has a relatively long descent distance (10% grade climbing) which would eliminate street level stations in most places.

Mister PRT has a station that's a little more complex than you envision, but not much. It's basically your descent but with parallel loading berths branching off and walls around the whole thing. I'm betting you could add a wall to your design - think a bus stop shelter, only maybe a little bigger, to block out the area where the pod intersects the pedestrian area (10ft).

I'd be a little concerned about a completely open station like you envision. Maybe in the long term, if the pods have sophisticated obstacle detection, this will be doable, but in the short term a small walled-off area would be more palatable from a safety perspective. "Small" is the operative word here - with steep descent angles and a single inline berth, the amount of barrier would be very minimal (as I said, maybe a little bigger than a bus stop shelter).

To address the concern of calling the pod, I envision there being an pod in every station waiting; if someone takes that pod, another comes to replace it. If this is not the design, then a simple call button would be sufficient.

Miko said...

Here's a concept for simple stations. How about the pod descends straight down from the rails into a bus-stop size cubby. This could be done several ways, Probably the easiest would be for the pod to have a tether on which it could descend, and the station would have a guide pole that the pod attaches to to keep from swinging. With this concept, small stations could be set up with fairly small cost, and no elevators or stairs.

The major downside as I see it is that it adds complexity to the pod itself. However, I think an emergency descent system is necessary anyway, so setting it up so that it can ascend back up may not be as much of an addition as might be thought.

So basically we're trading complexity: simpler stations for more complex pods. It could be a worthwhile tradeoff.