Talk:Personal rapid transit

Gravities vs. m/s^2

I think gravities are more meaningful for an average person, and this is an encyclopedia. So, I plan to put the gravities as the primary unit, with m/s^2 in parenthesis.

misc

Reverted away from copyrighted text from www.lightrailnow.org/features/f_prt_2005-01.htm

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Braking

The braking gravity forces here seem crazy. Is there any documentation to prove we will survive braking from 115 km/h in 0.1 seconds? AndrewR66 2004-10-06

... also

However, these numbers seem very suspicious, considering that a car stopping from 70mph in half a second requires the passengers to have seat belts to keep them from flying through the windshield. And a stop from 70 mph in 27 feet seems almost impossible without some sort of permanent structural damage to the car, the guideway, or both.

Sorry, but this is basic physics and engineering. First, no-one would advocate these stops as standard operating procedure. These are emergency stops. Extremities will flail around, and there might be minor injuries. Automobiles perform emergency stops at 30Gs with steel "crumple zones," but there is another way. A PRT can brake by grabbing a rail or linear motor; cars can't because their tires slip. In car accidents it isn't the gross deceleration that harms, it's things that pierce or bludgeon the car and human body. Since the PRT never leaves the track, and cannot collide with anything (it's above grade), piercing and budgeoning is unlikely. As for the braking rail, the tensile yield strength of mild structural steel is more than 30,000 pounds per square inch (exotic cable steels go as high as 250,000 pounds), so a few square inches of cross-section can form the 30G braking rail(s) for a 1200 pound (heavy) PRT car. Solve for time and distance to get the "absurdly short" distances. 1G = 9.98 meters per second per second. The standard equation of deceleration is V=0.5*a*t^2 where V is the change in velocity, a is acceleration in meters per second per second, and t is time in seconds. The accelerations are standard for safety engineering. The thirty gravity deceleration was first validated by U.S. Air Force rocket sled experiments in the 1950s with Col. John Stapp. See info about John Stapp. It is now widely used for automobile designs. User:Ray Van De Walker

I'm sorry, but this is entirely incorrect. The speed of deceleration is the primary factor in injuries in any kind of accident, whether PRT or otherwise. The fact that a vehicle is able to decelerate quickly has no bearing on the fact that its passengers cannot. Even if their torsos are restrained by a seat belt, their head and limbs are not, and will attempt to continue to travel at the initial velocity. At the speeds you have given, the deceleration alone is quite sufficient to cause severe injury and even death (and of course unrestrained passengers will simply fly through the windshield, regardless of whether there is anything else to collide with). The studies you refer to are in reference to fully restrained decelerations, which gives no opportunity for the sort of neck-stretching injuries that ordinary decelerations produce. Unless PRT passengers are facing backwards and wrapped in a cocoon, which they are not, those studies have no bearing on this situation.

The reason that PRT guideways can sustain much higher traffic rate has absolutely nothing to do with stopping distance; in fact, their stopping distance is generally longer than an automobile's. Rather, it is their computer-controlled reaction time which is the critical factor. This is why the DMV recommends a 2-second separation between street vehicles (also known as the headway distance); not because a car traveling at 65 mph can stop in two seconds, but because that's the reaction time of the average driver. Once the driver reacts, they can apply the brakes and presumably match the deceleration rate of whatever is in front of them. Because PRT vehicles are computer-controlled, their reaction time is measured in milliseconds instead of seconds. This allows for much shorter headway distances, and much higher traffic flows.

This is a very serious problem with this article, and I will endeavor to fix it as soon as I can dig up the definitive references. User:Skybum

There have been substantial changes to the braking information, and they've been reviewed by helpful experts from ATRA, and have not changed for many months, so probably this topic is now authoritatively addressed. User:Ray Van De Walker 2005-10-4

Why is braking distance so important? When one drives a car, one certainly can not stop in the distance between cars. What am I missing? pstudier 22:18, 2005 Apr 6 (UTC)

I at least, am a more cautious driver than the people in your area. Some of us might say we're willing to take the risk, but some people who say they are willing to take the risk might change their minds after they have an accident. So, in most places, safety laws require public transit vehicles to keep a full stopping distance between themselves and anything they could hit. This lowers the number of vehicles that can fit on the road or guideway or whatever. In turn, this reduces the rate at which the road or guideway can be depreciated. This in turn increases the fares or public costs substantially, because the roads or guideways are the most expensive part of a transport system. User:Ray Van De Walker

WVU PRT separate article?

WVU PRT should be seperate article? wikiveterans please advise Codeczero 16:29 Feb 21, 2003 (UTC)

Hi, welcome! As it is, WVU PRT fits well in this article: it is on-topic, and only when an article gets very long we need to split it. - Patrick 20:26 Feb 21, 2003 (UTC)

good info in here but it reads like someones PRO PRT lobbying piece still.. Triptych 02:57, 9 Jan 2004 (UTC)

Not anymore. There are quite a lot of disadvantages listed, and I just put in the guideway choice issue and the dual mode versus single mode debate. Now, the problem is to get the article organized a bit more. Too many of the points mentioned (as advantages or disadvantages or as specs) apply only to one type of guideway but not to another or to a single mode system but not a dual mode system, and this is not made clear.

I wrote the original article, and I'm still one of the biggest contributors (I often fail to log in). I started off pretty ignorant, and very neutral on the topic. I have experience with biomedical software and safety engineering. So I read up on the topic. Unfortunately, most of the people who write books about this thing, and really understand it are enthusiasts (of course). Most of the people who debunk it are clearly doing the capitalization and overhead math wrong. Some of the older advocates say this is happening on purpose to persuade the politicians to buy the wrong transit stuff. User:Ray Van De Walker 2004-01-27 09:20Z

I am always amazed at the naivete of alas too many PRT enthusiasts (and here I am not refering to those who have edited this article, for they seem a level headed lot) and sympathisers . No, PRT systems are not singled out specifically for destruction, yes they will get destroyed mercilessly if they are not nimble. The transit market is all too often a "dog eat dog" world of rather fierce competition between competing kinds of systems, competing companies within the same systems and local financial interests striving for attention. PRT projects get caught in the crossfire most of the time, or brushed aside with a slight shove because of their fragility. Entrenched transit technologies in traditional transport establishments can react in a very brutal way to menacing innovations, and this has happened to much stronger and well prepared projects than what PRT systems are offering. One example is the air cushion aerotrain developped by Jean Bertin in France. It went as far as full scale prototypes and a long test track several kilometers long. The development of the TGV, the Train Grande Vitesse (ultra high speed train) by France's national railways, the SNCF was an effort meant to crush the aerotrain, which it considered as a dangerous competitor. Hundeds of millions of Euros were spent in R and D by the SNCF, dwarfing the aerotrain research budget. Even greater sums were spent on the new dedicated infrastructure for the TGV. The SNCF was successful. Companies which sell trams, buses or or commuter wagons cannot be expected to lie down and say . "OK you have the right stuff and we have the wrong stuff." They can be expected to try every trick in the book to wipe any PRT proposal off the map, as they wipe out other competitors in the traditional bus and tram domain. The only potential allies are car companies, which stand to gain as much by making myriads of PRT vehicles as they are making cars, if personal vehicles are allowed (in single mode as well as in dual modes personal vehicles are possible, though they are rarely discussed) but there is no reason for them to leave the status quo. One should note though that Ford research labs proposed a new PRT system called PRISM, in December 2003.

Some sort of PRT planned in Finland

I can remember reading an article about some sort of a trial of a PRT system being planned in Finland. If I can remember right, it would (at first) be a line from Helsinki-Vantaa airport to some points in Helsinki (or well, they called it a high speed "driverless taxi" moving on a predesigned route, as far as I can remember, but isnt that a PRT system then..). Would anyone have any more info on this, as I couldnt find anything from Google? It would be an interesting addition to the article.--HJV 20:35, 27 August 2005 (UTC)