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Constant-Flow Major-Street Layout

It is possible to design a city's street system so that it is safe to have no traffic lights anywhere.
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(+6, -5)
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For everyone who wants to fishbone this idea (another that I happened to independently dream up a bunch of years ago), feel free to use the excuse that this can only work in cities that are built around the idea from the start (and will be VERY expensive! -- and will probably be boring to the inhabitants, too).

This idea CAN be used with a square grid, and is a little simpler to engineer, and would be more "normal" to current city dwellers. However, since I am talking about something that willy-nilly has to be built from scratch (same as tearing down and rebuilding entire city), I prefer to start with a layout that maximizes efficient auto transport from any Point A to any other Point B within the city. Please remember that people can become accustomed to just about anything that is not actually harmful, if they are immersed in it long enough.

So: Imagine a trangular street grid:


MAJOR streets are depicted, spaced perhaps one kilometer apart (a little more than half a mile). Within the triangular regions the land is used in the ordinary way, for businesses, residences, etcetera; minor streets inside those areas should also have a triangular layout, and have the usual maximum speed limit of 40kph/25mph; all those intersections would be controlled by Stop and/or Yield signs (not the same as traffic lights).

All streets (both major and minor) are one-way. Their direction of traffic flow alternates, of course. Minor streets are all single-lane (perhaps with room for parked cars on each side), but each major street consists of at least five lanes; the more optimistic future cities may prefer to make plans for six or more lanes for each one-way major street.

The usage-breakdown for each one-way major street is this: The outer two lanes are reserved for accelleration/decelleration of cars entering/leaving traffic in the low-speed triangular regions ("trangs", anyone?). These lanes, and the immediately adacent lanes, will follow the road plan around corners. For an intersection that allows a right turn, the two lanes will diverge to the right (NOT flow through). And for an intersection that allows a left turn, the two left lanes will diverge to the left. So that's four lanes accounted for, so far. All other lanes (one or more, that is), in exact center of traffic flow, will flow straight though each intersection, with the following caveat:

Since each intersection features 3 one-way streets going in 3 different directions, here is how we prevent accidents and avoid traffic lights: One street will take an overpass across the intersection; one street will take an underpass, and the third street will go straight through at ground level. The lanes of each street that are going around the corners will be banked, to allow good traffic speed.

Folks, this scheme definitely works on paper. It is the triangular layout, and accompanying mostly-diagonal traffic flow, that allows efficient traffic-routing. One detail that can be overlooked is the fact that while two lanes may curve away from the right, and two from the left, as an intersection is approached, two more lanes will join up on each side, as the intersection is left behind. This will be true for every intersection. However, because of the directions in which one-way traffic can enter/leave each intersection, two fundamental intersection designs are required -- one is a bit spaghetti-like. Yet remember that these intersections are a lot simpler than they would have to be to accommodate streets that carry two-way traffic -- and standardized designs means economy-of-scale with respect to prefabricating structural components. for so many major intersections in the city.

Of course, if some city preferred to use a square-grid one-way layout, the intersections would be simpler yet, and all would be of the same design. But traffic routing would be less efficient, partly because someone cruising along will only be able to turn toward one new direction at each intersection, and not have a choice of two directions.

Still, regardless of the chosen grid, the lack of traffic lights should lead to a great deal less congestion (and maybe even fewer accidents than occurs now!).

Vernon, Apr 16 2002

Swindon's "Magic Roundabout" http://www.swindonw.../life/lifemagi0.htm
Don't even go there. I mean that literally. [angel, Apr 17 2002, last modified Oct 21 2004]

Shrewsbury http://www.streetma...2200&arrow=Y&zoom=5
Click to go eastwards to the town which shall not speak its name... [sappho, Apr 17 2002, last modified Oct 04 2004]

Milton Keynes http://www.streetma...7500&arrow=N&zoom=5
check out the roundabouts on that! [sappho, Apr 17 2002, last modified Oct 04 2004]

Livingston http://www.streetma...500&Y=668500&zoom=3
Makes Life Not Worth Living(ston) [sappho, Apr 17 2002, last modified Oct 04 2004]


       and what is the facility for pedestrians, cyclists and public transport stopping points?
sappho, Apr 16 2002

       My city is built in a square grid from scratch, with four main avenues running right around the outside. It's almost impossible to get lost in it.   

       Boring? If I was forced to travel at 40kms/25mph it probably would be. I don't think my car can go that slow.
Helium, Apr 16 2002

       Milton Keynes?
sappho, Apr 16 2002

mcscotland, Apr 16 2002

       Great Falls, Montana, U.S. has no stop /yield signs and very few traffic lights. This is the same state that eliminated their speed limit a few years ago (but has since brought it back for night-time driving). Since everyone knows that no one has the right of way, everyone is more careful when approaching an intersection.
phoenix, Apr 16 2002

       Maybe I missed this, but if the intersections don't actually intersect, how do you turn? If you've got off-ramps/on-ramps at every intersection, then how much room is left for the stuff all these roads are supposed to lead to?
bookworm, Apr 16 2002

       "Try getting around a city that uses roundabouts instead."
That would be Telford, Shropshire.
sappho, Apr 16 2002

       Would lead to very intersting buildings, though.
[ sctld ], Apr 16 2002

       Maybe this would require establishing new cardinal directions to replace North, south... etc.   

       Try using North, Sest, Erst to keep people from saying Southwest, southeast...
spew, Apr 16 2002

       sappho, that is a good objection. With respect to public transportation such as buses, however they should not be a problem, if the bus stops were placed in the middle of each side of each trang (they would be stopping in the lane dedicated to acceleration/deceleration, which most traffic will prefer to avoid). Bus ROUTING, however, poses a completely different problem, since there are many streets, and none of the major ones are more major than any of the other major ones.   

       As for pedestrians and cyclists, well, certainly sidewalks can line the edges of each trang, but you are wondering about crossing from trang to trang. I think I would recommend pedestrian bridges located at the bus stops. Remember that within the trangs there will be minor streets, and some of them can certainly lead fairly straight from center of one side to centers of the other two sides. So pedestrian and bicycle traffic can short-cut through the central area of each trang, rather than taking the long way around the sides (unless the long way was desired, of course).   

       Helium, I did not mean to imply that just because the traffic on the minor streets within each trang would be limited to 25mph, that the traffic on the major streets would also have that speed limit. It should be safe for major-street traffic to do freeway speeds, except at the right-most and left-most lanes!   

       bookworm, the intersections in this design are generally smaller than you see everywhere today, because only one-way and not two-way traffic need be accommodated. Also, just because I described half-click spacing of the major one-way streets, that does not mean that it cannot be changed. A minor change, for example, might be to ensure that each trang is 500 meters (more than 540 yards) on edge. The roads merely separate the trangs by whatever width the city chooses, and plans for. Of course, each trang could be specified as 600 or 750 or more meters on edge, if desired. You will find that there is plenty of space within each trang to accommodate most anything. About the only thing that might have trouble fitting within a trang is an automobile assembly plant. (And yes, I know that pedestrians would probably have to walk around something like that, to get at the next ped-bridge.)   

       sctld, just because the landscape turns triangular, that does not mean all buildings must do the same. Besides, I did mention that a city could go with a standard square grid, if it wished.   

       spew, yes, for a triangular-street grid, some new names for the primary directions would indeed be needed. Note that while the main idea shows a depiction of what might be pure east-west streets, that is not a thing to declare as fixed. Pure north-south streets might be chosen instead -- or NONE of the streets might be aligned with any standard direction, deliberately, just to discourage standard four-direction thinking.
Vernon, Apr 17 2002

       Dammit Sappho, now look what you've done-people are asking questions about Telford. Well it's not there and it never has been, just ask anyone aound here, they'll back me up, although I live within twenty miles of T*lf*rd I never saw it and it doesn't exist. There some things you just have to accept on faith alone so just trust me on this. You never went there and you never even saw it. OK?
IvanIdea, Apr 17 2002

       Sorry, IvanIdea. Actually I was wrong anyway, I was thinking of Shrewsbury. See link, UnaBubba, and note the A5 skirting round the southern side of the town. Note also the roads through the town, there is a red one which does appear to have roundabouts all the way through it.

Vernon, I thought that's what you'd say for buses. Reasonable enough. However, I also expected that bridges would be your proposed solution to the pedestrian question, and I am now wondering what sort of scale your 'trangs' have, and whether you really expect my granny (who doesn't own a car) to walk six blocks (she won't call them these fancy new names) to get to the chemist for her arthritis prescription... and have to climb a bridge after each block? These would necessarily be at least a storey high, to allow clearance for larger vehicles on the major roads. Another pedestrian/cyclist option is tunnels. My granny will not feel safe in tunnels. Neither, for that matter, will I.
I applaud your avant garde sense of town planning, in using the vertical dimension to solve traffic issues, but I don't think it is applicable in such uniformity, or where there is any chance of people actually wanting to walk anywhere. I understand that people don't walk much in the USA, and that pedestrians would be very well served by the low speed limit inside your 'trangs', but wouldn't that artificially segregate or even ghetto-ise your city? Nice concept, neeever gonna work, you can keep it for Sim City, thanks all the same.
sappho, Apr 17 2002

       You can name Shrewsbury Sappho, just not you know what. I drive that road twice every day and can confirm that it is riddled with roundabouts and they are a pain in a car but a joy on a bike. But before I get reminded that this is not a chatroom I have a point. There is a very squiggly blue line running through the map you linked. This is a very big river. Vernon how would your system deal with such errant natural obstacles, you really couldn't have 5 lane bridges at very regular intervals but otherwise wouldn't horrible bottlenecks arise as they do now and which are a big problem with traffic management . Also you have to deal with steep hills, gorges etc ?
IvanIdea, Apr 17 2002

       sappho, a variant of the pedestrian bridge thing is to keep them ground level, and have all the cars dip under them. After all, the cars will be goin up and down at most intersections, anyway. Some people might move to such a city just for that "roller coaster" feeling!   

       IvanIdea, yes, topography can be very expensive to deal with. Technologically speaking, if we wanted to spend the money, a city like this could be built anywhere. We can make bridge/causeways over water, and even intersections, if we want to ignore the river that runs through a city. Dealing with water-borne shipping then becomes yet another expense, more so than a technical problem. And bridges for gorges, and so on. All it takes is lots and lots of bucks. Practically speaking, therefore, this city design is not for just anywhere. And I already mentioned the expense right at the start of the idea.   

       Now it happens that yet another variation of the overall idea is to put the roads underground, at two or three different levels (depending on square or triangle grid). Again, though, it is just a matter of extreme expense. In a way, if it wasnt' for the expense, it's kind of neat to think of ALL "infrastructure" as going underground, in neatly laid out networks. Spare no expense! Slidewalks, power, communications, water, sewage, mass transit, personal transit, factories, power plants, offices, shops, EVERYTHING but the residences go underground....and every residence has an elevator to all access to any of the networks.
Vernon, Apr 17 2002

       Sorry to be a pain, Vernon, but I can't let you get away with this. All roads underground? In this utopian traffic world you are creating, does no-one ever have an accident? As now, we sometimes airlift people out of RTA situations. We also use helicopters to aid radio stations' traffic updates, and the police. Surely you are not proposing CCTV throughout this tunnel network? More labour to monitor all those views. OK, so put the roads all on bridges, above ground, the city is entirely pedestrian/cycle friendly, yet the engineering costs of the roads to put them on these bridges (same problem for tunnels) have rocketed. And people's back gardens are a bit over-shadowed. I'm having trouble visualising how intersections between minor and major roads would work - all vehicles raised up into lane 1 in lifts? bending of space-time continuua?
As I said before, great concept, totally sci-fi, totally outside budget, and since almost no-one builds towns completely from scratch*, this is a solution without a problem.

*you might be able to sell the idea to the Israelis/Palestinians, though. (Whoever "wins") They'll probably need some extensive town generation soon enough.
sappho, Apr 17 2002

       One promising aspect of this idea is that soil scooped out to make underpasses would be available to make overpasses. Also the regularity of the pattern would encourage the development of reusable robots to do the construction. It wouldn't necessarily be prohibitively expensive.
0ominous, Apr 17 2002

       I return to the half-bakery with little fanfare, to quietly express my surprise that no one has pointed out the most glaring flaw in this plan, as I see it:   

       Without sparing words, Vernon proposes that these trangs span the length of 540 yards or so on each side, with some number of minor access roads into the trang, forming minor "sub-trangs" if you will. If the center lanes of these major streets are going to be travelling at freeway speeds (and folks, we would be lucky if they can hold them down to as low as ten MPH faster than that), and the outside lanes are occupied with the myriad commuters branching off into their uncoordinated separate directions, including, but not limited to, major direction changes (possibly speedy enough, provided the ramps are unobstructed by driveways, etc), minor road turn-offs (quite slow, given the possibility of a necessary 240-degree turn), driveway access into parking lots and such (dreadfully congesting) and the curb-side stops of all modes of transportation (parallel parking, passenger pick-up, bakery turck deliveries), with all of this, we have such a disparity of speeds between the center lanes and outside lanes that lane changing between them will be a greater hazard than the occasional stoplight-controlled intersection, especially given the necessary limit to the block size (the 540 yards as stated above). Drive 540 yards at freeway speed and decide how uncongested your lane would remain while, of the number of drivers on a block in a metropolitan area, even as low as say ten percent are all trying to slip into a lane that is slowed by the above stated activities.   

       In a word, NOT.   

       (BTW, have I missed anything good?)
globaltourniquet, Apr 17 2002

       As long as the routes make circuits I don't see the need for geometrical road layouts.   

       Can anyone quantify the savings due to fast non-stop traffic flow? Would the savings pay for the extra cost of building circuits of non-stop intersections?   

       globaltourniquet, the major fast roads would have to have no parking, side roads, or clutter. Bus stops, if any, would have to be in laybys. Crossing the fast lane would be a problem though. Could the idea be modified to put all the exits on the right or on the left? Turning the other way would involve some kind of loop.
0ominous, Apr 17 2002

       Hey UB old pal. Well, evil forces conspired to keep me from the fellowship. Wait a minute. Who you callin' "boy"?
globaltourniquet, Apr 17 2002

       sappho, I wasn't really trying to push (very hard) the idea of all-underground roadways. It was sort-of a daydream about achieving landscape beautification. You are right that accident-rescue would pose a problem, but your solution of all-elevated roads strikes me as an enormous eyesore. Hmmmm... it occurs to me that if someplace actually went to the expense of building all those tunnels, well, because tunnels tend to be round, it might be possible to put suspended-monorail tracks along the top arch of every tunnel, for use by emergency teams.   

       globaltourniquet, the obvious rebuttal to the problem you describe, about accidents during lane-changes, is individual-lane speed-recommendations (and more center lanes of max allowed speed). Consider that in many cities a reasonably important street may have a speed limit of 40mph, but you can turn off such a street into a residential street where the max speed is 25mph. Certainly you have to slow down to make the turn, but you can often make that turn at 25mph, so your change-of-speed is the 15mph difference. Next, consider that while auto makers like to brag about 0-60mph performance, it is not a leap to see that acceleration-wise, a 25-40mph is usually not a hugely time-consuming thing. So I suggest that the designated decelleration/acceleration lanes have a max speed of 40mph, while the next lanes in toward the center have a max speed of 55mph, and so on. Surely you have many times encountered 15mph differences in speed of cars in different lanes on existing highways, and you may even agree that relatively few accidents have resulted from that.   








       Next, I'll use the above lines two different ways. First, think of them as being the lines that designate six traffic lanes on a major road (ignore <> symbols; all traffic goes one way, let's assume towards the right). The uppermost and lowermost lanes are designated 'celeration lanes, 40mph. Your concern about side streets into the trangs is worthy, but not so terrible. because Oominous has the right of it:.   


       Let's pretend this line represents a 'celeration lane along one 500 meter side of a trang, with minor-street connections every 100 meters (comparable to size of residential block). Remember that the minor streets are one-way, also! So a car diving into one of the \/ connectors doesn't have to worry about cars coming out at that spot, and because two minor roads merge/intersect at the connection with the major street, there can be room to make that 120-degree corner, as well as the obviously-easy 60-degree corner. (The B represents the bus-stop zone, and it could be easiest if the bus drove around that mini-trang, where it could stop and not interfere with traffic on the major street.)   

       Next, both the 'celeration lanes and their immediate-neighbor lanes are also turn-lanes, on the major street: They WILL turn at a major-street intersection. (Thus one way to encourage a max speed limit of 55mph in those adjacent lanes is to design the banked curves to be unsafe at a faster speed. The laws of Physics can help weed stupidity out of the population, heh heh.) Then the two center lanes could theoretically/safely allow a max speed of 70mph.   

       The other way to look at the first set of lines is to think of them as each represting an entire one-way major street. As mentioned, they may be spaced 500 meters or so apart (not fixed, remember, so let's up that to half-a mile for the moment). Now compare an ordinary city with a square grid of two-way major streets, spaced between a kilometer and a mile apart. (Few cities manage perfect regularity, unless the ground is relatively flat and dry, so Phoenix and Tucson come close.) Anyway, in such an ordinary city, traffic going one particular direction is spaced perhaps a mile from another lane of traffic (on a different major street) going that same direction. In the traffic layout described here, the same spacing is true!
Vernon, Apr 18 2002

       Hmmm . . . here we go . . . damn street too narrow _/—\_ gotta get home 'fore night . . . whatcha goin' on 'bout? V?
neelandan, Apr 18 2002

       Hi, [global]. Sealy's gone.
angel, Apr 18 2002

       i take this as a utopia and believe that details have to be studied later... At this stage details could bring any idea to an halt...   

       One way idea reminded me the Brasilia City (Capital of Brasil) which is basically composed of circles (main roads) with diffrent radiuses aligned at a same center. I blended this, with your idea and what came out is the sunflower pattern... In a sunflower pattern you have many many circles (center of this circles are also looping). Besides its denser in the center and streches as you move farther from the center, which could be benefitical for future city development. More streched areas for the industrial lands, and denser areas for the shopping and city center functions.   

       But no triangles on this one, instead four sided islands, which can be cut into two triangles at will...Lets reserve this shortest paths for the pedestrian traffic only, especially in the denser center, so it would be possible to reach some point by walking. The cars have to speed up... and loop.   

       Its still half-baked (is there any baked city concept yet anyway?)... I'm with the angled pattern, which guarantees the future open spaces... and is less likely to be a claustroophobic city like NewYork in the future. It may make the round sectioned buildings more apeealing. Round section is tthe most cost effective one for the public buildigs, both to construct and to operate...   

       This could provide a nice generating pattern for architects for detail solving... and i believe dynamic, joyful open spaces can be generated... But more mind-challanging people will be needed to find out which circle to loop in to get to a desired adress... Well, adressing, another tiny detail :)
Aykam, May 15 2002

       And if we blend the sunflower pattern with your triangle idea, this time the honeycomb pattern would came out... Hmmm... 18 zillions of bees can't be wrong :)
Aykam, May 15 2002


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