I spotted this interchange idea on Jalopnik http://jalopnik.com/5497618/vortex-junction-the-next+gen-roundabout
Quote from: Stephane Dumas on March 22, 2010, 01:32:48 PM
I spotted this interchange idea on Jalopnik http://jalopnik.com/5497618/vortex-junction-the-next+gen-roundabout
It seems like a different person has posted about this on all the different fora I read. :hmmm:
rats, they patented the dang thing!
I came up with that when I was 6 and saw my first rotary/roundabout/traffic-circle/whatever they call it in your jurisdiction, in Massachusetts it was the Cape Cod Rotary and it was awful and I thought "why doesn't traffic enter from the *inside* and leave at the *outside* and therefore there'd be a lot less weaving".
for all I know, my dad still has the video in which I ask the question ... though likely he may have muted the audio track, as it was peppered with him also noting the trouble the M. F. Cape Cod Rotary caused!
That idea is imaginative, but completely useless. Nobody would want to build such a big interchange.
Less weaving, possibly, but MUCH LARGER right-of-way requirements. Might as well build a regular interchange.
Quote from: froggie on March 22, 2010, 02:05:56 PM
Less weaving, possibly, but MUCH LARGER right-of-way requirements. Might as well build a regular interchange.
could a regular interchange of that size handle six in/out paths (i.e. three roads intersecting, as in that diagram), or just the usual four? More generally, how does that configuration scale as we add more paths, compared to a regular interchange?
This "vortex" junction doesn't seem to cut the mustard to me.
The circulation would appear to work well for the one direction of travel indicated. But if a motorist were to enter at 4 and exit at 3, they'd be looking at cutting across 5 lanes of traffic or doing more than a full loop to get there.
They also mention putting something like a sports stadium in the middle, yet show no concept of how that might be accomplished. And if the middle of this thing could accommodate a sports arena (with required parking), it's probably looking at a half mile to mile radius from the center to the circulating roadway. Right of way alone would probably make this prohibitively expensive to build.
I'd guess a stack interchange, even with six entry/exit points, could be built on a smaller footprint. Whether a stack could be designed and built to be less expensive than the 'less complex but much larger' vortex would be another issue.
I also think it's a stupid idea. The number of bridges required will also add to the cost. It's also flawed in that if there are several freeways meeting at this point it means using the roundabout thingy to go straight through unless even more bridges are added to accommodate through traffic.
Why the loops? The exiting roadways could just as easily make a 90 degree right after a slight left. It'd be smoother and allow higher speeds without costing any extra.
Still, there is some very harsh weaving here. The concept, as presented, is flawed.
Although, I see plenty of potential to play with this and modify it. That flaw may be able to be worked around.
I am not real keen on the vortex interchange for the operational reasons Roadfro cites. However, if there are more than two intersecting roads and it is possible to build complementary infrastructure to prevent sterilization of land within the interchange area, it can be much more economic than a fully semidirectional design with direct connectors.
Here is the mathematics: for n intersecting freeways, you have 2n senses (directions of movement) total. Each sense has to have a direct connector with all the other senses except (1) itself and (2) the opposite sense. So the total number of direct connectors that has to be provided is 2n(2n - 2). For a simple four-level stack interchange n = 2 and the number of direct connectors is 8 (this counts the link ramps handling right-turning movements as direct connectors). For an intersection of three freeways n = 3 and the number of direct connectors is 24!
Quote from: agentsteel53 on March 22, 2010, 02:45:06 PM
could a regular interchange of that size handle six in/out paths (i.e. three roads intersecting, as in that diagram), or just the usual four? More generally, how does that configuration scale as we add more paths, compared to a regular interchange?
Especially if the 3 through routes (6 paths) don't need to meet at a single point, but can form sides of a triangle of roughly the same size. Use some c/d lanes and the weaving wouldn't be too disruptive of through traffic. You'd probably still have room for the stadium...
In a regular interchange, through traffic doesn't need to change lanes, but in the spiral model, wouldn't you have to move over two lanes to exit the opposite side? Not sure that's any more efficient than a regular interchange. But then, I don't know any examples of this kind of 6-path interchange, so there's nothing to compare it to.
Quote from: Duke87 on March 22, 2010, 06:20:11 PMWhy the loops? The exiting roadways could just as easily make a 90 degree right after a slight left. It'd be smoother and allow higher speeds without costing any extra.
That approach results in flyovers which cross the circulating roadway at an oblique angle and thus have greater skew and deck square footage, unless you go under and use culverted undercrossings. (We don't use them much but they are very common in Spain, as are pergolas.)
Quote from: agentsteel53 on March 22, 2010, 02:45:06 PM
Quote from: froggie on March 22, 2010, 02:05:56 PM
Less weaving, possibly, but MUCH LARGER right-of-way requirements. Might as well build a regular interchange.
could a regular interchange of that size handle six in/out paths (i.e. three roads intersecting, as in that diagram), or just the usual four? More generally, how does that configuration scale as we add more paths, compared to a regular interchange?
I've modeled "regular" interchanges up to 8 paths. With six paths there are three ways to go - a double stack modified to stay within 4 levels, a modified cloverleaf with enough loops and fingers to serve everyone, or a hybrid stack/double clo that's my favorite. With eight paths, you pretty much end up with the double stack modified plus a hybrid cloverleaf laid on top of it. The six path interchange would pretty much fit in a right of way this large - you lose the room in the middle but gain more maneuverability. For less trafficked roads, you could just run a couple of the through roads on a second level and take away the through traffic from the conventional roundabout below.
Quote from: J N Winkler on March 22, 2010, 06:40:14 PM
For an intersection of three freeways n = 3 and the number of direct connectors is 24!
And this is why for something that large you start having combined ramps (think volleyball interchange with ramp weaves). Look at Garden State Parkway / US 9 / I-287 / NJ 440 / CR 514 for an example of a multi-path interchange that uses combined ramps (even combined with freeway mainlines) to accomplish the necessary moves.
After playing with it, this is what I've come up with (pardon the quick crude drawing):
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fimg638.imageshack.us%2Fimg638%2F1908%2Fvorteximproved.png&hash=9882f9ec34018995e6272818cc9681fb35231b70)
Only four spokes shown here for the sake of simplicity, but the same concept applies with more (would demand a larger radius, though).
Movement to the next consecutive spoke involves separate ramps that don't even enter the rotary proper. Entering the rotary itself and then following your lane will take you directly off three spokes ahead. Going only two spokes involves shifting left. Going four spokes (a U-turn in this case), involves shifting right. Going five would involve three lane shifts right, but not in the hugest of hurries.
Thoughts?
Left exits make the MUTCD cry...
Maybe you could add a right exit opposite the loops? It's too complex IMO.
From the looks of the modified interchange Duke87 created, going through the interchange without existing would require traffic to weave over to the left in order to stay on the same road. That thing would be a weaving nightmare.
The original interchange just seems like a waste of space to me.
Quote from: codyg1985 on March 23, 2010, 12:30:56 PMFrom the looks of the modified interchange Duke87 created, going through the interchange without existing would require traffic to weave over to the left in order to stay on the same road. That thing would be a weaving nightmare.
Yes, that is a problem. It could be solved by running the intersecting freeways through the interchange core, and I am pretty sure this could be done while keeping the number of levels crossing at any point down to two.
QuoteThe original interchange just seems like a waste of space to me.
It does have the potential to sterilize land, but I think this could be mitigated by building accesses to allow parcels within the interchange to be developed. The more serious problem, as I see it, is that it requires a TOTSO for all traffic passing through the interchange, even if it is continuing in the same direction. This could be eliminated as I suggested above (by running the freeways through the interchange core) but the tradeoff is that a crossing structure has to be provided in the middle with one level for every intersecting freeway.
Because of the TOTSO requirement, the interchange design as proposed really works well only when the majority of the traffic is stopping in the middle of the interchange (e.g., at the sports stadium). If bridges have to be provided to avoid inconveniencing through traffic, the design problem becomes different and there are probably other solutions which are more efficient in terms of construction cost, use of land, etc.
I'm fairly convinced that any roundabout-esque interchange design with left exits/entrances just isn't going to work, without some mitigating factor that will start to make the design either too complex or too expensive.
Quote from: Scott5114 on March 23, 2010, 07:57:11 AM
Left exits make the MUTCD cry...
Actually, left exits make the AASHTO Green Book cry...
The MUTCD doesn't include much text about the physical design of interchanges, but only how to sign and stripe them. The "Green Book" (formally,
A Policy on Geometric Design of Highways and Streets) is the design standard many agencies use, or at least what they base their own design standards off of.
I was referring to all the new stuff with regards to left exits that was added in the 2009 MUTCD. Left exits now have to have an exit tab that is twice as big and with the word "LEFT" in black on yellow above "EXIT". For non-numbered exits, a yellow "LEFT" tab is required.
While I agree with the consensus that this is a bad idea for a freeway interchange, I think the original intent was to replace a regular roundabout at a location where low-speed surface streets intersect.
Of course, his basis for this was that the inside lanes for a roundabout are underutilized. If people use a roundabout properly, all lanes are used, even the inside ones, since the inside lane has the right of way to exit the roundabout at any given street.
Speaking of complex interchanges, does anyone see the usefulness of this monstrosity (http://i15core.utah.gov/InteractiveMap/) (click on exit 265 - Provo Center Street and then "design on" and zoom in)? Why in the world would they build that?? A simple diamond or SPUI interchange would suffice here, would it not? (As a side note that same project is building two diverging diamonds)
I think the Provo Center Street proposal is a wonderful design. It means all movements are freeflow with no traffic lights or stop signs. The only downside is southbound I-15 to westbound Center Street means doing an almost complete lap of the roundabout.
Quote from: realjd on March 23, 2010, 04:47:57 PM
While I agree with the consensus that this is a bad idea for a freeway interchange, I think the original intent was to replace a regular roundabout at a location where low-speed surface streets intersect.
If that's the case, it's even worse. If a regular surface streets intersect at something like this, it makes it even more prohibitively expensive to implement. I could *maybe* see it if some kind of large regional park would be put in the middle. But the whole interchange would still take up a large chunk of real estate in any kind of populated area.
Quote from: realjd on March 23, 2010, 04:47:57 PM
Of course, his basis for this was that the inside lanes for a roundabout are underutilized. If people use a roundabout properly, all lanes are used, even the inside ones, since the inside lane has the right of way to exit the roundabout at any given street.
The inner lane of a roundabout does not always have the right of way to exit at any exit of a roundabout. Generally the only time a driver in the inner lane should have a guaranteed right of way to exit is at the last exit before reaching the leg they started at.
It all depends on the design, though. A properly designed roundabout will have effective utilization of the inner lanes(s) based on the signs and markings that dictate the lane assignments. Of course, this assumes the roundabout has adequate advance signage, proper lane markings, and carries drivers intelligent enough to interpret these...which is not always the case.
The 2009 MUTCD shows typical lane markings at a variety of roundabout applications, far more guidance than the two or three figures of the previous manual. While not a design guide, the figures do give one a good idea of the way modern roundabouts should be designed.
Quote from: roadfro on March 23, 2010, 07:02:02 PM
The inner lane of a roundabout does not always have the right of way to exit at any exit of a roundabout. Generally the only time a driver in the inner lane should have a guaranteed right of way to exit is at the last exit before reaching the leg they started at.
All 2-lane roundabouts I've seen have been configured like this:
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fwww.scgov.net%2FPublicWorks%2FRoundabouts%2Fimages%2Fdouble_roundabout.gif&hash=59c541d6aec78baa89e9773bc577b29446f24ea4)
I thought it was standard that the left lane was for straight and left turns, while the right lane was for straight and right turns. The rule is always yield to traffic on the left, correct? That would include cars in the inside lane. The lane markings always match this as well. Not that people know to follow the rules. I frequently see people follow the right lane all the way around to make a left turn.
Is this not as standard as I thought?
That's not always the case. there are two 2-lane roundabouts/traffic circles here where the inside lane only has the right away at the stubs with the most traffic flow.
Also, think about a roundabout where a 4-lane road intersects a 2-lane road.
Also, the roundabout at NE 39th and Glisan in Portland is a full two lanes in each direction. In that case, the right lanes only turn right, while the left lanes have full movement.
I would think traffic in the left-hand lane that is exiting would be mercilessly rammed by traffic in the right-hand lane.
Quote from: realjd on March 23, 2010, 10:38:39 PM
The rule is always yield to traffic on the left, correct? That would include cars in the inside lane.
Actually, the rule is yield to traffic on the right. So, that would be correct for countries that drive on the left side of the road, but not for countries that drive on the right.
This "right hand rule" problem is why roundabouts work better in left side driving countries. Why do you think they're so popular in the UK?
Quote from: Duke87 on March 24, 2010, 01:10:31 PM
Actually, the rule is yield to traffic on the right. So, that would be correct for countries that drive on the left side of the road, but not for countries that drive on the right.
This "right hand rule" problem is why roundabouts work better in left side driving countries. Why do you think they're so popular in the UK?
The rule in left-drive countries is yield-to-the-right in roundabouts, but it's definitely yield-to-the-left in American ones. Otherwise traffic circulating would have to yield to traffic trying to enter! It's backwards from how it is at 4-way stops and other non-roundabout situations.
Here's the MUTCD standard for 2-lane roundabouts. The left lane has the choice to continue or to exit, the right lane must exit:
http://mutcd.fhwa.dot.gov/htm/2009/part3/fig3c_06_longdesc.htm
Every multi-lane roundabout I've seen has been set up this way, with the lane markings clearly forcing the right lane to either exit, or yield to traffic in the left lane trying to exit.
EDIT: Here's the MUTCD link for the standards for all the other roundabout configurations:
http://mutcd.fhwa.dot.gov/htm/2009/part3/part3c.htm
It looks like as long as you follow the lane lines, you're good to go, but some of those are crazy complicated!
Quote from: realjd on March 23, 2010, 10:38:39 PM
I thought it was standard that the left lane was for straight and left turns, while the right lane was for straight and right turns. (...) The lane markings always match this as well. Not that people know to follow the rules. I frequently see people follow the right lane all the way around to make a left turn.
Is this not as standard as I thought?
The lane assignment you mention is correct, provided that it's a two-lane roundabout with two lanes entering and exiting on all approaches. When there's differing numbers of lanes on the approaches, the markings inside the circulating roadway may not be standard in order to give drivers better positioning for internal circulation and exit. So it all depends on the design. This is why adequate marking and signing are crucial when you start installing multi-lane and other complex roundabouts. Where designed properly and used correctly, a driver should never need to change lanes within the circulating roadway to get to their desired exit.
This lack of smooth channelization appears to be another flaw in the vortex junction. Unless you're exiting the junction at the exit immediately before the leg you entered on, there is no channelization to destinations. The vortex will require significant amounts of merging to be effective...depending on the size and distance between the entrances and exits, this could result in a lot of dangerous weaving activity.
Quote from: realjd on March 23, 2010, 10:38:39 PM
The rule is always yield to traffic on the left, correct? That would include cars in the inside lane.
Quote from: Duke87 on March 24, 2010, 01:10:31 PM
This "right hand rule" problem is why roundabouts work better in left side driving countries. Why do you think they're so popular in the UK?
A better way to remember this, is that entering traffic must always yield to traffic in the circulating roadway. This avoids confusing "traffic on the left" between entering/circulating vehicles and vehicles in different lane positions. That rule of roundabouts is universal, no matter which side of the road the country drives on.
Roundabouts have been around the UK and Europe far longer than in the US. The first "modern" roundabouts in the US were installed in Las Vegas, NV around 1990, and they've been steadily gaining in popularity especially in the last 10 years as national guidelines and standards have emerged to deal with design issues.
^^^
Excellent info. Thanks!
Both Military Circle (http://maps.google.com/?ie=UTF8&ll=43.087515,-76.113566&spn=0.002903,0.006925&t=h&z=18) and Carrier Circle (http://maps.google.com/?ie=UTF8&ll=43.087782,-76.090348&spn=0.002903,0.006925&t=h&z=18) in Syracuse are two-lane (with some additional direct lanes). Here are two solutions for the multiple-lane issue:
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fmjr1990.webng.com%2FAARoads%2FR4-3.png&hash=f0c09c880ef517e11b6896c855af17b95012c3c1) (https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fmjr1990.webng.com%2FAARoads%2FR4-16.png&hash=d6e9e63a33841f8915760a44ad8b70dc1c1dbe42)
The circle at NY 38/NY 437 (http://maps.google.com/?ie=UTF8&ll=42.904677,-76.544406&spn=0.001456,0.003463&t=h&z=19) used to have two lanes but now has one. The left lane on NY 38 south approaching the circle has been marked to end just before the circle.
It's good to see that the MUTCD already incorporates markings for turbo roundabouts, the ones with a sort of pinwheel arrangement that throw traffic out of the circle rather than letting it get trapped in the inside lane. It eliminates the chance of a vehicle exiting the circle from the inside lane being t-boned by someone going around the circle in the outside lane. It basically moves that conflict point to the entering traffic, which already has to yield. It's a good way to get higher capacity multi-lane roundabouts without them becoming a total free-for-all. I believe they were developed in the Netherlands, but have any been built here in the US?
Here's an illustration, though in this case it doesn't allow for a u-turn movement. It's an interesting geometry, though I don't know if it can be adapted to a 5-way or greater intersection.
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fhomepage.mac.com%2Fjjakucyk%2Fturboroundabout.jpg&hash=c05a62c8129f212f3258fb30fc72dab609eb53c8)
Quote from: Michael on March 25, 2010, 03:19:47 PM
Both Military Circle (http://maps.google.com/?ie=UTF8&ll=43.087515,-76.113566&spn=0.002903,0.006925&t=h&z=18) and Carrier Circle (http://maps.google.com/?ie=UTF8&ll=43.087782,-76.090348&spn=0.002903,0.006925&t=h&z=18) in Syracuse are two-lane (with some additional direct lanes). Here are two solutions for the multiple-lane issue:
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fmjr1990.webng.com%2FAARoads%2FR4-3.png&hash=f0c09c880ef517e11b6896c855af17b95012c3c1) (https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fmjr1990.webng.com%2FAARoads%2FR4-16.png&hash=d6e9e63a33841f8915760a44ad8b70dc1c1dbe42)
The circle at NY 38/NY 437 (http://maps.google.com/?ie=UTF8&ll=42.904677,-76.544406&spn=0.001456,0.003463&t=h&z=19) used to have two lanes but now has one. The left lane on NY 38 south approaching the circle has been marked to end just before the circle.
Michael, your Military Circle and Carrier Circle examples above appear to be more like traffic circles (sometimes called "rotaries") than roundabouts. The interesting thing with these examples is that there's very little merge space between entrances and exits. The inner lane would appear to not really be used at all, except to pass when the right lane is considerably slowed down due to merging. These could probably be converted to higher-speed roundabouts without too much effort. However, the signs you suggest would not really be of use in these cases, though--in a situation like these, cars in the circulatory roadway should theoretically be traveling about the same speed.
the turbo still looks like it has some nasty two-lane weaving. Say I wish to exit at 3 o'clock, and I am currently at 6 o'clock going around...
regardless of whether or not I am in the inner lane or the outer lane of the two lanes, I will have to yield to traffic coming in at 6 o'clock in that inner lane, and then immediately to the middle lane of that incoming traffic as well. Either I merge one lane at a time (stopping in the inner lane, blocking incoming traffic, until the middle lane clears as well) or I merge two lanes at a time, which is potential suicide.
and meanwhile, traffic coming in will be merging inwards from the middle lane to the inner lane, if they intend to make a three-quarter turn and exit at 9 o'clock. Ouch - double-lane weave!
that said, the major problem I have with roundabouts is this:
assume two cars (me and another vehicle) are approaching the roundabout from opposite directions. I am intending to go straight. The other car may be wanting to turn right, go straight, or turn left.
if he is to turn right or go straight, we will not intersect, and I do not have to slow down. But if he is to turn left, he has right of way, and I have to slow down. there is a point where he has already entered the intersection, and I have not, where I need to make this decision and possibly needlessly slow down just because he may be crossing my path.
In fact, I may needlessly come to a complete stop to let him through, which entirely defeats the purpose of the roundabout, which is to prevent stick-shift drivers (see: 90% of Europe) from having to start from a complete stop.
so either I slow way down to allow myself to see all the possibilities in front of me (thereby inconveniencing myself and traffic behind me), or I barge through and get an unfortunate surprise.
at least at standard traffic lights, traffic making a left turn in front of straight-moving traffic has to yield.
Quote from: agentsteel53 on March 25, 2010, 08:41:31 PM
regardless of whether or not I am in the inner lane or the outer lane of the two lanes, I will have to yield to traffic coming in...
No, because traffic entering the circle has to yield to all traffic already in the circle. You pick the lane you enter based on where you want to exit, and you don't change lanes at all once you're in the circle. So if you're making a left turn, you get in the left lane, if you're going straight, you get in the center lane, and if you're turning right, you get in the right lane. You only wait when first entering the circle, once there's a gap in traffic (there's only two lanes you have to worry about) and you're in the circle, you have a clear path to wherever you're going.
Quote from: agentsteel53 on March 25, 2010, 08:45:44 PM
that said, the major problem I have with roundabouts is this...
You're right that roundabouts perform poorly when there's heavy left turning traffic. People are supposed to use their turn signals to indicate when they're leaving the circle, and that would help with your situation. Still, you're focusing on that one aspect without considering all the others where roundabouts have an advantage. While you might have to slow down or come to a complete stop, whether necessary or not, it's only for that one car. Once there's a gap, you can take it, but you can't do that at a signalized intersection. Also, and this is somewhat subjective, but I've noticed that you can usually tell if a car is staying in the circle or exiting, even if they don't signal. You can kind of tell by how they're circulating. If they're going around, they tend to hug the island, but if they're going to exit, they start to peel away. Either way, if you have a clear path with no cars in front of you, and this opposing driver causes you to have to stop completely, then you're probably approaching too fast as it is.
Quote from: jjakucyk on March 25, 2010, 08:59:37 PM
People are supposed to use their turn signals to indicate when they're leaving the circle, and that would help with your situation.
which turn signal would they use when they are still coming towards me and have not made the turn, at which point it is obvious that they will cross in front of me? Left turn signal to indicate that their overall course is a left turn? Right turn signal to denote that they will exit at the next branch (which would be the branch directly opposite me)? Or, no turn signal, which could mean any number of things.
QuoteI've noticed that you can usually tell if a car is staying in the circle or exiting, even if they don't signal.
I've found that relying on drivers to behave logically is asking for trouble. Especially at roundabouts/rotaries/traffic circles. I barely know the difference, and likely could not recite all the right-of-way laws associated with each. The average driver doesn't even know that there's a difference - it's all a "big scary circle thing" - hold your breath and hope you make it out the other side.
Quote from: jjakucyk on March 25, 2010, 08:46:36 PM
No, because traffic entering the circle has to yield to all traffic already in the circle.
wow, I got that completely backwards!
Quoteonce there's a gap in traffic (there's only two lanes you have to worry about) and you're in the circle, you have a clear path to wherever you're going.
waiting for a gap in traffic when there's only
one lane to worry about is plenty bad - having to execute a spontaneous double-merge sounds frightening. (It once took me 45 minutes to merge three lanes over on I-95 in Fort Lauderdale. Merging two lanes at a time seemed just a tiny bit less likely than being abducted by aliens.)
Quote from: agentsteel53 on March 25, 2010, 08:41:31 PM
the turbo still looks like it has some nasty two-lane weaving. Say I wish to exit at 3 o'clock, and I am currently at 6 o'clock going around...
regardless of whether or not I am in the inner lane or the outer lane of the two lanes, I will have to yield to traffic coming in at 6 o'clock in that inner lane, and then immediately to the middle lane of that incoming traffic as well. Either I merge one lane at a time (stopping in the inner lane, blocking incoming traffic, until the middle lane clears as well) or I merge two lanes at a time, which is potential suicide.
and meanwhile, traffic coming in will be merging inwards from the middle lane to the inner lane, if they intend to make a three-quarter turn and exit at 9 o'clock. Ouch - double-lane weave!
From what I see, the turbo roundabout depicted is adequately designed to not require lane changes/weaving within the roundabout, provided one is properly positioned prior to entering. It just doesn't allow for U-turns, and forces the right lane to turn right only (which would be better implemented if a bypass lane were installed).
What you say about yielding isn't correct though. Entering traffic always yields to the circulating traffic in a roundabout. It does not matter if the geometry of the roundabout guides you to a different lane while circulating.
Traffic coming in *should* already be positioned into the proper lane for their particular movement prior to entering the roundabout.
Quote from: agentsteel53 on March 25, 2010, 08:45:44 PM
that said, the major problem I have with roundabouts is this [...]
assume two cars (me and another vehicle) are approaching the roundabout from opposite directions. I am intending to go straight. The other car may be wanting to turn right, go straight, or turn left.
if he is to turn right or go straight, we will not intersect, and I do not have to slow down. But if he is to turn left, he has right of way, and I have to slow down. there is a point where he has already entered the intersection, and I have not, where I need to make this decision and possibly needlessly slow down just because he may be crossing my path.
In fact, I may needlessly come to a complete stop to let him through, which entirely defeats the purpose of the roundabout, which is to prevent stick-shift drivers (see: 90% of Europe) from having to start from a complete stop.
so either I slow way down to allow myself to see all the possibilities in front of me (thereby inconveniencing myself and traffic behind me), or I barge through and get an unfortunate surprise.
at least at standard traffic lights, traffic making a left turn in front of straight-moving traffic has to yield.
How far in advance are you yielding, though? Assuming no other vehicles are present, if you both approach the roundabout at the same time, you can both enter at the same time. Even if the other driver enters first and is making a left, you don't have to yield to that driver till he gets around to your side of the roundabout. You yielding to circulating traffic only needs to happen when that vehicle could potentially be crossing your path if you were to enter.
A point to consider: With a roundabout, you may have to come to a complete stop upon entry. Once there's a gap in the circulating traffic, you can go. If there's nobody there, you never stopped--that can't always be said with an all-way stop or signal (assuming a law-abiding driver). One of the biggest benefits of roundabouts isn't the decrease in number of stops (which is a benefit in its own right), but the decrease in total delay.
You're supposed to indicate a right turn when you're about to exit the circle. So if you see no signal, you'd have to assume they're going to cross in front of you.
Doghouse left hand turn signals were scary to people back in the day. The concept of "Yield" is relatively new compared to Stop. They had to publish brochures to instruct people how to merge onto interstate highways. People can figure these things out. Just because it's new and different doesn't mean it shouldn't be done. If Europeans can figure out roundabouts, so can we.
Quote from: jjakucyk on March 25, 2010, 09:15:56 PM
You're supposed to indicate a right turn when you're about to exit the circle. So if you see no signal, you'd have to assume they're going to cross in front of you.
I think I've seen about 10% of US drivers do such a thing.
Quote from: agentsteel53 on March 25, 2010, 09:09:42 PM
Quote from: jjakucyk on March 25, 2010, 08:59:37 PM
People are supposed to use their turn signals to indicate when they're leaving the circle, and that would help with your situation.
which turn signal would they use when they are still coming towards me and have not made the turn, at which point it is obvious that they will cross in front of me? Left turn signal to indicate that their overall course is a left turn? Right turn signal to denote that they will exit at the next branch (which would be the branch directly opposite me)? Or, no turn signal, which could mean any number of things.
Right turn signal applied just before exiting the next branch, regardless of initial entry and final destination.
Generally, I find that using a turn signal in a roundabout is somewhat pointless. Although, the case can be made signaling an exit while in a multilane roundabout can be beneficial to the vehicle entering downstream, especially if the exiting driver is not in the outside lane.
Quote from: agentsteel53 on March 25, 2010, 09:09:42 PM
I've found that relying on drivers to behave logically is asking for trouble. Especially at roundabouts/rotaries/traffic circles. I barely know the difference, and likely could not recite all the right-of-way laws associated with each. The average driver doesn't even know that there's a difference - it's all a "big scary circle thing" - hold your breath and hope you make it out the other side.
You are totally right in this regard. Driving defensively is always important, cause you can never totally depend on the other driver to be rational, or to carry out something that is otherwise expected.
The main difference between a roundabout and a rotary/traffic circle is that roundabouts are always yield controlled with the entering traffic yielding. If a circle is stop or signal controlled, it's automatically a traffic circle by definition.
Quote from: roadfro on March 25, 2010, 09:13:46 PMif you both approach the roundabout at the same time, you can both enter at the same time.
Correct. I am assuming that he is just sufficiently "ahead" of me that he is already in the roundabout when I get to it, and he is just at the point where he is about to either exit (towards me) or continue onwards to make his left turn, at the precise time that I need to decide whether to slow down to yield to him, or speed up because he's harmless.
if (and that's a big if in the US) he indicates a right-turn signal for an exit, then neither of us slows down and the roundabout performs admirably. If I am stuck reading his "body language" as to whether or not he will exit, then I will guess "he will cross in front of me", and swear mightily to the heavens when he spontaneously exits.
I don't think in general American drivers consider the exit from a roundabout to be a
right turn that they need to indicate. I think they perceive it like an off-ramp from a freeway, which is another situation where technically one should indicate that they are exiting, but people only do so if they need to merge over from a lane that is not the furthest right in order to access the offramp.
in Boston, there will not be an indication forthcoming because the driver has checked that the merge is doable without anyone else's cooperation. No one there who needs to get out of the way.
in LA, there will not be an indication forthcoming because the driver is fairly sure that the merge is doable without anyone else's cooperation. Everyone should theoretically get out of the way in time.
in Miami, there will not be an indication forthcoming because the driver frankly doesn't care either way if the merge is doable. If you can't get out of the way, it's your fault for existing.
the only way roundabouts will ever work in Miami is if
everyone is issued a handgun, just to even the odds a bit.
Quote from: jjakucyk on March 25, 2010, 09:15:56 PM
You're supposed to indicate a right turn when you're about to exit the circle. So if you see no signal, you'd have to assume they're going to cross in front of you.
This only really works for large circles, though. For smaller "roundabouts", there isn't enough time between potential turnoffs to effectively signal right.
In these circumstances I sometimes see people signal left for what's overall a left turn. I'm 90% sure that's technically incorrect, but it's at least an understandable message.
Quote from: CL on March 23, 2010, 05:33:53 PM
Speaking of complex interchanges, does anyone see the usefulness of this monstrosity (http://i15core.utah.gov/InteractiveMap/) (click on exit 265 - Provo Center Street and then "design on" and zoom in)? Why in the world would they build that?? A simple diamond or SPUI interchange would suffice here, would it not? (As a side note that same project is building two diverging diamonds)
And, you can always close the circle and race on it.
Paging NASCAR, paging NASCAR. :-D