Traffic circle lane use

[empirestate]

What's the proper lane usage at this (non-modern) traffic circle? In particular, when would you use the inner lane of the circle? It seems that any movement–right, left, or U-turn–can be made from the outer lane of the circle, which is fed by the left lane of the approach roadways.

Now, compare and contrast with this nearby circle, where it appears that two lanes of approach feed into two lanes of circle for all movements. Why is this one different, and how is this configuration supposed to be navigated?

Finally, how does both of these differ from a properly configured multi-lane modern roundabout?


iPhone

[peterj920]

http://www.virginiadot.org/info/resources/round/Differences_between_Modern_Roundabouts_and_Old_Traffic_Circles.pdf

Above is a comparison chart between a rotary and a modern roundabout.  The rotaries you listed have a bigger center circle than a modern roundabout, there aren't any pre-determined lane designations before entering, and there is constant weaving in a rotary compared to a modern roundabout.   Roundabouts can be configured in many different ways based on traffic patterns.  In De Pere, WI a roundabout was reconfigured after being constructed because traffic was heavier than expected from the south leg.  Most of the traffic was going west across the bridge and there was previously only one lane that could go west.  After the reconfiguration, the left lane went west, and the right lane could go west, east, or north.  Here is a screenshot from google maps.  There was a flyer informing of the changes but I can't find it.  You can use screenshots from the past to see how the roundabout was previously configured.

https://www.google.com/maps/@44.4462962,-88.060539,3a,75y,18.77h,80.03t/data=!3m6!1e1!3m4!1sCem8TfYT3SzT6YgGRtmR5Q!2e0!7i13312!8i6656?hl=en

[empirestate]

http://www.virginiadot.org/info/resources/round/Differences_between_Modern_Roundabouts_and_Old_Traffic_Circles.pdf

Above is a comparison chart between a rotary and a modern roundabout.  The rotaries you listed have a bigger center circle than a modern roundabout, there aren't any pre-determined lane designations before entering, and there is constant weaving in a roundabout compared to a rotary.

Your chart says the reverse: that rotaries have a lot of weaving, whereas it's minimized in modern roundabouts. Also, the examples I linked to do have lane assignments given on approach signage: basically, the first exit is assigned to the right lane while any subsequent exits are assigned to the left lane. That's similar to how I've seen modern roundabouts signed as well.

As for other differences in geometry, speed, size, etc., I'm not really looking at that. I'm interested in how you actually navigate the roundabout, via which lanes, depending on where your planned exit is. The first one I linked seems to have an inner lane on the circular roadway that has no function as far as navigating through the circle; what's it for? And the second one has two lanes in the circle that are fed by two lanes on the approach; how does one drive through the circle if, say, I want to enter from the left lane and then take the third exit, also from the left lane? Stuff like that.

[johndoe]

I think Peter had a typo; you're not ever supposed to change lanes within a roundabout.  I think the intention of the inner lane is to allow for lane changes (which is ok in rotaries and traffic circles).

Where I'm fuzzy on traffic circles is the case where there are more departure lanes than the circle allows.  Your first example doesn't fall into this category; the right exiting lane is the previous right turn bypass.  But in your second example, why do those exits need two lanes?  Since the circle is striped concentrically (which is really the problem) only the outside lane can exit legally (I think... not 100% on this) .

If it's not clear to us, how is the public supposed to know when lane changes are allowed and when they're not? IMO there should never be an entire circle of concentric intermittent marking, and lane changing should be made illegal in all of these intersections.

[realjd]

They could fix both of those examples with some easy restriping to not make them terrible.

[empirestate]

Where I'm fuzzy on traffic circles is the case where there are more departure lanes than the circle allows.  Your first example doesn't fall into this category; the right exiting lane is the previous right turn bypass.  But in your second example, why do those exits need two lanes?  Since the circle is striped concentrically (which is really the problem) only the outside lane can exit legally (I think... not 100% on this) .

If it's not clear to us, how is the public supposed to know when lane changes are allowed and when they're not? IMO there should never be an entire circle of concentric intermittent marking, and lane changing should be made illegal in all of these intersections.

Yes indeed, the second circle (Bear Mountain Bridge Circle) suffers from the confusion of two lanes in, two lanes out, combined with the fact that traffic flow through the circle is subject to peak volumes and lopsided traffic counts on its approaches. In particular, through traffic from the Palisades Parkway onto the Bear Mountain Bridge tends to gum up those respective entrance and exit points, and makes yielding to traffic already in the circle an exercise in futility. Finally, the toll gate of the bridge being right by the circle, and the need for unsuspecting cash users to merge right (because the left toll lane is E-ZPass only) cause further backups.

But, assuming that traffic is light and free-flowing, what is theoretically the "correct" way to drive through this circle, using both lanes to their intended extent?

They could fix both of those examples with some easy restriping to not make them terrible.

What would that look like? Anybody care to whip up a little diagram?

[Tom958]

What would that look like? Anybody care to whip up a little diagram?

I don't, mainly because I don't do diagrams, but partly because the Bear Mountain Bridge circle is about as generic as it gets as far as overall layout. Without looking very hard, I found this roundabout in Michigan: four legs, each striped for two lanes at each entry and each exit. Hopefully it's not one of the ones that tradephoric was so concerned about-- more on that below.

One big difference is that the Michigan example is painted to unambiguously give two lanes to traffic exiting the roundabout, through the use of both solid and dotted lines, including thick dotted lines across the entries. Standard lane marking are not used within the roundabout or on its approaches or exits. In Streetview it appears that the pavement markings are nearly perpendicular enough to the path of entering traffic that they appear rightly irrelevant until a driver is within the circle. In the New York examples, though, the circles are bigger and thus the striping is viewed from a flatter angle, so it isn't as obvious what a driver who wishes to proceed straight or left is supposed to do. Also, the striping suggests that motorists should treat the lanes within the circle as they would treat lanes anywhere else, which isn't the case in a roundabout. Compare this to this. See what I mean?

That said, a smaller circle might lead to higher accident rates. 

Another difference is that the New York examples have overhead signage indicating that each exit is only one lane, and implying that traffic continuing to a subsequent exit needs to be in either the left or right lane of the circle when in fact straight-through traffic can and should use both lanes. With the way the various routes run through the Bear Mountain circle, overhead signage seems necessary, but it needs to be done in such a way as to not confuse drivers as to how to drive the circle.

[ScottRAB]

Lane changes in modern roundabouts is frowned upon, and depending on the lane markings may be illegal.  The entry signs and lane markings tell you what you can do and what lane to be in before entry based on where you want to go, just like any large multi-lane intersection.

   Many people confuse other and older styles of circular intersections with modern roundabouts.  East coast rotaries, large multi-lane traffic circles (Arc D'Triomphe, Dupont Circle), and small neighborhood traffic circles are not modern roundabouts.   If you want to see the difference between a traffic circle, a rotary (UK roundabout) and a modern roundabout (UK continental roundabout), go to http://tinyurl.com/kstate-RAB  to see pictures.   And here's another site that shows the difference between an older rotary and a modern roundabout: http://tinyurl.com/bzf7qmg

Modern roundabouts are the safest form of intersection in the world. 
The safety comes from the "˜slow and go' operation instead of the "˜stop or go fast' way a stop light works.  The smaller size of properly designed modern roundabouts is what makes them safer and keeps speeds in the 20 mph (30 kph) range.  This makes it much easier to avoid a crash or stop for pedestrians.  It also means that if a crash happens the likelihood of injury is very low. 
Safety is the #1 reason there are over 3,200 modern roundabouts in the US today and many more on the way.
Visit http://tinyurl.com/iihsRAB for modern roundabout FAQs and safety facts.  Modern roundabouts, and the pedestrian refuge islands approaching them, are two of nine proven safety measures identified by the FHWA, http://tinyurl.com/7qvsaem
   The FHWA has a video about modern roundabouts on Youtube, or check out the IIHS video (iihs dot org). 

http://priceonomics.com/the-case-for-more-traffic-roundabouts/

[empirestate]

Many people confuse other and older styles of circular intersections with modern roundabouts.  East coast rotaries, large multi-lane traffic circles (Arc D'Triomphe, Dupont Circle), and small neighborhood traffic circles are not modern roundabouts.   If you want to see the difference between a traffic circle, a rotary (UK roundabout) and a modern roundabout (UK continental roundabout), go to http://tinyurl.com/kstate-RAB  to see pictures.   And here's another site that shows the difference between an older rotary and a modern roundabout: http://tinyurl.com/bzf7qmg

Yeah, we've definitely covered the differences quite thoroughly in the forum, as well as the confusion in terminology.

Is there anything you'd like to offer with regard to these specific examples? They're older traffic circles, so pretend for a moment there's no such thing as modern roundabouts; upon encountering these configurations, how do you go about negotiating them? Are there other examples of old-style traffic circles that can give us clues about the intended lane use here?

[roadman65]

Circle, rotary, and a roundabout!  I guess its where you grew up with has the terminology.

In New Jersey we always called them circles and the signs leading into them were calling them that too.  In  Massachusetts when I was small  I remember upon entering the configuration seeing a big giant white on black arrow with the letters "ROTARY" within it.  It made my dad see the difference and say "How about that, up here they say Rotary instead of like home where its a simple circle."

True the terminology may have different meanings, but slang of local areas is might verses right in names.  For example in New York a Freeway is called an Expressway, even though both have different definitions.  Then a Parkway is a word used for "No Trucks and Busses" but a freeway with the exception of the Taconic and Saw Mill Parkways which really are expressways by definition.

[GaryV]

... I found this roundabout in Michigan: four legs, each striped for two lanes at each entry and each exit.

I've been through some like that, and survived, but I still don't know how they work.  Look at the dark car coming from the south.  He's in the left lane, and his pavement markings indicate he can go 1/2 or 3/4 around the circle.  But if he was 2-3 seconds sooner to the circle, he'd be right in the place where the blue car is entering from the east.  How would the blue car know that the dark car is or isn't going to cut across his path?

If that isn't bad enough, there's one at Van Dyke Ave and 18-1/2 Mile Rd in Sterling Heights (near the south end of the M-53 "Van Dyke" Freeway) that has 3 lanes in the roundabout.  I try to avoid that completely.

[jakeroot]

What would that look like? Anybody care to whip up a little diagram?

Here you go. You'd have to cut into the top entry leg a little to squeeze in the third lane. But you can pretty much make a turbo roundabout of any size with three entry lanes. I don't agree with roundabouts of this size, but they still operate in a similar manner, though the speeds are much higher. Not sure if that makes it more dangerous, but I know there's this perception that high speeds are usually bad.

... I found this roundabout in Michigan: four legs, each striped for two lanes at each entry and each exit.

I've been through some like that, and survived, but I still don't know how they work.  Look at the dark car coming from the south.  He's in the left lane, and his pavement markings indicate he can go 1/2 or 3/4 around the circle.  But if he was 2-3 seconds sooner to the circle, he'd be right in the place where the blue car is entering from the east.  How would the blue car know that the dark car is or isn't going to cut across his path?

He would know by waiting and seeing. That's how roundabouts work?

[roadman65]

The perfect circle using lanes are that in Asbury Park, NJ at NJ 35, NJ 66, and Asbury Avenue.  The lanes may not be striped ones, but look at the ends of the circle as its got two go around roads ( I am not sure what the geometrical word is for the end of the circle and I do not want to guess at it either). 

In essence it controls the traffic flow.  Its really two circles in one, as the inner circle allows WB to SB and EB to NB movements while the outer circle allows SB to EB and NB to WB.  Basically it acts the same as the OP.
https://www.google.com/maps/@40.2256908,-74.0361236,17z

[jakeroot]

The perfect circle using lanes are that in Asbury Park, NJ at NJ 35, NJ 66, and Asbury Avenue.  The lanes may not be striped ones, but look at the ends of the circle as its got two go around roads ( I am not sure what the geometrical word is for the end of the circle and I do not want to guess at it either). 

In essence it controls the traffic flow.  Its really two circles in one, as the inner circle allows WB to SB and EB to NB movements while the outer circle allows SB to EB and NB to WB.  Basically it acts the same as the OP.
https://www.google.com/maps/@40.2256908,-74.0361236,17z

I don't know if I'd call that a traffic circle. It's more like a gyratory; several one-way roads which funnel traffic around a central island, but without the smoothness of a perfect circle nor the rules of a roundabout. I'm personally okay with this design of roadway. There's the potential for more collisions, no doubt, as no one really has to stop. But it seems as though this design is able to control a lot more cars than a signal, or maybe even a smaller roundabout.

[roadman65]

Well my ex boss from years ago lived in Asbury Park, and it is considered a traffic circle despite its unusual design.  At least it separates traffic well as the two loops separate traffic real well.  The official name by NJDOT and area residents is the "Asbury Park Circle."

[empirestate]

What would that look like? Anybody care to whip up a little diagram?

Here you go. You'd have to cut into the top entry leg a little to squeeze in the third lane. But you can pretty much make a turbo roundabout of any size with three entry lanes. I don't agree with roundabouts of this size, but they still operate in a similar manner, though the speeds are much higher. Not sure if that makes it more dangerous, but I know there's this perception that high speeds are usually bad.

Neat; so on each approach, the right lane can go right, the middle lane can go right or left, and the left lane can go left or U. Could there be a version of this that doesn't add a third lane? Or would that just be a standard roundabout (right lane goes right or left; left lane goes left or U)?

... I found this roundabout in Michigan: four legs, each striped for two lanes at each entry and each exit.

I've been through some like that, and survived, but I still don't know how they work.  Look at the dark car coming from the south.  He's in the left lane, and his pavement markings indicate he can go 1/2 or 3/4 around the circle.  But if he was 2-3 seconds sooner to the circle, he'd be right in the place where the blue car is entering from the east.  How would the blue car know that the dark car is or isn't going to cut across his path?

He would know by waiting and seeing. That's how roundabouts work?

Yeah, I mean the car from the east would have to yield to him regardless of whether their paths cross or merge.

[Tom958]

... I found this roundabout in Michigan: four legs, each striped for two lanes at each entry and each exit.

I've been through some like that, and survived, but I still don't know how they work.

I've been thinking of writing this for years, and tonight's the night. 

Consider the intersection of Windy Ridge Parkway (you're on it in this view) and Windy Hill Road (crossing left-right) in suburban Atlanta. It's not a roundabout. This is in an upmarket office park where the developers made use of the hilly, heavily wooded terrain by building the main roads as pairs of two lane, one way roads with wide, forested medians. Pretty nice, isn't it? Traffic volumes are low enough not to require signalization (it would be daft to build something like this unless it was certain never to need signalization!), and, in fact, while it was once controlled by stop signs in all four directions, now Windy Hill Road doesn't stop. But, for purposes of illustration, let's look at when it had stop control in all directions.

First, where were the stop signs? Well, that's easy: only one is needed at each entry, as seen in the Streetview. If you're turning right, just stop at the stop sign, check to the left and go when the way is clear.

If you're going straight, stop at the stop sign, check to the left, realize (obviously) that there'll be no oncoming traffic since you're clearly on a one way roadway, then go when the way is clear. When you get to the next crossing, traffic from the right will have a stop sign just as you just did, and there'll be no traffic from the left because it's one way headed to the left. So, GO!  And, stating the obvious, it doesn't matter which lane you're in to go straight.

If you're turning left, you need to be in the left lane (duh!), preferably before you reach the stop sign. Just as for going straight ahead, you can pass through the first crossing after the stop sign without interference. That also means that you can turn left into either the left or right lane, because unless some dipshit is running the stop sign or turning left from the right lane at the same time you're turning left, there'll be no interference And leaving the intersection at the next crossing, there will again be no interference. You're home free.

That was fun. Now, what does it have to do with roundabouts? Quite a lot, I think. A roundabout is circular instead of square, and the entries are curved and have yield signs instead of being straight and having stop signs. But, you'd drive the two intersections the same way. More to the point, I hope: There's no good reason to get all paranoid because the road ahead of you is a little bit different in shape. Yield still means yield, pavement markings mean what they mean, and if you pay attention you can be in the lane you want to be in when you leave the roundabout.

[realjd]

The perfect circle using lanes are that in Asbury Park, NJ at NJ 35, NJ 66, and Asbury Avenue.  The lanes may not be striped ones, but look at the ends of the circle as its got two go around roads ( I am not sure what the geometrical word is for the end of the circle and I do not want to guess at it either). 

In essence it controls the traffic flow.  Its really two circles in one, as the inner circle allows WB to SB and EB to NB movements while the outer circle allows SB to EB and NB to WB.  Basically it acts the same as the OP.
https://www.google.com/maps/@40.2256908,-74.0361236,17z

I don't know if I'd call that a traffic circle. It's more like a gyratory; several one-way roads which funnel traffic around a central island, but without the smoothness of a perfect circle nor the rules of a roundabout. I'm personally okay with this design of roadway. There's the potential for more collisions, no doubt, as no one really has to stop. But it seems as though this design is able to control a lot more cars than a signal, or maybe even a smaller roundabout.

If you actually draw out the lane use of a roundabout, then warp the center island into a square, it's identical to 4 one way roads that intersect each other.

[jakeroot]

The perfect circle using lanes are that in Asbury Park, NJ at NJ 35, NJ 66, and Asbury Avenue.  The lanes may not be striped ones, but look at the ends of the circle as its got two go around roads ( I am not sure what the geometrical word is for the end of the circle and I do not want to guess at it either). 

In essence it controls the traffic flow.  Its really two circles in one, as the inner circle allows WB to SB and EB to NB movements while the outer circle allows SB to EB and NB to WB.  Basically it acts the same as the OP.
https://www.google.com/maps/@40.2256908,-74.0361236,17z

I don't know if I'd call that a traffic circle. It's more like a gyratory; several one-way roads which funnel traffic around a central island, but without the smoothness of a perfect circle nor the rules of a roundabout. I'm personally okay with this design of roadway. There's the potential for more collisions, no doubt, as no one really has to stop. But it seems as though this design is able to control a lot more cars than a signal, or maybe even a smaller roundabout.

If you actually draw out the lane use of a roundabout, then warp the center island into a square, it's identical to 4 one way roads that intersect each other.

I think they call those "Town Square intersections".

[empirestate]

I've been thinking of writing this for years, and tonight's the night. 

Consider the intersection of Windy Ridge Parkway (you're on it in this view) and Windy Hill Road (crossing left-right) in suburban Atlanta.

[...]

That was fun. Now, what does it have to do with roundabouts? Quite a lot, I think. A roundabout is circular instead of square, and the entries are curved and have yield signs instead of being straight and having stop signs. But, you'd drive the two intersections the same way. More to the point, I hope: There's no good reason to get all paranoid because the road ahead of you is a little bit different in shape. Yield still means yield, pavement markings mean what they mean, and if you pay attention you can be in the lane you want to be in when you leave the roundabout.

That's a great way to look at it. Now, how does that description jive with the two-in, two-out setup of the Bear Mountain Bridge Circle (my second example in the OP)? Specifically, if I'm in the left lane within the circle, and planning to exit to the left lane of one of the roadways, should I be assured of no conflict with traffic in the right lane that is continuing around the circle? Because I don't feel confident of that.

[jakeroot]

I've been thinking of writing this for years, and tonight's the night. 

Consider the intersection of Windy Ridge Parkway (you're on it in this view) and Windy Hill Road (crossing left-right) in suburban Atlanta.

[...]

That was fun. Now, what does it have to do with roundabouts? Quite a lot, I think. A roundabout is circular instead of square, and the entries are curved and have yield signs instead of being straight and having stop signs. But, you'd drive the two intersections the same way. More to the point, I hope: There's no good reason to get all paranoid because the road ahead of you is a little bit different in shape. Yield still means yield, pavement markings mean what they mean, and if you pay attention you can be in the lane you want to be in when you leave the roundabout.

That's a great way to look at it. Now, how does that description jive with the two-in, two-out setup of the Bear Mountain Bridge Circle (my second example in the OP)? Specifically, if I'm in the left lane within the circle, and planning to exit to the left lane of one of the roadways, should I be assured of no conflict with traffic in the right lane that is continuing around the circle? Because I don't feel confident of that.

The way Europe tends to do it is to determine which lanes do what with arrows on the pavement, prior to entering the roundabout. So even if the lanes are "concentric" within the roundabout itself, they are only painted to delineate between the inside and outside lane, not to direct traffic to their exits. In this manner, traffic has to have some basic understanding of the layout of the roundabout. So diagrams would be absolutely essential prior to the roundabout itself so traffic knows what is considered "straight" and what is considered "left" or "right".

Here's how this situation might be signed in the UK:

Note that, despite any markings at the roundabout, the left lane must turn left at the roundabout. And you know the layout of the junction by the diagram on the left.

In some cases, roundabouts are so complicated that markings are foregone with altogether. You only know what to do in the roundabout based on markings prior to the roundabout. In theory, this is no different than intersections without guide lines. You know what to do based on arrows and signs prior to the intersection. The curve in the roundabout just throws people off.

[roadman65]

There is one on Dyer Boulevard in Kissimmee at the entrance to a shopping center and a subdivision just north of the Osceola Parkway.  It has lane control and signs informing you which lane to use entering the circle, or should I say roundabout in this case as its too small, and of course Florida which has been coining this concept lately and using that name to call it by for ages now.

[realjd]

The perfect circle using lanes are that in Asbury Park, NJ at NJ 35, NJ 66, and Asbury Avenue.  The lanes may not be striped ones, but look at the ends of the circle as its got two go around roads ( I am not sure what the geometrical word is for the end of the circle and I do not want to guess at it either). 

In essence it controls the traffic flow.  Its really two circles in one, as the inner circle allows WB to SB and EB to NB movements while the outer circle allows SB to EB and NB to WB.  Basically it acts the same as the OP.
https://www.google.com/maps/@40.2256908,-74.0361236,17z

I don't know if I'd call that a traffic circle. It's more like a gyratory; several one-way roads which funnel traffic around a central island, but without the smoothness of a perfect circle nor the rules of a roundabout. I'm personally okay with this design of roadway. There's the potential for more collisions, no doubt, as no one really has to stop. But it seems as though this design is able to control a lot more cars than a signal, or maybe even a smaller roundabout.

If you actually draw out the lane use of a roundabout, then warp the center island into a square, it's identical to 4 one way roads that intersect each other.

I think they call those "Town Square intersections".

Interesting. That's exactly what I'm talking about. Traffic flow through a roundabout will be the same as a town square intersection where entering traffic (the road on the right at each crossing) is controlled by a yield sign.

[jeffandnicole]

The perfect circle using lanes are that in Asbury Park, NJ at NJ 35, NJ 66, and Asbury Avenue.  The lanes may not be striped ones, but look at the ends of the circle as its got two go around roads ( I am not sure what the geometrical word is for the end of the circle and I do not want to guess at it either). 

In essence it controls the traffic flow.  Its really two circles in one, as the inner circle allows WB to SB and EB to NB movements while the outer circle allows SB to EB and NB to WB.  Basically it acts the same as the OP.
https://www.google.com/maps/@40.2256908,-74.0361236,17z

I don't know if I'd call that a traffic circle. It's more like a gyratory; several one-way roads which funnel traffic around a central island, but without the smoothness of a perfect circle nor the rules of a roundabout.

In other words, a normal Jersey Traffic Circle! Don't forget about the other driveways mixed throughout the circle, creating many additional entry/exit points which requires traffic to unnaturally cross solid lines and lanes of traffic to reach them.  I think the best/oddest part of this circle is the little stub as traffic goes towards 66 West: https://goo.gl/maps/EZ3UWUh2xFx  It's not even lined to direct traffic into it.  The only sign is a mini arrow on the larger sign shown in the link.

Well my ex boss from years ago lived in Asbury Park, and it is considered a traffic circle despite its unusual design.  At least it separates traffic well as the two loops separate traffic real well.  The official name by NJDOT and area residents is the "Asbury Park Circle."

NJ signs it as a traffic circle as well...with one of the highest advisory limits one's gonna find going into a circle!  https://goo.gl/maps/p8HWwEeodnK2

[Tom958]

That's a great way to look at it. Now, how does that description jive with the two-in, two-out setup of the Bear Mountain Bridge Circle (my second example in the OP)? Specifically, if I'm in the left lane within the circle, and planning to exit to the left lane of one of the roadways, should I be assured of no conflict with traffic in the right lane that is continuing around the circle? Because I don't feel confident of that.

Yeah, I could understand that. I think it has do do with the pavement markings as they exist now versus proper roundabout markings that unambiguously show two lanes leaving the roundabout at every exit. That and your level of confidence in your fellow drivers, especially since there are badly-marked traffic circles and miseducated drivers in the area.

What you could do, if you're going (for example) southbound to eastbound: as you curve from the southward exit to head eastward, switch into the right lane of the roundabout, then switch back to the left lane after leaving the roundabout or at least after leaving the inscribed circle. That'd be as soon as it's safe and legal or almost legal. As explained above, there should be no interference as you move to the right lane, and it'd take real talent for anyone to obstruct your change back to the left.

Having said that: If a driver is at the northbound entry sees you in the left lane of the circle, he should realize that there's a good chance that you'll be taking the eastbound exit if you enter from the east and a certainty (unless you're Clark Griswald) if you enter from the north. So, he should stay out of your way. He should also stay out of your way if you're in the right lane. And, if he has no idea what you're doing and thinks you're a crazy nut, he should be extra triple sure to stay out of your way.