Category Archives: Roundabouts

Some Dutch roundabouts

Dutch roundabouts have received a lot of publicity, notably here:

Roundabout design in the Netherlands has seen a long process of trial and error. A design used until bicyclists complained strongly enough about it placed the bikeway away from the circular roadway, but cyclists were required to yield. Here is an explanation of Dutch roundabout design developments.

The current preferred design places the bikeway away from the circular roadway, and motorists are required to yield, as shown in this video below. That clears up yielding issues.

Here is a video of a roundabout outside the city of s’Hertogenbosch, put forward as an example of good design.

There is a long discussion of this roundabout, among others, on Facebook.

This is a rather large roundabout at the intersection of major highways, and with moderate deflection on entry or exit.  Looking here in Google Maps,  it’s clear that the highway in the background at the left is a bypass around the city of s’Hertogenbosch — though not a limited-access highway like the one which appears in the distant background in the video.

This roundabout was constructed in connection with the new bypass road around the city. Google Street View from 2009 shows the roundabout under construction. A sidelight on this observation is that Dutch practice does consider motor traffic. Two of the legs of the intersection at the roundabout are new roads being constructed at the same time.

I’ve been told by a knowledgeable person that the  bikeways on either side of the highways are supposed to be one-way, but the only destinations along these bikeways are at intersections — reducing the temptation to ride opposite traffic.

The design requires a lot of space because the circular bikeway is  much larger than the circular roadway. The roundabout  is outside a city, but nonetheless, it appears that several houses had to be demolished or moved to make way for this roundabout.

The installation here  places separate bikeways (red asphalt) and walkways (paver blocks) outside the circular roadway. Bicycle traffic shown in the video is light. If bicycle traffic were heavy, it would result in  congestion of motor traffic because motorists yielding to cyclists could not enter or exit the roundabout. Having a path (or for that matter, crosswalks) around the outside of a roundabout obviates the main advantage of the roundabout, that traffic can keep moving. Only grade separation would avoid this for both bicyclists and pedestrians. Motor vehicles and bicycles sharing the roadway would avoid the bicyclists’ causing congestion, but would not be as attractive for bicyclists lacking in skill and confidence..

If you look at the video full-screen, you can see a number of details which are not evident in the small window on this page. I am most interested in the interactions and negotiations for right of way, which are the central issue with mobility and safety in any intersection which is not traffic-signal controlled.

Expectation in the Netherlands is that motorists will yield wherever they see shark-tooth markings. The path around the outside of the roundabout is brought out to the entry and exit roads at a right angle and far enough outside the roundabout so that motorists will be able to see approaching bicyclists. Ohio resident Patricia Kovacs has investigated roundabouts in that state and demonstrated that motorists don’t even yield to pedestrians. She has posted some comments about roundabouts on this blog and in the Facebook thread mentioned earlier.

Some cyclists in the s’Hertogenbosch video are shown looking to their right as they pass paths coming in from their right, for example at 0:55 and 2:25, but many are shown not turning their heads to look for conflicting motor traffic. That is to say, they are putting their complete faith and trust in motorists to yield to them, which is a comment on Dutch expectations for motorist conduct. There is an especially stunning example of this at 1:59, where a cyclist powers through an intersection as motorists approach from the left, inside the roundabout, and the right, entering it. However, at 6:07, a motorist stops abruptly at an exit to the roundabout as a fast cyclist comes around from the right.

One cyclist leaves the roundabout on the left side, opposite the intended direction, at 1:38 in the video.  Another is riding around the roundabout clockwise at 2:40 and apparently while talking on a mobile phone.

At 2:34, a motorist is shown slowing to yield to a cyclist who turns right rather than to cross the exit of the roundabout. With no lane changing or negotiation betwen motorists and cyclists, the motorist did not have a way to know which way the cyclist would go.

Cyclists carry various objects in their hands or on the handlebars. At 6:40, a cyclist is carrying something which looks like a hockey stick.

At 7:18 a young woman has a disabled bicycle and is walking.

Now let’s look at some other Dutch roundabouts.

A roundabout inside s’Hertogenbosch, here,  has the bikeway immediately adjacent to the circular roadway, so that cyclists are hidden directly behind — not next to — exiting vehicles. The video shows motorists required to yield to cyclists in spite of this right-hook threat.

Here’s the video of the roundabout. Are the cycling facilities safe, as claimed? Or if safety is achieved here, is it maybe achieved in another way? You decide.

The description of the video indicates that this roundabout is rather new. Its design appears to be restricted by the small available space at an urban intersection.

Some notable interactions:

At 0:20, a car brakes rather abruptly. Shortly thereafter, a motor scooter passes through the roundabout on the roadway.

At 0:30 and again at 0:53, a car blocks the bikeway to allow a pedestrian to cross in a crosswalk which is just outside the bikeway.

Most bicyclists are not paying any attention to the traffic in the roundabout, At 0:45, a bicyclist is looking down at a cell phone, but at 0:50, 1:10, 1:29, 1:53, 2:03 and 2:10,  and a few additional times, bicyclists perform a shoulder check. The one at 2:03 does this while also carrying a cell phone in one hand.

At 1:49 and again at 2:20, there is a motorcycle in the bikeway, waiting along with bicyclists to enter the roundabout, and there is a bicyclist standing over his bicycle, facing opposite the direction of traffic.  It appears that he is having a conversation with the motorcyclist and a couple of pedestrians. They are blocking the crosswalk.

At 2:49, a motorist stops in the roundabout to yield to a bicyclist who does not cross, but instead turns right. The bicyclist gives a right-turn signal, but too late for the motorist to react, and in any case, a prudent motorist would not risk that the bicyclist would go straight even though signaling. The design of the roundabout does not make the bicyclist’s intentions obvious.

At 2:58, a bus barely outpaces a bicyclist through the roundabout. The bicyclist turns right, but the bus driver has no way to know that he will. The bus driver is either very highly skilled at judging the bicyclist’s speed, or reckless. The bicyclist would have had to yield to the bus if going slightly faster and continuing around the roundabout.

Starting at 3:00, several bicyclists enter traveling the wrong way on the bikeway or sidewalk. Some turn right but others pass close to a doorway which a pedestrian has just exited, and a blind corner, and cross from right to left in the crosswalk or bikeway. An articulated bus enters the roundabout and these bicyclists pass behind it. Other bicyclist traveling counterclockwise around the roundabout will have to yield to the long bus, though this occurs outside the field of view of the video.

At 3:45, bicyclists share the bikeway around the roundabout with a skateboarder and motor-scooter rider.

Almost all the bicyclists are pedaling about 40 rpm.

Here’s a roundabout where bicyclists go around square corners:

And a little roundabout with advisory bike lanes at some of the entrances:

In the so-called “shared space” roundabout in Drachten, cyclists share space with pedestrians. The meaning of the term “shared space” is very different here from its more usual meaning, that motorists, bicyclists and pedestrians all operate in the same space.  In the Drachten roundabout, bicyclists and pedestrians share space — as on shared-use paths in the USA — but are strictly separated from motor traffic except in crossings, as in the other Dutch roundabouts. The space around the margins of the Drachten roundabout also serves as a pedestrian plaza.

I’m poking around in YouTube and Google maps. Here’s a roundabout in YouTube — — location not given, as is usual in such promotions, but I found it in Google Maps by searching on the name of one of the businesses nearby: A special feature made the roundabout practical: the buildings are set far back at a 45-degree angle on each corner. The circular bikeway around the outside makes it possible for motorists to see cyclists in order to yield (though motorists don’t always, as the video shows) and greatly adds to space requirements, which already are large for a roundabout. There wouldn’t be room for such a roundabout at many urban intersections.

Here’s a blog post which includes the video just described and others of the same roundabout, and describes different types of Dutch roundabouts.

Another roundabout in Amsterdam is of the spiraling Turbo Roundabout design, with a path close around the outside and scary sight lines which place a cyclist too far to the right to be in view of a motorist exiting the roundabout: and street view, . Traffic signals have had to be placed at the exits to mitigate these conflicts. This is a triple roundabout with a tramway going around the inside, also requiring traffic signals.

The left and center roundabouts in this overhead view, also are of the bikeway around the outside type: but the rightmost one, in a wooded area, is of the newer type.

Dutch roundabouts are  of several types for motor traffic, but the major difference for bicyclists is whether they travel around the outside of the roundabout, or there are grade separations. There are no examples like the small modern roundabouts and neighborhood traffic circles in the USA, where bicyclists share the roadway with motor vehicles.

Here is an example of grade separation:

And here is a showcase example of grade separation — replacing an installation much like the one shown in the first video embedded in this post :

Roundabouts are expensive and take up a lot of space.  Many of the promotions we are seeing of Dutch facilities ignore these limitations and the compromises they exact and/or celebrate the newest and most impressive examples.

Change lanes in a roundabout?

Ohio cyclist Patricia Kovacs posted an e-mail asking some questions about roundabouts:

Ohio engineers are telling us to use the inner lane for left turns and U turns. Both the FHWA [Federal Highway Administration] and videos available on our local MPO [metropolitan planning organization] website say this. I shared this when we asked for updates to Ohio Street Smarts. If the FHWA and MORPC [Mid-Ohio Regional Planning Commission] are wrong, then we need to fix it.

Would you review the 8 minute video on the MORPC website and let me know what I should do? If it’s wrong, I need to ask them to update it. This video was made in Washington and Ohio reused it.

Looking further into the problem, I see a related practical issue with two-lane roundabouts, that the distance between an entrance and the next exit may be inadequate for a lane change. The larger the roundabout, the longer the distance in which to change lanes, but also the higher the speed which vehicles can maintain and so, the longer distance required. I’m not sure how this all works out as a practical matter. Certainly, turning right from the left-hand lane when through traffic is permitted in the right-hand lane is incorrect under the UVC [Uniform Vehicle Code], and results in an obvious conflict and collision potential, but I can also envision a conflict where a driver entering the roundabout does not expect a driver approaching in the inside lane of the roundabout to be merging into the outside lane.

All in all, the safety record of roundabouts is reported as good (though not as good for bicyclists and pedestrians), but I’m wondering to what extent the issues have been subjected to analysis and research. When I look online, I see a lot of roundabout *promotion* as opposed to roundabout *study*. Perhaps we might take off our UVC hats, put on our NCUTCD [National Committee on Uniform Traffic-Control devices] hats, and propose research?

Thanks, Patricia.

This post was getting long, so I’ve placed detailed comments on the Ohio video, and embedded the video, in another post. I’m also working on an additional post giving more examples, and I’ll announce it here when it is ready.

Here are some stills from the video showing the conflict between through traffic in the outer lane and exiting traffic in the inner lane.

First, the path for through traffic:

Path for through traffic in a roundabout

Path for through traffic in a roundabout

Next, the path for left-turning traffic:

Path for left-turning traffic in a roundabout

Path for left-turning traffic in a roundabout

Now, let’s give that picture a half-turn so the left-turning traffic is entering from the top and exiting from the right:

traffic in a roundabout, image rotated 180 degrees

Path for left-turning traffic in a roundabout, image rotated 180 degrees

And combining the two images, here is what we get:

Conflict between through traffic and exiting left-turn traffic

Conflict between through traffic and exiting left-turn traffic

The image below is from the Manual on Uniform Traffic Control Devices, and shows similar but not identical lane use. The arrows in the entry roadways direct through traffic to use either lane.

FHWA diagram of a roundabout with lane-use arrows.

FHWA diagram of a roundabout with lane-use arrows.

Drivers are supposed to use their turn signals to indicate that they are to exit from the inner lane — but drivers often forget to use their signals. Safe practice for a driver entering a roundabout, then, is to wait until no traffic is approaching in either lane, even if only entering the outer lane.

A fundamental conceptual issue here is whether the roundabout is to be regarded as a single intersection, or as a series of T intersections wrapped into a circle. To my way of thinking, any circular intersection functions as a series of T intersections, though it functions as a single intersection in relation to the streets which connect to it. Changing lanes inside an intersection is generally prohibited under the traffic law, and so, if a roundabout is regarded as a single intersection, we get the conflicts I’ve described.

Sometimes, dashed lines are used to indicate paths in an intersection, when vehicles coming from a different direction may cross the dashed lines after yielding right of way or on a different signal phase. More commonly, a dashed line  indicates that a driver may change lanes starting from either side. The dashed lines in a two-lane roundabout look as though they serve the second of these purposes, though they in fact serve the first. These are shorter dashed lines than generally are used to indicate that lane changes are legal, but most drivers don’t understand the difference.

That leads to confusion. If you think of the roundabout as a single intersection, changing from the inside to the outside lane is illegal anywhere. If you think of the roundabout as a series of T intersections, changing lanes should occur between the entries and exits, not opposite them –though there is also the problem which Patricia mentioned, that a small two-lane roundabout may not have much length between an entry roadway and the next exit roadway to allow for a lane change. That is, however, much less of a problem for bicyclists than for operators of wider and longer vehicles. It would be hard to construct a two-lane roundabout small enough to prevent bicyclists from changing lanes.

My practice when cycling in conventional two-lane traffic circles — and there are many in the Boston, Massachusetts area where I live — is to

  • enter from the lane which best leads to my position on the circular roadway — either the right or left lane of a two-lane entry;
  • stay in the outer lane if leaving at the first exit;
  • control the inner lane if continuing past the first exit;
  • change back to the left tire track in the outer lane to prepare to exit.

That way, I avoid conflict with entering and exiting traffic in the outer lane, and I am making my lane change to the right in the slow traffic of the circular roadway rather than on the straightaway following it. This is what I have found to make my interactions with motorists work most smoothly. Why should a bicyclist’s conduct in a roundabout be different?

It is usual to be able to turn right into the rightmost lane of a multi-lane rodway while raffic is approaching in the next lane. I don’t know of any other examples in road design or traffic law in the USA where a motor vehicle is supposed to turn right across the lane where another motor vehicle is entering it. Bike lanes are sometimes brought up to intersections, though the laws of every state except Oregon require motorists to merge into the bike lane before turning. The illustration below, from Dan Gutierrez, depicts the problem.

Right hook conflicts, from Dan Gutierrez's Understanding Bicycle Transportation

Right hook conflicts, from Dan Gutierrez’s Understanding Bicycle Transportation video and course.

Applicable sections or the Uniform Vehicle Code are:

  • 11:304 (b) — passing on the right is permitted only when the movement can be made in safety.
  • 11:308 (c) — a vehicle shall be driven only to the right of a rotary traffic island.
  • 11:309 (a) — no changing lanes unless it can be done in safety
  • 11:309 (d) — official traffic control devices may prohibit lane changes
  • 11:601 (a) Right turns – Both the approach for a right turn and a right turn shall be made as close as practicable to the right-hand curb or edge of the roadway.


How not to restripe

Gordon Renkes has produced a video showing conditions following restriping at Tamarack Circle in Columbus, Ohio, USA. Here’s a Google overhead view of this rather unusual circular street. Click away the caption balloon to get a better view. You may enlarge this view, or go to the full-featured Google page by clicking on “View Larger Map under the image.

View Larger Map

The teardrop pointer is at the location of the Google Street View below, of Tamarack Circle before the restriping. (I downloaded the image instead of embedding the Google image, in case Google redoes the Street View).

Google Street view of Tamarack Circle before restriping

Google Street view of Tamarack Circle before restriping

Before the restriping, with the very wide right lane, motorists probably parked most of the way to the corner, and many cyclists probably rode in the door zone.

Here’s the video showing condition following the restriping:

The design does encourage cyclists to ride outside the door zone of parked cars. But, as the video shows, the striping confuses motorists. Among other things, the striping instructs them to right-hook cyclists. In the video, one motorist even right-hooks another. Ohio law says:

“Approach for a right turn and a right turn shall be made as close as practicable to the right-hand curb or edge of the roadway.”

Striping which incites violations of the law risks liability claims.

Creating right-turn pockets to resolve the problems would require removal of a few parking spaces before each entering street.

If parking were on the left at the inside of the curve, sight lines at intersections with streets at the outside would be better (though worse at driveways at the inside, and for drivers exiting parking spaces, due to the curve). A combined bike lane/right turn lane (still “experimental”) would be needed due to width limitations.

In defense of neighborhood traffic circles

Nieghborhood traffic circle in Berkeley, California

Neighborhood traffic circle in Berkeley, California

In a post to an e-mail list, I made the statement:

On narrow streets in residential areas…small traffic circles at intersections can slow traffic and reduce the temptation to use those streets for through travel…

…which elicited the following response from Ken O’Brien, whom I consider a friend, but who is also probably the most hard-core supporter of equal treatment for bicyclists and motorists I know. He rejects all special treatments, including ones which I regard as beneficial.

I’m very disappointed to read John Allen supports these foolish structures.

These bogus structures encourage left turning and straight-through traffic to enter intersections swinging right (to avoid and go around the obstacle). They encourage traffic to perform lateral merges (and a lateral merge away from the direction they intend to travel) immediately at the intersection. They break the rule that you want traffic to prepare for lateral merges early and separately from scanning for conditions ahead immediately at the intersection.

Please, please Mr Allen, reconsider your support for these illogical attempts at traffic calming.

I responded:

I can always count on Ken O’Brien to make principled and consistent comments based on traffic theory, and I would agree with most of his comments if such structures were installed on streets with fast or heavy traffic. In fact, one of my complaints about the reconstruction at the rotaries on Concord Avenue in Cambridge [Massachusetts] was the narrowing of the travel lanes, resulting in some of the very problems he describes.

I think that Ken and I can agree that rotaries do not inherently defy the rules of good, simple intersection design. A rotary [the Massachusetts name; also, “traffic circle” and in its modern, improved version, “roundabout”] is a street with several other streets entering at T intersections from the right, and the T intersection is a very ordinary type of intersection.

Drivers must merge with traffic in the rotary and then go around to the desired exit. When Ken says that drivers must make “a lateral merge _away_ from the direction they intend to travel” — well, they intend to travel around the rotary, and so they are merging into the traffic flow of the rotary. As drivers enter the rotary, conflicting traffic comes from only one direction, the left, rather than from three directions as in a “crossroads” intersection. Once in the rotary, it comes from only one direction, the right. To this extent, I do not agree with Ken’s comments about traffic flow. True, traveling straight through or turning left is more complicated and slower in a rotary than at a “crossroads” intersection — if there is no conflicting traffic — but that fact does not imply any inherent disagreement with ordinary traffic rules.

Bicyclists are impeded by the small rotaries much less than motorists are. The only maneuver that is slower for a bicyclist is the left turn: a bicyclist must go around the rotary to make a left turn. Because of the narrowness of a bicycle compared with motor vehicles (other than motorcycles), the small rotary does not slow a bicyclist’s travel at all for through travel or right turns.

Ken says that the small rotaries that “break the rule that you want traffic to prepare for lateral merges early and separately from scanning for conditions ahead immediately at the intersection.”

Actually, as these rotaries are typically on two-lane, two-way or one-lane, one-way streets, they don’t require any merges at all before the intersection, except by operators of slow, narrow vehicles such as bicycles. A bicyclist should merge into the traffic flow before going around the rotary, but then a bicyclist should do this for through travel at any rotary [and at many if not most other intersections]. The merge is particularly easy at the small rotaries because motorists, with their need to steer right around the center island, must slow to bicycle speed before entering the rotary. I’ve been in Berkeley [California] repeatedly and ridden through such rotaries, and I did not get the uneasy feeling I always get with bikeway junctions which defy the rules of traffic flow, the feeling that drivers, including me, need to have eyes in the back of our heads or X-ray vision to see traffic that might conflict with the movements we are preparing.

Now let’s step back a bit and look at the larger issue of reduction of traffic speed and volume in residential neighborhoods.

Wherever residential streets provide useful shortcuts or alternative routes, and especially in cities like Berkeley with a grid traffic pattern, use of residential streets by through motor traffic becomes a nuisance and a hazard. Residents demand a solution. What solutions are available?

Attempting to ban non-resident motorists would be unworkable, and a violation of the basic right of free travel. Location-specific electronic monitoring and control of vehicle speeds is an idea whose time has not yet come. Low speed limits and traffic-law enforcement can work if they have enough political support, but budgets for law enforcement are often inadequate, and while residents want to prevent speeding in their own neighborhoods, they want to avoid speeding tickets in other neighborhoods. Everyone has only one own neighborhood but there are many other neighborhoods, and so the political force to weaken enforcement usually wins out. We’ve seen this happen recently with challenges to photo-monitoring and ticketing of speeding motorists.

Because the “soft” measures aren’t very effective, residents demand, and you will find, some form of traffic calming in almost any residential neighborhood. Then the question becomes: what form of traffic calming?

The “spaghetti” pattern of curved streets in many newer suburban developments? Well, that can’t be retrofitted onto existing neighborhoods, and it’s confusing too — getting lost on the curved streets is very easy. Cul de sac development patterns? They force everyone including bicyclists to take long, roundabout routes on major arterials. Conflicting one-way signs from one block to the next (a favorite approach in the Boston, Massachusetts area)? That’s good at reducing the traffic volume on the residential streets, but works sorely to the disadvantage of bicyclists.

Bicycle-permeable barriers and diverters to break up through routes? Berkeley has some of these and I think they have their place, but they also can pose hazards if they result in nonstandard traffic movements, and they pose an issue of quick access for emergency vehicles. Speed humps and speed tables? I think they also have their place, but they do pose the issue of possible damage to vehicles. Bulb-outs, narrowing of the travel way, chicanes (making the traveled part of the street weave from one side to the other, for example by alternating parking on one side and then the other)? I think these measures have their place too, but they can work sorely to the disadvantage of bicyclists if the travel way is excessively narrowed. Snow clearance also becomes more difficult as the street gets more complicated.

All in all, I think that for bicyclists, the small rotaries are one of the least disadvantageous and most advantageous forms of traffic calming. By preventing motorists from traveling through intersections at high speed, the small rotaries succeed in reducing the speed and volume of traffic on the residential streets very substantially. Through-traveling motorists are discouraged from using these streets and are more likely to use arterial streets instead.

I’m sure that the success of the rotaries depends on design details; in particular, the traffic island must be large enough to accommodate the turning radii of vehicles that use the intersection. Success also depends on location. I have indeed seen one such rotary that failed — installed on Concord Street in Wellesley Lower Falls, Massachusetts and was made of collapsible, reflectorized poles. I wish I had a photo of it, but vehicles damaged it and it had been removed within a few weeks, before I got back to it with a camera.

Concord Street, which becomes Park Street in Weston, is a minor arterial street with a connection at each end to a numbered state highway and another connection in the middle to the Massachusetts Turnpike. As much as residents living along this street might have wanted otherwise, the needs and desires of through-traveling motorists prevailed. The small rotaries in Berkeley, on the other hand, do appear to have succeeded.

Davis, California historical documents

Thanks to John Ciccarelli, Robert Sommer and David Takemoto-Weerts — and David’s students — among others — I am able to post online a number of documents about bicycling in Davis, California and the Davis bicycle program. Davis has the longest experience with a bicycle program of any city in the USA, and a large population of cyclists thanks to its being the home of the University of California at Davis.

You may surf to my table of contents page for the Davis documents and a complete list of people I have to thank — but also please read the rest of this post:

Of particular note are the conclusions which Davis has reached about different types of bicycle facility designs. Davis pioneered some brilliant design innovations, for example, bicycle traffic circles. On that topic, also see videos here and here.

Davis also has been willing to learn from mistakes and move onward. In another post, I have assembled quotes about Davis’s experience with barrier-separated bike lanes, versus conventional bike lanes separated from the adjacent lane only by a painted stripe, an issue which is particularly relevant as I write this in 2010.