Category Archives: traffic circles

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.

Dr. Furth’s and his students’ plan for South Brookline

On March 14, 2011, I attended a meeting in Brookline, Massachusetts, a suburb of Boston. At that meeting, Dr. Peter Furth of Northeastern University, and some of his students, gave a presentation on proposals for street reconstruction and bikeways in the southern part of Brookline.

Proposed treatment for West Roxbury Parkway

Proposed replacement of two two-lane one-way roadways with shoulders by a narrowed two-way roadway without shoulders and an adjacent multi-use path; Newton Street (up the embankment at the left) to provide local access only.

Most of the streets in the project area are fine for reasonably competent adult and teen cyclists to share with motorists, though one street, Hammond Street, is much less so, with its heavy traffic, four narrow lanes and no shoulders. I do agree with a premise of the presentation, that bicycling conditions could be improved, but I suggest different treatments, such as conversion from four lanes to three, with a center turn lane which becomes a median at crosswalks, also freeing up room at the sides of the roadway for motorists to overtake bicyclists.

Please read through this introduction before looking through the photo album I have posted with images from the meeting presentation, and drawings which were taped up in the meeting room.

My Concerns with the Proposal

Generally, I am concerned with the hazards and delays — and in winter, complete lack of service — which the proposal introduces for bicyclists, and with the blockages and longer trips it introduces for motorists, resulting in delay and in increased fuel use and air pollution. Some specifics:

  • The proposed system of narrow two-lane streets and segregation of bicyclists onto parallel paths makes no provision for the foreseeable increasing diversity of vehicle types and speeds as fuel prices rise. This trend can only be managed efficiently and flexibly with streets that are wide enough to allow overtaking.
  • Proposed paths are on the opposite side of the street from most trip generators, and many movements would require bicyclists to travel in crosswalks, imposing delay, inconvenience and risk for bicycle travel on the proposed route and on others which cross it. Small children would not safely be able to use the proposed routes unless accompanied by an adult, same as at present.
  • The proposal would further degrade or eliminate bicycle access in winter, because of the proposed 22-foot roadway width, and because the proposed parallel paths could not be kept ice-free even if they are plowed.
  • Though intersections are key to maintaining traffic flow, the proposal puts forward an incomplete design for most intersections and no design for some of them.
  • The narrowed streets provide no accommodation for a vehicle which must stop while preparing to turn left into a driveway, or to make a delivery, or to pick up or discharge passengers, for bicyclists who must travel in the street to reach a destination on the side opposite the path, or for bicyclists who wish to travel faster than the path allows.
  • The proposal includes no discussion of improvements to public transportation, which would be key to reductions in congestion and fossil fuel use. There are no bus turnouts, although Clyde and Lee Streets are on an MBTA bus line, school buses use the streets in the project area, and additional bus routes are foreseeable.
  • The proposal includes a 12-foot-wide service road along Clyde and Lee Street, part of which is to carry two-way motor traffic along with bicycle and pedestrian traffic. At times of heavy use, 12 feet on the Minuteman Bikeway in Boston’s northwestern suburbs is inadequate with only pedestrian and bicycle traffic. 12 feet is not wide enough to allow one motor vehicle to pass another. Larger service vehicles (moving vans, garbage trucks etc.) could access parts of this service road only by backing in, or by driving up a curb and across landscaped areas. These vehicles would completely block other motorized traffic on the service road.
  • The proposal is expensive because it requires tearing up every one of the streets in order to narrow it, not only construction of a parallel path.

Confusion in the Presentation

There also was confusion in the presentation:

  • North is confused with south, or east with west in the captions to several photos. Due to the confusion, some photos show a path on the opposite side of the street from where the plan drawings place it.
  • Some items in the illustrations are out of proportion. In one illustration (the one near the top in this post), a two-lane arterial street is only 10 feet wide, based on the height of a Segway rider on an adjacent path, or else the Segway rider is 12 feet tall, riding a giant Segway.
  • Other details are inconsistent, for example, showing a sidewalk in a plan drawing, but no sidewalk in an image illustrating the same location.
  • There is confusion about location of some of the photos. Some cross-section drawings are shown without identification of the location in the plans. The location of one cross section is misidentified.
  • The proposal makes unsupportable claims about safety.

There also is an ethical issue: in their presentation, the students have appropriated a number of Google Street View images without attribution — a violation of copyright and of academic ethics. (Furth’s students also plagiarized photos from my own Web site for a different presentation, but I digress.)

Overview and Conclusions

The proposal generally attempts to make bicycle travel a safe option for children and for people who are new to bicycling. It fails to accomplish that, due to problems with access across streets to the proposed pathways. It also adds complication and delay for motorists and for the majority of existing and foreseeable bicycle users. It degrades and sometimes eliminates bicycling as an option in the winter months, and it pays no attention whatever to public transportation.

I have no objection to construction of a path in the parkland adjacent to the streets in the project area, but the proposal also works to enforce the use of the path by reducing the utility of the road network for bicyclists as well as for other users.

I do think that street improvements are desirable, and on one street (Hammond Street) a high priority to improve bicycling conditions, but these improvements can be achieved mostly through restriping, without the massive reconstruction, or rather, deconstruction, that has been proposed.  This narrowing the roadways is intended to increase greenspace, and also  apparently to reduce speeding, but the proposal goes way overboard in reducing capacity, convenience and flexibility. There are other options to reduce speeding, most notably enforcement and traffic-calming measures which affect speed without decreasing capacity.

The large multi-way rotary intersection of  Hammond, Lagrange and Newton Streets, West Roxbury Parkway and Hammond Pond Parkway is the one place where I consider reconstruction to be a high priority.

Education also is an essential element of any attempt to make bicycling safer and a more practical option.

Larger Contextual Issues

Long-run issues of energy cost and availability raise questions about the viability of sprawled suburbs whose residents are dependent on private motor-vehicle travel.

South Brookline is more fortunate. It is a medium-density residential area of single-family homes, only about 5 miles from the Boston city center and also only a few miles from the Route 128 corridor, a major employment concentrator. Schools, places of worship, parklands and shopping are closer than that. Bicycling can and should have a role here, but for many people and many trips, it is not an option, due to age, infirmity, distance, and the need to transport passengers and goods.

South Brookline could benefit from a comprehensive transportation plan, including strengthening of public-transportation options and maintaining arterial roads with capacity for varied existing,  foreseeable and unforeseen uses.

Developing such a plan requires skills, resources and time beyond what I can muster, and so I’ll not attempt that here.

Now, please move onto the photo album.

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.

Copenhagen in 1937 — what can it tell us?

I thank Ralph Fertig of the Santa Barbara, California Bicycle Coalition for drawing the attention of the bicycling community to the following fascinating travelogue from Copenhagen, shot in Technicolor in 1937. Not all of the film is about bicycling, but the bicycling scenes are worth the wait.

Copenhagen TravelTalk 1937 from Justin Lim on Vimeo.

In 1937, bicycling had been the dominant mode of road transportation in Copenhagen for decades. No transition to motoring had occurred, as in the USA. Bicycling declined after WWII with the increasing popularity and affordability of motor vehicles, but has since recovered considerably with the construction of bicycle facilities and other measures to encourage bicycling, and extremely high taxes on new cars.

The film from 1937 shows some very interesting scenes of bicyclists interacting with the relatively few motorists, especially near the end. Interaction is mostly vehicular, and bicyclists establish the prevailing speed of traffic. Look at how they navigate a traffic circle, moving to the center to go straight through. Bicyclists conduct themselves much like motor scooter users I saw in Taiwan in 2002.

I also notice that the youngest bicyclists shown are in the early- to mid-teen years. That also comports with what I saw in Taiwan, and differs from the “eight to eighty” paradigm that must be accommodated only with separate facilities, or on streets where motorists operate very gingerly — eight-year-olds can’t reliably follow the rules of the road.

Clearly, pre-WWII Danes were experienced bicyclists, but on the other hand, there is some rather sloppy bicycling shown.

Gotta love the narration:

“…a people who have contributed to the stability and progress of the white race, for the Danes are the descendants of the courageous Vikings…”

I had mistyped Bikings :-)

Those Vikings were rather ruthless expansionist warriors, actually (just ask the Scots) , and in 1937, the Danes were within a very few years of being invaded themselves by history’s most brutal exponents of the concept of the “white race.”

New York City bicycling advocate Steve Faust adds the following observations:

I think I recognize the bridge…just west of the center city,
if so, the roadway has been changed from 4 mixed roadway lanes with trolley tracks in the center,
to two motor lanes without any streetcars, and two cycle track lanes – one on each side for one way bicycle flow.
The pedestrian sidewalk space remains about the same width as in the film.

The streets leading to and from the bridge have been given a cycle track treatment in place of the two motor lanes [sic], and probably are part of the bicycle speed paced green wave of traffic signals.

There is almost as much bike traffic on these streets today, plus more motor traffic volume, all on the same street width.
The major change besides the dedicated cycle tracks, is the use of the right hand left turn in a holding bike box on the far side of the intersection. This eliminates bikes having to merge across the car lane and possibly more critical, bikes don’t wait in the motor lane for a clear left turn, which waiting would block the relatively narrow motor lane – there are no left turn pockets.

Cyclist waiting time is minimized by having a total 60 second traffic signal cycle time. A cyclist arriving on the green through light has less than 30 seconds to wait at the far corner for the cross street green light – a delay that might well be shorter than waiting for a clear left turn from the roadway. I’ve certainly stood for over 30 seconds in the middle of the road waiting for a safe clear left turn.

The bike box Steve is discussing is a cross-street bike box, which serves only left-turning traffic.

The graph below is from a presentation by Dutch bicycle program official Hans Voerknecht given in Boston, Massachusetts, USA in November, 2008.

The mode share for Copenhagen is indicated by the green line that starts at around 40 percent in 1920, rises to around 55 percent either side of World War II, then falls and rises again to around 37 percent in 1995.

This widely quoted number, though, is for commute trips only.  According to more comprehensive sources from 1995 and also from more recent years — see this posting — bicycle trips are around 22% of all trips in Copenhagen. Data from earlier years and especially from before World War II may have been collected differently.

Copenhagen still has a large bicycle mode share for a city in an industrialized nation. Despite the draconian measures to reduce motor vehicle use, and the many bicycle facilities installed since the 1960s, Copenhagen streets carry many more motor vehicles now than in 1937, and on many main streets, bicyclists are restricted to cycle tracks or lanes which become congested at peak travel times.

You may click on the image to see a larger version.

Bicycle mode share in several European cities, 1920-1995

Bicycle mode share in several European cities, 1920-1995