Category Archives: New York City

Scaling up and scaling down

New York bicycling advocate Steve Faust has stated that some ways of accommodating bicycling do not “scale up” — that is, they work with small numbers of cyclists, but less well with larger numbers.

His central complaint is that use of roadways with no special bicycle facilities, according to the conventional rules of the road, does not scale up well.

I might put that a bit differently. After all, more cyclists need more room. Mass rides such as New York’s own 5-Borough Tour avoid special bicycle facilities and occupy the entire width of Manhattan’s multi-lane avenues. Motor vehicles are excluded while these rides pass through. Interaction within the group of many thousands of cyclists is for the most part according to the conventional rules of the road, and falls short only in that many of the participants are inexperienced.

On roadways carrying both cyclists and motorists, cyclists inconvenience motorists when the motor traffic could go faster — that is, when there are many cyclists and few enough motorists that they could travel unimpeded, if not for the cyclists. Motorists inconvenience cyclists when motor traffic is congested, and stopped or traveling slower than cyclists might want to go. Level of service always declines as a road becomes more congested, and it declines faster when vehicles have differing speed capabilities.

On the other hand, there also are situations in which operation as intended does not scale down to smaller numbers.

Motorists are more likely, for example, to yield to a crowd of pedestrians than to a single pedestrian.

Another example is the leading pedestrian interval: the walk signal goes on a couple of seconds before motorists get the green light. The leading pedestrian interval is intended to get pedestrians moving out into the intersection before motor traffic can begin to turn across a crosswalk, encouraging motorists to yield to the pedestrians. The same approach is used sometimes on bicycle facilities, for example on the Boulevard de Maisonneuve bicycle sidepath in Montréal, Québec, Canada. But a leading interval only works if there is someone waiting to cross when the signal changes. With smaller numbers, so the first pedestrian or bicyclist reaches the crossing after the motorists get their green light, the leading interval’s only achievement is slightly to reduce the capacity of the intersection.

The same issue can occur with any “conflict zone” with poor visibility as users approach, including the “bike box” or bicycle waiting area ahead of the stop line for motorists at an intersection. Once one cyclist is in a “bike box”, a motorist is unlikely to move forward, because that would require running over the cyclist. Therefore, the bike box is then safe for the entry of other cyclists, at least into the same lane in which the first cyclist is waiting.

The”bike box” works as intended when there are large numbers of cyclists so the first one arrives well before the traffic signal turns green.

If there are few cyclists, so the first one is likely to arrive just as the traffic signal turns green, then there is the potential for a right-hook collision, or a motorist’s colliding with a cyclist swerving into the bike box.

Safety requires that there be enough cyclists that early-arriving ones block the way of motorists, or at least alert the motorists that others may arrive. This safety factor does not scale down to small numbers.

Research in Portland, Oregon shows that only 5% of bicyclists swerve into the bike box when they are first to arrive; about 35% if they arrive later. The reluctance of the first-arriving cyclist reflects risk avoidance to some extent, due to not knowing when the traffic signal will change, but also that the swerve lengthens the cyclist’s trip — none of the Portland bike boxes are designated for left turns. The later-arriving cyclists are to some degree protected by the arrival of the first one, but also they either have to wait behind or move over to the left of that cyclist, into the bike box.

“Safety in numbers” claims become rather interesting when such issues are considered.

The design challenge is to achieve efficiency and safety of all travelers, regardless of whether numbers are large or small.

Davis Planners and Advocates Opine on Sidepaths

This post supplements my previous post linking to documents about Davis bicycle facilities. Please bear in mind that Davis was the first community to introduce bike lanes in the USA, and that its bicycle program strongly favors conventional bike lanes, which are separated from the adjacent lane only by a painted stripe. However, I have found that the Davis documents uniformly and strongly recommend against bike lanes behind barriers or parked cars. Not only that, the recent warnings are more definite than the early ones. Some quotes, starting with the most recent and working backwards in time:

Theodore Buehler, Fifty years of bicycle policy in Davis, CA (Master’s thesis, 2007). See pages 50 ff., “Lane location relative to motorized traffic”.

The early experiments included three different types of bike facilities (see examples at the top of this section):

  1. bike lanes between car lanes and the parking lane (Third St.),
  2. bike lanes between the parking lane and the curb (Sycamore Lane), and
  3. bike paths adjacent to the street, between the curb and the sidewalk (Villanova Ave.).

The first bike lanes included all of these types, to test them in real life to see how effective they were. The on-road lanes worked best, the behind-parking lanes were the worst, and the adjacent paths were found to work in certain circumstances. This is an example of the wide level of experimentation that occurred during this period. Had the city tried to do extensive research without construction, it might have settled on an inferior design. And not having tried all three designs, it might not have recognized it as inferior, and the entire experiment could have been declared a failure.

Dale Lott (one of the early advocates for special bicycle facilities in Davis, who also conducted research as to their safety and effectiveness), “How Our Bike Lanes Were Born“, op-ed piece which appeared in the Davis Enterprise in 2003:

We insisted on some experiments that turned out well and some that were flops.

One flop was on the first block of Sycamore north of Fifth where we put bike lanes next to the curb with parking next to the auto travel lane. It looked great on paper, but was a mess on pavement. When cars turned into the University Mall driveway, they crossed the bike lane. Both driver and rider, whose view of each other had been obscured by the parked cars, had an emergency situation.

David Takemoto-Weerts (University of California, Davis Bicycle Coordinator, A Bicycle-Friendly Community, the Davis Model (conference presentation, 1998)

Because Davis pioneered the bike lane and other bicycle facilities in this country, it is not surprising that some “experiments” were less successful than others. One such example was the construction of “protected” bike lanes where motor vehicle and bicycle traffic was separated by a raised “buffer” or curbing. In some cases, the bike lane was established between the parking shoulder and the curb line (i.e. cars were parked on the left of the bike traffic lane). Needless to say, any “benefits” of such facilities were soon found to be outweighed by the many hazards created for their users.

Most such well-intentioned, but ill-fated designs were phased out long ago. However, some facility design decisions made decades ago were not so easy to remedy. The most pervasive example in Davis is the two-way bike path immediately adjacent to a roadway. Particularly problematic are single two-way paths located on only one side of the adjacent road. The problems associated with these designs have been described in any number of publications, and they are well illustrated at several locations in Davis. In spite of this documentation, some residents, city officials, and developers remain quite vocal in advocating such facilities when new construction is being planned and designed. The city and campus have attempted a variety of mitigation strategies to reduce the hazards or inefficiencies associated with these side paths, but many observers believe that continuing to build such facilities is wasteful at best.

Deleuw, Cather and Company.: Davis Bicycle Circulation and Safety Study. 1972 (excerpt — for complete document in three parts, see table of contents page.

Protected lanes

…Protected lanes located between the parking shoulder and curb line have most positive separation. However, the parked cars create sight distance problems at driveways and intersections. Inability to cross streets in midblock in this type of treatment results in two-way usege which, in turn, leads to intersection problems described subsequently…

Sidewalk and Independent paths

Sidewalk pathways eliminate midblock bike-motor vehicle friction. However, frictional interference of pedestrians may discourage usage of these facilities as does frequent interruption by cross streets and driveways or meandering of the path. An additional problem is establishment of a visual relationship between motor vehicles on the sidewalk path on approaches to intersections…

Green Wave, Checkered Flag?

A green wave moves out, Manhattan, 1986.

I am writing this post in response to comments by Mighk Wilson and Khalil Spencer on another post on this blog. They discussed the difficulty of cycling in a city with synchronized traffic signals (a “green wave”) set to a higher speed than cyclists can manage, and the potential of a slower green wave to make a street more attractive for cycling. I’d like to take a more general  look at the green wave and how it affects traffic.

My understanding of the green wave is based mostly on experience. (And so, anyone who can provide more details based on theory, or can correct me, please do…)

In my high-school years, I lived and learned to drive in Baltimore, Maryland, USA, one of the first cities to implement traffic signal synchronization. I have also lived, driven and cycled in Manhattan, where most traffic lights are timed to create green waves.

A green wave can only work under a limited set of conditions. If these do not apply, then despite best efforts to time traffic lights for the smoothest possible traffic flow, a signal sequence can still appear random. Drivers have no clear strategy for avoiding red lights beyond speeding up when the next light is still green. On the other hand, when a green wave is working smoothly, drivers may feel as if a green-wave Tinkerbelle is darting along overhead and pointing her magic wand at every traffic light to turn it green.

Traffic engineers use clever math so a green wave, surprisingly, can be applied to streets heading in more than one direction the same time — though it words better if they are one-way. Heading north on Charles Street from church in downtown Baltimore, my family would get  green lights for block after block, except at the few two-way streets, where all bets were off. Then as we headed into the more random street pattern at the north end of the city, we just had to take each traffic light as it was. On the other hand, traffic lights were less frequent in this less densely built-up area.

My experience was similar in Manhattan. The green wave worked smoothly on one-way streets and avenues, but  when crossing two-way ones, and when driving on them, it didn’t. This obvious difference gives drivers a strong incentive to use one-way streets and avenues for through travel, where possible. Advocates of the sort who would view streets as a neighborhood resource often protest conversions of two-way streets to one-way, see for example this call to action. Traffic engineers who are concerned with the effect on congestion and crash rates have the opposite opinion — see, for example, this presentation. (I expect that the choice is not quite so stark as these two examples make it — as usual, such decisions must be made on a case-by-case basis.)

A green wave works smoothly only when there are no stop signs on a green wave street, though stop signs can be used on cross streets.  Double-parked vehicles, vehicles that have entered the street and are waiting for a light to change, vehicles — including bicycles — that can’t keep up with the pace set by the signals — anything that slows traffic down or reduces the number of lanes available increases the likelihood of not keeping up with the pase set by the lights.

A green wave often encourages travel faster than the pace set by the signals. That’s because there is an advantage in racing to the front of a platoon — where each signal has just changed to green — when preparing a turn — then after turning, racing to the end of the block so as to catch the end of the green there. A driver may speed through another few blocks to get to the front of the platoon before turning again. The advantage of this tactic is quickly obvious: After turning the corner at the head of a green wave onto another green wave street, a driver will be facing a signal at the next intersection which is about to turn yellow, then red.

The typical 30-mile per hour speed limit in grid cities like Manhattan often leads to motorists’ speeds considerably in excess of that limit, and to more unpleasant conditions for bicyclists.

On the other hand, synchronizing signals to a speed more comfortable for bicycling will discourage use of a street for through motor-vehicle travel, making it more attractive for bicycling. I have ridden on a street in Saint Petersburg, Florida, with the signals synchronized to 15 miles per hour, and it achieved that goal quite well. It would have worked better if it had been one-way — it ran up a moderate slope from the waterfront, and for most bicyclists, 15 miles per hour was hard to maintain. Downhill, on the other hand, the speed setting could have been 20 miles per hour without creating difficulties for bicyclists.

Bear in mind, though, that comfortable level-ground travel speeds for bicyclists cover a 3 to 1 range , from about 25 miles per hour down to 8 miles per hour — not nearly as uniform as for motorists, even considering the issues with motorists’ speed already mentioned. A predictable increase in the volume of electrically-assisted bicycles and motor scooters will complicate the issue of speed setting even further. The advantage of a slow green wave, given these issues, is not so much to allow bicyclists to travel farther before facing a red light as to discourage use of the street for through travel by motorists.

Guest posting by John Schubert: New York, City of Confrontation

Responding to an article in the New York Times, a correspondent asked John Schubert

Why isn’t NYC concerned about being sued because of lousy bike-lane-
design-caused wrecks?

and he replied:

Good question. I think it’s important to know the answer from NYC’s point of view. I’m not their spokesman, but I’ll try.

First of all, they get sued no matter what they do. It’s a city of confrontation.

Second, NYC knows it will always have collisions, injuries and deaths. They would not view any one street design as a perfect protection against these problems, nor against litigation.

Third, they are SO bombarded with aggressive drivers, nonmotorized road users wanting some sort of relief from aggressive drivers, and the usual paint and path propaganda, that they buy into the idea that separation is necessary in NYC, even if not elsewhere, because NYC is unique.

I believe NYC does have a civility problem. Separated bicycle facilities don’t solve that problem, but in the minds of true believers, at least they avoid that problem. I think you can’t have a livable community without addressing THAT problem.

NYC does have other unique concerns. I suspect the biggest is the huge volume of midblock car stops, more than anywhere else, mostly because of taxis getting and discharging passengers. I think the designs they use to answer this are silly, but the ‘vehicular cyclist’ alternative hasn’t been made appealing to them. Yet.

Ciccarelli on cycle tracks

John Ciccarelli is a consultant on bicycling and a League of American Bicyclists-certified cycling instructor who specializes in teaching adults who have never ridden a bicycle before. His comments here are reprinted by permission, and are in response to an e-mail he cites.

Subject: Re: Making Cycling Irresistible: Lessons from the Netherlands, Denmark, and Germany
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Gridlock Sam’s magic powers!

New York’s former Traffic Commissioner and Chief Traffic Engineer, Sam Schwartz, “Gridlock Sam,” who describes himself as a “traffic guru”, has posted a Web page [updated and expanded since my original posting] instructing bicyclists and truckers in how to interact. Truckers are supposed to double-park outside a bike lane, and bicyclists are supposed to ride in the channel between the curb or curb parking and the double-parked trucks.

[Update to post, November 2011: Sam misinterprets the New York ordinance prohibiting double parking in bike lanes as also requiring bicyclists to stay in the bike lane. As this is unsafe, and in some cases impossible, it is not required even under New York City's restrictive mandatory bike lane ordinance. City ordinances, at least as Sam interprets them, do permit truckers making deliveries to park outside the bike lane, reflecting the assumption that cyclists will run the gauntlet between the parked truck and curb or parked cars. The same apparently applies to taxis discharging passengers.]

The following is an image from Sam’s page. I do not endorse what is shown! Please read on!


Look at that drawing again, carefully. You may click on it to see an enlarged version, if you like.

The bicyclists are giants, and the cars are tiny! The car in the middle, where it poses the worst problem for the bicyclists, is by far the smallest.
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Livable Streets proposal lacks credibility

I’m looking at a GOOD magazine/Streetsblog proposal for a “livable street”

This is a prime example of what I call the Photoshop school of traffic engineering. Anyone with computer graphics skills can generate a before-and-after comparison like this. Often, it looks very attractive to the untrained eye — but, whether the proposed changes make sense is another issue entirely.

It would be nice if the Streetsblog people who created this graphic had a few more clues about street design. Some of the issues:

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Technical and legal issues with the NYC 9th Avenue bikeway

All intersections along the NYC 9th Avenue bikeway are signalized, and it has separate bicycle signal phases at most of them. At the time of the field trip, December 5 and 6, 2008, some of the signals (especially at the north end) had not yet been installed or were not yet working, and so another visit to the site would be useful to view the complete installation.

Manhattan has typically in the past (since Henry Barnes set it up in the 1960s) had signals on the one-way avenues timed for 30 mph, except at two-way cross streets where that was not possible.

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Guest posting: John Ciccarelli on the NYC Broadway bikeway

[John Ciccarelli is a consultant on bicycling, League of American Bicyclists Cycling Instructor and member of the Bicycle Technical Committee of the National Committee on Uniform Traffic Control Devices. These comments are based on his observations during a field trip to examine bicycle facilities in New York City in December of 2008.]

Broadway bikeway, Manhattan

Broadway bikeway: clogged with pedestrians

For me, the pedestrian conflicts on a new unconventional Manhattan bikeway — on the pedestrian-enhanced blocks of Broadway starting south from Times Square — rendered that bikeway nearly useless — even though those blocks of Broadway are similar to the
9th Avenue layout in several ways:

  • Both streets are multi-lane one-way-southbound
  • Both have a left-curbside one-way bikeway
  • At intersections there is a bike signal and a left-turn pocket and turn-arrow for motor vehicles (where the cross street is two-way or one-way-left) Continue reading

Guest posting: John Ciccarelli on the NYC 9th Avenue bikeway

New York's 9th Avenue bikeway at 29th Street

New York's 9th Avenue Bikeway at 29th Street

Manhattan’s 9th Avenue bikeway, extending from 31st Street to 14th Street, is mostly a signalized left-curbside one-way on-street path, separated over most of its length from mixed-flow travel lanes by an in-street car parking lane. A couple of blocks near the end are separated only by a striped median or a single stripe. The barrier separation is the first of its kind in Manhattan but as is usual with bike lanes on Manhattan’s one-way avenues, the 9th Avenue bikeway on the left side — for two reasons:

a) Buses, which run frequently, use and stop in the rightmost lane of this multi-lane one-way street

b) Truck deliveries and taxi pickups/dropoffs occur in the rightmost lanes

Those activities are impractical on the left side of 9th Avenue on the bikeway blocks because the bikeway is separated from the rest of the Avenue by a left-side in-street parking lane. Continue reading