Tag Archives: traffic signal

Is the NACTO Guide a Design Manual?

In cities around the USA, politicians, under pressure from populist bicycling advocates, have pointed to the NACTO (National Association of City Transportation Officials) Urban Street Design Guide and directed their engineering staff to install treatments which it describes.

I’ll say right here that some of the treatments which the NACTO guide describes deserve attention and inclusion in national design standards — though their presentation in the NACTO Guide typically is flawed, inconsistent and incomplete. Why some deserving treatments are not included in the national design standards is a story for another time.

Other NACTO treatments are so troublesome that they are not widely applicable.

Engineers unfamiliar with bicycling issues may take NACTO designs at face value; other engineers may throw up their hands and comply, faced with the threat of losing their employment. Several engineers who have extensive background and expertise in design for bicycling have resigned, been fired or been demoted when they would not accept the NACTO designs.

What leads to these problems? To put it simply, the NACTO guide isn’t a design manual. It is a smorgasbord of design treatments formatted — right down to digitally-generated loose-leaf binder holes on what are, after all, Web pages — to look like a design manual to politicians and the general public. Bicycle manufacturers funded it to promote street designs which they expect will lead to greater bicycle sales. It lacks the vetting necessary for consistency and accuracy. Its purpose is to generate political pressure to apply the treatments it describes. It is weak on specifics: rife with errors, and with omissions even in describing the treatments it covers.

If I described all of my specific  concerns with the NACTO Guide, I’d be writing a book, so for now let’s just look at a two-page spread of the NACTO Guide, the pages about two-stage turn queuing boxes (2STQBs, for short).

Maybe by now you are inclined to think of me  as a naysayer, so, let me get down to some specifics to dispel that impression. I have had information about two-stage turn queuing boxes online for years, I think that they are a useful treatment, and I use two-stage turns: when I realize that I have reached the street where I need to turn left, but hadn’t merged to turn; when traffic is heavy and fast and I haven’t found an opportunity to merge; when ordinary left turns are prohibited. My favorite example is the left turn from Commonwealth Avenue onto the Boston University Bridge in Boston, Massachusetts, where a no-left-turn sign is posted: motorists have to go around a large loop.

Ok, now let’s consider the spread from the NACTO guide, below.

NACTO pages about two-stage turn box

NACTO pages about two-stage turn queuing box

I have placed that spread online as a PDF file, zoomable to any size you might like. You may click on the link or the image above to get a larger view while reading this text. The PDF will open in a separate browser window or tab. I’ve also posted parts of the NACTO pages in connection with the text below.

Issues of organization and use of technical language

The NACTO treatment of the two-stage turn queuing box presents issues of organization and of use of technical language.

Problems start with the title of the section. A proper title is not “Design Guidance”, otherwise, every section would be named “Design Guidance”. A proper title is the name of the device, here “Two-Stage Turn Queuing Box”. [And not “Queue” but” Queuing.”]

In a proper design manual, the terms “shall”, “should”, “guidance” and “option” go from strong to weak. “Shall” is imperative: for example, a stop sign shall be octagonal. Should, guidance and option statements are increasingly weaker, leaving more room for engineering judgment.

The terms “Required Features” and “Recommended Features” correspond roughly to “shall and “should” but do not have the explicit, legally-defined meanings of “shall” and “should”.

None of the drawings on the two pages are dimensioned, and no dimensions are given in the text. That is to say, these are not engineering drawings, they are only conceptual drawings. How big are the turn boxes supposed to be? Who knows? The width of travel lanes differs from one drawing to the next, but no explanation is given for that. When politicians start beating on the door for NACTO treatments, standards-setting bodies and traffic engineers have to try to fill in the missing information. For specific projects, that task often is passed along to hired consultants who make their living by promoting and designing special bicycle facilities. Yes, there is a conflict of interest.

Specific comments

Now, either click on the image of each section of the page below to open it in a separate browser tab, or zoom the PDF to at least 50% size so you can read the text in connection with my specific comments .(You may open it now if you didn’t already.)

Comments on the left-hand page

The left-hand page includes text which may look like design specifications, and drawings which may look like design drawings — to a layperson.

Left half of left-hand page

twostageturn_guidanceLL

Point 1: “An area shall be designated to hold queuing bicyclists and formalize two-stage turn maneuvers.” This is under the heading “Required Features.”  A 2STQB is only one way to turn left among others, an option, subject to engineering judgment or specific design warrants. There is neither the room nor the need for a 2STQB at most intersections. Lacking here is any statement as to where a 2STQB is appropriate, but the “shall” statement here is inappropriate: appropriate shall statements would describe what features are required if a 2STQB is installed. As of May 2014, the 2STQB is still in experimental status with the Federal Highway Administration — as are all details of its design, and so no “shall” statement at all is appropriate.

A proper design manual would include guidance about speed and volume of traffic; the additional delay usually required for a two-stage turn; whether bicyclists might take an alternate route entirely; whether use of the box is  mandatory, placing bicyclists who make other types of turns in violation of the law.

Point 4: “In cities that permit right turns on red, a no-turn-on-red sign shall be installed.”

According to the wording here, if the installation is not in a city, the sign is not required.

But also, the shall statement is overly broad, and incomplete. The sign is needed only if right-turning traffic would be in conflict with the bicyclists waiting in the 2STQB: unnecessary in the cross street if traffic turns right before reaching the box or cannot turn right, and unnecessary on the entry street if the cross street is one-way right-to-left. Does the sign belong on the entry street or the cross street, or both? That is not stated. Details, details…

Point 6: The comma makes nonsense of this sentence. Where is the box to be positioned?

The other, subsidiary “should” and “may” statements on this page also are contingent on official approval of the underlying design, and are lacking in detail.

Right half of left-hand page

twostageturn_guidanceLR

Something really leaps out at me here: take a look and see whether it leaps out at you too.

OK, ready? Three of the six illustrations show a line of travel (in blue) for bicyclists straight across an intersection and then illegally and hazardously turning right, directly into the face of approaching traffic in a cross street.

In showing this bizarre routing, the NACTO Guide also fails to address issues with the actual route which bicyclists might take.

Five of the six illustrations show that bicyclists would somehow turn 180 degrees in place. That requires dismounting and is slow and awkward. How would a bicyclist turn when the traffic light is about to change? When other bicyclists are already in the box? What about tandems? Bicycles pulling trailers? Bicycles carrying heavy baggage?

The drawings show a subtly implied but selectively addressed-threat: lanes where motorists travel are shown in a threatening shade of pink — whoops: except in the cross street where bicyclists ride head-on at motorists.

Four of the six illustrations show motor vehicles in right-hook conflict with bicyclists headed for the queuing box. The motor vehicles are turning out of the threatening pink area into what is portrayed as the safe zone– the right-hook zone. In two of the pictures,  vehicles have already impinged on the blue line which represents the path of bicyclists crossing the intersection. Green paint, which has become a catch-all warning of traffic conflicts in bicycle facilities, is shown in the queuing box, it is not shown in the conflict zone. (By way of comparison, Dutch practice in such conflict situations is that the motorist must always yield, and to use “shark teeth” markings to indicate a yield line.)

Two of the drawings show bike lanes in the door zone of parked cars.

The middle left illustration shows a receiving bike lane at the top, out of line with dashed markings in the intersection, so bicyclists bear right just before they cross a crosswalk, potentially colliding with pedestrians who would expect them to continue straight.

All of the illustrations show two-stage turns across two-lane one-way streets, though the two-stage turn queuing box is most useful where a conventional left turn is illegal, unusually difficult or hazardous — for example, when turning from a major, wide arterial street with heavy traffic, or one with trolley tracks in the median.

As already indicated, none of the drawings are dimensioned and no dimensions are given in the text.

Comments on the right-hand page

The right-hand page gives annotated pictures of conceptual installations, with angled views from overhead.

Left half of right-hand page

twostageturn_guidanceRL

The street going from bottom to top in the picture is one-way, as can be inferred by the direction in which vehicles are traveling. That the cross street is two-way may be inferred from the locations of traffic signals and the existence of the queuing box. A real design manual would be explicit about how a treatment would apply, depending on the directions of traffic in the streets.

The end of the traffic island next to the queuing box protrudes so far and is so sharply as to make right turns awkward. No explanation or guidance is given on this issue.

Traffic signals are shown for motor traffic on both streets, but no traffic signal is shown facing the separate bikeway in the street!

Point 3: “Shall” — mandatory — wording differs from that in the same point as made on the opposite page. A real design manual would have a single, consistent statement. “Queue box shall be placed in a protected area.” The queuing box shown here is not protected from right-turning traffic in the cross street. How would that right-turning traffic be managed, or is it permitted at all? Such issues are addressed in a real design manual.

Point 6: “Optional queue box location in line with cross traffic.” The preferred queuing box, then, is not in line with cross traffic. On getting a green light, bicyclists in the queuing box would have to merge left inside the intersection unless there is a receiving bike lane after the intersection, but none is shown. Merging inside an intersection results in hazardous conflicts and is generally illegal. What warrants the choice of one or the other option? It isn’t stated.

Point 8: The illustration shows motorists and a bicyclist inside the intersection, and so they must have a concurrent green light — or, they would if any signal were shown facing the bikeway. Markings guide bicyclists across the intersection, but also into the path of right-turning traffic. The bicyclist and the motorist in the right-hand lane at the bottom of the picture are on a collision course if the motorist turns right.

What is the meaning of the curved markings adjacent to the bicycle parking in the middle of the street? Does the lane with bicycle parking start as a lane with car parking, additionally hiding bicyclists from turning motorists? Or is this an additional lane for motor traffic, discontinued at the intersection, precisely where more lanes are needed to store waiting traffic? Not shown.

Right half of right-hand page

twostageturn_guidanceRR

There is a right-hook threat at both bike lane entries to the intersection.

Bicyclists headed from bottom to top in the bike lane are riding in the door zone of parked cars, and closer to the cars after crossing the intersection.

Point 9: As in the left half of the page, placing the queuing box to the right of the travel lane when there is no receiving lane ahead assures that motorists will overtake bicyclists in the intersection and that bicyclists will have to wait for motor traffic to clear before they can proceed. Motorists waiting to turn right will be stuck behind the bicyclists. Placement out of line with motor traffic is described as the option here, rather than as the preferred treatment as on the left side of the page, and the problem is acknowledged in the caption to this drawing, though no explanation for the different choices is given.

Point 10: A jughandle may be useful if traffic is so heavy or fast that bicyclists have difficulty merging to the normal left-turn position near the center of the street, but then traffic is also so heavy and fast that a signal is usually necessary, not merely to be considered — unless there is already one upstream.

Point 11: Yes, signage may be used, but what signage? A real design manual would show the signs and where they are to be placed.

Point 12: A bicycle signal might be installed, but where? for the entry? For the exit? Its timing?

Point 13: Guide lines, pavement symbols and/or colored pavement. Which? Where? Why?

Had enough?

Danish story, video and comments on the Albertslund-Copenhagen “bicycle superhighway”

A reader pointed me to a news story on the politiken.dk blog about the Copenhagen/Albertslund “bicycle superhighway” which is getting attention and publicity. The reader’s comments on my previous post read:

Yeah, its kind of joke, but to be fair they are not called superhighways in Danish but Super bicycle tracks, and even then most agree that they are not really that super. There is a video of the entire route here if you scroll down a bit:

http://politiken.dk/debat/skrivdebat/ECE1615543/er-koebenhavns-nye-cykelsti-virkeligsuper/

The two next ones which will open are another story though, as they mostly have their own right of way, and use viaducts or bridges to cross streets.

So, better things may be on their way, but…I ran the article through the Google translator, and it appears in the link below in (sort of) English. The page includes the sped-up video of the entire route.

http://translate.google.com/translate?sl=auto&tl=en&js=n&prev=_t&hl=en&ie=UTF-8&layout=2&eotf=1&u=http%3A%2F%2Fpolitiken.dk%2Fdebat%2Fskrivdebat%2FECE1615543%2Fer-koebenhavns-nye-cykelsti-virkelig-super%2F&act=url

Here’s the video — warning, Shell diesel fuel ad at start, and you can only stop the video when you click on it, see the ad again and click on it to open a bigger ad! This workaround was needed to make the video visible on this page.

The one unifying factor of this route is an orange line painted lengthwise to identify it. The first part of the route is relatively tame. Barriers, unprotected intersections and other hazards pile up near the end.

Some representative quotes (I’ve translated from Googlish to English, thanks to an online dictionary and my knowledge of the neighbor language, German.):

From the article:

“I did not expect that I just had to detour on ordinary roads in residential neighborhoods. I did not see much of the green wave that is supposed to be in town. I do not think you can call it a super bike path,” the [politiken dk test rider] concluded.

From comments on the article:

- The section of tunnel under Motorring 3 is dark and miserably lighted. There are many riding schools (which, incidentally, should be forced to close and move out into a rural area!). The tunnel is usually filled with horse s***, and because you can not see in these tunnels due to poor lighting, you can only hope that you do not ride through any of it.

*****

- In the westbound direction, at the pitch-dark tunnels, you have to negotiate two sets of barriers. The point of these, other than to impede traffic, I do not know. But when you have to use all your mental energy to get through these, they constitute more of a hazard than a safety precaution.

*****

I have commuted between Roskilde and the northwest part of Copenhagen 2-3 times a week on a recumbent trike with an electric assist motor for 6 months (http://ing.dk/blogs/pedalbilen). When I used the “super path” the trip was about 3 km and 15 minutes longer. Especially the part of the route in Albertslund is very indirect and inconvenient. There are detours, barriers and ramps in most places, and it will for example not be possible to ride in a velomobile, as far as I can judge. The new route is comfortable and free of exhaust, but as commuter route it gets a failing grade compared with Roskildevej [a parallel, 4-lane divided but not limited-access highway with one-way sidepaths].

*****

- I didn’t see anything which shows that cyclists have priority over the other traffic. Unfortunately, the only thing new that I see is approximately 100 meters of new asphalt in two places near Rødovre, so that it is easy going. There are simply no real improvements for cyclists in relation to other road users! You can still find barriers, sharp turns, bumps and traffic lights. Why is there no new cycle path, e.g. along the western forest road, so you do not have to drive through neighborhoods with pedestrians and children playing? Why are barriers not turned 90 degrees, so users of the route have right of way?

Even if there were brand new asphalt on the entire route it would never merit the title “super”. Only when a route enables more or less continuous travel at high average speed (which motorists know from motorways) does it, in my opinion, deserve the massive marketing it is currently getting.

*****

…Bus passengers cross the bikeway. It seems quite unreasonable that there are no islands at bus stops where passengers have to wait when they get on and off. Thus cyclists must stop, and so, so much for the “super bike path”.

A ride on Comm Ave., Boston, Massachusetts, USA

Comm Ave. Boston: Kenmore Square, Mass Ave. underpass from John Allen on Vimeo.

This is a 4-minute continuous video of a bicycle ride in Boston, eastbound on Commonwealth Avenue through Kenmore Square, to and through the underpass at Massachusetts Avenue. I recommend that you view it on Vimeo site, in full-screen high definition.

Gordon Renkes and I each had a camera, so you can see both a forward and rearward view. We rode safely, and mostly by not using the special bicycle facilities.

Some highlights:

  • The block pavers, bricks and the granite curbstones used as borders for crosswalks made for a very bumpy ride across Kenmore Square and the next intersection.
  • The bike lane for the first block after Kenmore Square was unusable, due to double-parked vehicles. In the next block, it was unsafe, due to the risk of opening car doors and walkouts. One trucker was accomodating enough to park entirely outside the bike lane, inviting bicyclists to run the gauntlet between the truck and parked cars Gridlock Sam-style. We didn’t take the invitation.
  • As we waited for a traffic light, a cyclist raced past us on the right, entering the narrow channel between a row of stopped motor vehicles and one of parked cars. If anyone had walked out, or a car door had opened, the cyclist would likely have had too little time to react, and he would have had no escape route. At least he (and the pedestrian he could have struck) would have been fortunate in that one of the waiting vehicles was an ambulance.
  • There is a bike box along the route, and revealed an issue that I hadn’t noticed before. If the traffic light is red, you’re supposed to filter forward in the bike lane on the right, then swerve across two lanes of traffic to the middle of the 4-lane wide bike box, to be in line with the bike lane which is to the left of 2 lanes — see Google satellite view — note that this is an angle shot from the west. If the light is green, you could merge either before or after the intersection, but there is an advantage in merging before the intersection, as the counterexample of the video shows. You also don’t know when the light is going to change — so in either case, you make a widely divergent choice — merge left, or head for the bike lane at the right — based on insufficient information, and if the light is red, you also could be swerving abruptly across two lanes of traffic just as the light turns green.
  • The buffered bike lane in the underpass makes for an easier ride through the underpass, but where it connects to a narrow left-side bike lane outside the underpass, there is little clearance for motor traffic in the next lane, which is the faster of two travel lanes. There also is a risk of left-hook collisions. I used to ride in the right lane, claiming the lane, and that was simpler and less stressful.

More general comments:

  • The block pavers, bricks and curbstones buried in the street are not bicycle-specific, but certainly not bicycle-friendly. I predict that they will be paved over within a few years as they deteriorate.
  • The attempt to engineer a “bicycle friendly” or “low-stress” solution on busy, crowded Commonwealth Avenue is like ornamenting a pig with lipstick, costume jewelry and a party dress. The bicycle-specific measures, except the bike lane in the underpass, fly in the face of the way traffic works, and the way it uses this street. Experienced, competent cyclists like Gordon and me know how to avoid the hazards, but they worsen our experience anyway — it is in Kenmore Square (during another ride) that I first heard the call “get in the bike lane” in Boston. Less knowledgeable bicyclists garner a false sense of security, following the painted lines, and expose themselves unnecessarily to risk.
  • Meanwhile, other, better solutions beckon. I have long advocated that Boston designate and improve alternative routes on lightly-traveled streets for through bicycle travel. That would be especially easy in Back Bay, with its grid layout. My candidate for an alternative to Commonwealth Avenue would be Newbury Street, the next one to the south, a shopping street which could make a very nice bicycle boulevard, and which, with a little bridge across the Muddy River, would also connect under the Bowker Overpass into the Fenway area. A worse solution also has been proposed: the City is considering a so-called “cycle track” — a bikeway behind a row of parked cars — on the next Street after Newbury Street, Boylston Street. More about these topics later…

Bikes, Cars, Light Rail, E. Jefferson St., Phoenix, Arizona

Build it and they will…wait. Well, at least they’re supposed to wait.

If you click on the title in the image or caption, you can view this at a higher resolution.

Bikes, Cars, Light Rail, E. Jefferson St., Phoenix, Arizona from John Allen on Vimeo.

An intersection with light rail, motor vehicles and bike lanes requires bicyclists to cross from one side to the other of a multi-lane street, resulting in delays of 2 to 3 minutes. Alternative solutions are described.

The Six-Way in Rush Hour

Here’s another video showing conditions at the six-way intersection of 16th Street, U Street and New Hampshire Avenue NW in Washington, DC, where special bicycle facilities have been installed.

Also please see my earlier post about this intersection, with another embedded video.

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.

My September 11

My 10-year-old son Jacob’s school year hadn’t started yet on that brilliant clear September morning. My wife had left for work. I  had a business appointment in Belmont, a few miles from our home. Jacob and I set out for Belmont around 9 AM on our tandem bicycle. There wouldn’t be much traffic; the morning rush hour had passed. I had 30 years of safe cycling in Boston-area traffic, and little concern about our completing the trip safely.

Through an open car window I heard a word or two…Boeing 757 airliner…I got a spooky feeling. No radios were playing music or the boom chicka chicka booom chicka rant (expletive) rant rant rant which passes as music. I’d gladly have had that instead, thank you.

Jacob and I were turning left from where the car is in the picture. Note the hedge on the far left corner.

Jacob and I were turning left from where the white car is in the picture. Note the hedge on the far left corner.

Jacob and I were waiting just to the right of the double yellow line at a red light, to turn left from Waverley Street onto Thomas Street, near Belmont Center. Both streets are relatively narrow two-lane, two-way streets with light traffic. My left arm was extended in a very clear left turn signal. The traffic light turned green, and just as I began to swing the tandem to the left, I heard “beep beep” of a car horn behind us. A small gray sedan going about 30 mph passed us on the left side of the street, an insanely hazardous maneuver not only because of the possible collision with us, but also because someone might be making a right turn on red from Thomas Street, and would of course be looking the other way for traffic. A hedge blocked the view around the corner, too.

…two classic bicycle-on-wrong-side-of-the-street crash types, only with roles switched around…

Jacob and I rode the couple of hundred yards to the Belmont police station and spoke with Officer MacEachern, who was very supportive and professional. I didn’t get a look at the driver, but Jacob did, and identified her as a woman with brown or black hair (dyed?) and, he thought, wearing glasses. We reported the license number of the car, 350 JBA. The officer verified that it was for a gray Toyota Corolla sedan, and told us that it belonged to a 75 year old woman who lived in Belmont.

Officer MacEachern said that his department unfortunately could not issue a citation, since an officer had not seen the incident, but that he would go have a talk with the driver and that it might be possible to pull her license if she is incompetent.

I can understand being termporarily out of one’s mind. One time I was injured but felt no pain, even ignored the grating of bone on bone, just had to get — home. Once a truck strayed into my lane and sideswiped my car. Only my quick swerve avoided a head-on crash. I was going to turn around and chase after the truck except that my wife calmed me down.

Maybe the driver was the daughter of the car’s owner, who was in turmoil…maybe she had children at home and hoped to spend her final minutes with them.

Maybe she had someone on one of those planes — two flew from Boston — or in one of those buildings.

Jacob and I rode on to the home of my client where I shot the photo below.

Televison news coverage of the September 11 attack on the Pentagon.

Television news coverage of the September 11 attack on the Pentagon.

And that is how my son and I might have been killed on September 11 2001, not by Al Queda fanatics in red-hot hatred, though very likely through a ripple effect of their apocalyptic, ruinous madness onto someone I would probably have been happy to have as my next-door neighbor.

I went back a few weeks later and took the picture of the intersection, so I could include it in what is mercifully the story of a non-event and gets news coverage only here. Even if Jacob and I had been killed or gone to the hospital, our crash would have gotten even less attention than bicycle crashes usually do, on that day.

A take-away? Every  variety of opinion about Al Qaeda has probably already been expressed so I’ll only say this: adrenalin is a powerful mind-altering drug. It is available only by prescription except when you make it yourself, and because you do, police can’t cite you for it after a crash. But still, please think twice…

The Six-Way, Washington, DC, a Second Look

The video embedded below documents a bicycle ride by the author and two companions in Washington, DC where special bicycle signals and road markings have been installed to establish continuity of New Hampshire Avenue at its intersection with U Street and 16th Street.

The video tells the story of an unusual pass through the intersection — the signal actuator somehow didn’t give us the green on the first go-round. It did on other passes.

Aside from that one quirk, the video shows the usual signal timing (though it might be different at another time of day). The most significant finding is the short time to get into the “bike box” which is located ahead of motorists’ advanced stop line. There wouldn’t be be enough time for any large number of bicyclists who had been waiting for the signal.

Several additional issues remain to be shown in other videos. Here is a preview of what they will show:

  • The bike boxes are very small, also a problem with large numbers of bicyclists.
  • Motorist encroachment into the bike boxes is endemic.
  • Some motorists misunderstand the installation to the degree that they become angry at bicyclists who use it as intended. We were buzzed on one pass by someone driving a big black SUV.
  • Probably 90 percent of cyclists passing through this intersection on New Hampshire Avenue do not use the facility as intended. Rather, most use the crosswalks — commonly going around clockwise. With the option to go either clockwise or counterclockwise, bicyclists can start across on either pedestrian phase, rather than having to wait through as much as an entire signal cycle for the special bicycle phase.

Before I actually rode through this installation, I thought that it was a particularly good one. I have a blog post expressing that opinion. That post also gives a detailed description of the installation and its history.

The installation doesn’t violate any principles of traffic theory. In particular, when used as intended, it doesn’t place bicyclists and motorists out of sight of each other and on a collision course. But as Yogi Berra, or maybe Albert Einstein, memorably said, “[I]n theory, theory and practice are the same. In practice, they are not.” This installation makes the intended movements unattractive due to the short timing and tight space. The installation also makes bicyclists wait much longer to take the intended routes than to take others — which don’t even necessarily require illegal movements. As such, this installation unfortunately is not, in my opinion, successful.

Traffic theory: improving traffic signals to reduce pointless delay

A real-world time-space diagram, from Wikimedia commons.

A real-world time-space diagram

In theory, there’s no difference between theory and practice, but it practice, there is.

attributed to:
Yogi Berra
Jan L. A. van de Snepscheut
Albert Einstein

An optimal traffic-signal system would never present anyone with a red light or a don’t walk signal unless there actually is interfering traffic. In theory.

In practice, though, it may be desirable to introduce some delay in order to smooth the flow of traffic — to get vehicles on board a “green wave.” Traffic engineers think in sophisticated ways about this issue, but do not have the real-world tools to resolve it. While synchronized traffic-signal systems and sensor-actuated signals already improve the situation over uncoordinated timed signals, better sensing and more sophisticated software could, at least in theory, achieve much more.

Probably the most difficult part of the problem is in sensing approaching vehicles and pedestrians far enough ahead of an intersection so signals will change as they reach the intersection. Sensors are expensive, and many more would be needed. On the other hand, in a city dotted with security cameras, the sensor data may be easier to obtain, especially if traffic control is a goal when installing the equipment.

I am emphatically not describing so-called intelligent highway systems, intended to automate driving by taking control of vehicles. The driver then supposedly becomes a passenger, free to dial the cell phone, read the newspaper, watch TV or apply makeup without concern. For automated control to work, the system must exert at least as reliable control over vehicles as attentive drivers do. More yet: car makers have huge legal problems resulting from defects that injure only a small number of customers.

Automated control presently is applied only under very restricted conditions, on airport shuttle trains and the like. Even with a great increase in sophistication, it’s hard to conceive of how automated control (other than in collision-avoidance systems) would work on any roads except limited-access highways restricted to vehicles equipped for it.

Even under these conditions, there are difficult technical problems. Collision-avoidance systems to prevent collision with large objects ahead are just beginning to be common. Avoiding debris in the road, potholes and other smaller obstacles requires sophisticated sensing which a driver routinely performs — but well beyond the abilities of automated systems.

So, I am describing not a system to take over control of vehicles, but one to improve control of traffic signals. Humans would retain the ability to prevent collisions, and malfunctioning of the system would lead only to delay, not to crashes. The system would make little difference to anyone — motorist, bicyclist or pedestrian — except to reduce pointless delay.

Will this happen? If so, when and where? One promising thought is that it can happen bit by bit, at one intersection and another, rather than all at once along an entire highway.

Lyon study — cyclists ride faster in rush hour?

A blog posting published by the Massachusetts Institute of Technology describes a study of cycling in Lyon, France.

News accounts of the report are making some rather strange assertions, such as that cyclists ride faster during rush hour than in the middle of the day, and faster on Wednesdays. On the other hand, the Lyon study is very interesting in that it aggregates data on millions of bicycle trips, recorded in the database of Lyon’s card-swipe bicycle-rental system.

I see two problems with this study, and more so with news items about it: not all data were collected that would be needed to describe cyclists’ trips accurately; also, there is a rush to conclusions, without looking at some rather important characteristics of cyclists’ trips.

Certainly, cycling can achieve shorter trip times than motoring when motor traffic is congested, whether by cyclists’ filtering forward on the same street or by choosing other streets, paths, riding against traffic, whatever. What I can’t grasp is how any individual cyclist would achieve a shorter travel time in rush hour than at other times.

Congested motor traffic slows bicyclists, though not as much as it slows motorists — because cyclists have a lower speed capability in the first place, and because cyclists have a greater choice of routes, and can filter forward. Even with bike lanes (of which, according to the article, Lyon doesn’t have any), congested motor traffic slows bicyclists. But also, congested bicycle traffic and pedestrian traffic slow bicyclists.

The Lyon data include only the times and locations of rental and return of the bicycles, and odometer readings. The data, then, cannot show where bicyclists went, and can record only an average speed. Importantly, the slower mid-day times may reflect rentals during which the bicycle is parked in mid-trip — shopping trips, or trips to appointments, lunch dates, classes, (Lyon is a major university city). Women’s speed capability is generally only slightly lower than men’s; to claim it as an important explanation is at least vaguely offensive. Morning and evening bicycle commuters, whether male or female, might be regular bicycle users, in better physical condition, more skillful in traffic and so capable of higher speeds. Without demographic data, there’s no way to know.

The report does include some interesting results about the shortest travel times, which it is safe to assume do not involve parking in mid-trip.

Bicycles included in the study are available at rental stations spaced around Lyon. A renter may obtain a bicycle at one station and leave it at another, making the system practical for single-direction trips. But renters must walk to the stations — the bicycles are, for example, not at their homes. Bicycles will not be used for the shortest trips unless stations happen to be very convenient to trip origins and destinations. Also, the system works only within the limited area where stations exist. These factors can be expected to affect the trip lengths recorded in the study.

I look forward with eager anticipation to a study using GPS data correlated with user data, so it is possible to categorize the cyclists, determine where they went, how fast they actually rode, and whether they parked the bicycle in mid-trip.