Tag Archives: crash

Monsere, Dill et al. — Not Yet a Review, But…

M. Kary, who prepared a review of the Lusk et al Montreal study, has had a preliminary look at the Monsere, Dill et al. study of barrier-separated on-street bikeways (“cycle tracks”) which the bicycle industry lobby PeopleforBikes is promoting as demonstrating their safety. Dr. Kary has given me permission to publish his comments here.

An Introduction To and Overview Of:
Monsere C, Dill J, et al. (2014) Lessons From The Green Lanes: Evaluating Protected Bike Lanes In The U.S. Final Report, NITC-RR-583

To begin with a platitude: traffic accidents are rare events. The totals are large only because the overall volumes of exposure are huge. Therefore, if considering safety in terms of outcomes rather than the underlying mechanisms of operation, any facility, no matter how poorly designed, will appear safe if examined over a short period of time.

But collecting data over a long period of time has its disadvantages too: not just cost and delay, but also the averaging, and therefore blurring, of the effects of various changing causes and circumstances. Nor does it work at all for facilities that are yet to be built. In response to these problems, engineers developed the methods of traffic conflict analysis. They can be seen as based on the following logical and kinematic necessities. First, in order for a collision to occur, the vehicles involved must eventually get on a collision course. Second, in order to get on a collision course, they must first get on a near-collision course. On the other hand, not all vehicles once on collision or near-collision course do end up colliding: their operators make course corrections and avoid that outcome. Such potentially dangerous but often ultimately safe trajectories, i.e. traffic conflicts, occur much more frequently than actual collisions, deaths, or injuries. If there exists a suitable relationship between the former and the latter, then conflict analysis can be used to study road safety at reduced cost, with better timing, and even via simulation modelling of facilities that have been designed but not yet built.

The theory and practice of conflict analysis for motor vehicles has been developed over something like a half a century of research. This has evolved to quantitative methods using not just traffic cameras, but also instrumented vehicles, automated data extraction, and theoretical concepts such as time to collision, gap time, gap acceptance, post-encroachment time, and many others. There is no such corresponding body of research for bicycles. Even if there were, it could never be as important to bicycle or pedestrian deaths and injuries as it is for the occupants of cars and trucks: for example, the latter vehicles never topple over at stops or just slip and fall, so that their occupants fracture an arm or strike their heads on a curb. In fact the majority of bicyclist injuries, even those requiring hospitalization, apparently involve only the bicyclist, making conflict analysis entirely or at least largely irrelevant to them.

On the other hand collisions with motor vehicles are major factors in cyclist deaths and injuries, and they are what cyclists worry most about. And even apparently bicycle-only crashes can be provoked by e.g. general fears or specific intimidations, or avoidance manoeuvres leading to loss of control. Thus there are also dimensions of traffic conflicts applicable to bicycling, but either inapplicable or less so to motor vehicle-only conflicts. Nor is every conflict visible or strictly kinematic: consider for example the effects of sudden and loud horn honking or engine revving.

With these fundamental limitations in mind, obviously traffic conflict analysis is a promising method for investigating important aspects of bicycling safety. The theory needs to be developed, so we can figure out what constitutes a high or low rate of conflicts, what types of conflicts figure what way into which accident types, and how vehicle operators and pedestrians cope with them, such as through hypervigilance, or avoidance of the area and thus diversion of problems to a different one.

Not only does the theory need to be developed, but also the methods of data extraction and analysis: the subjective review of traffic camera recordings, typically of low quality, is a mind-numbingly tedious, labour-intensive and error-prone task, that does not scale well.

The work of Monsere et al. (2014), Lessons From The Green Lanes: Evaluating Protected Bike Lanes In The U.S., should be considered a pilot project in this effort, although the authors themselves do not describe it as such.

Monsere et al. aimed to address six questions:

  1. Do the facilities attract more cyclists?
  2. How well do the design features of the facilities work? In particular, do both the users of the protected bicycle facility and adjacent travel lanes understand the design intents of the facility, especially unique or experimental treatments at intersections?
  3. Do the protected lanes improve users’ perceptions of safety?
  4. What are the perceptions of nearby residents?
  5. How attractive are the protected lanes to different groups of people?
  6. Is the installation of the lanes associated with measureable increases in economic activity?

Apart from noting that, as with most sociological research, their survey response rates were dismally low (23-33% overall, counting even only partially completed surveys as full responses), to produce a socioeconomically skewed sample (e.g. the bicyclists being 89% white, 68% male, 82% having at least a four-year college degree, and 48% with annual incomes over $100,000)— this overview of their work considers only the first part of their question No. 2.

Monsere et al. installed video cameras along short bicycle sidepaths (“protected lanes”, “cycle tracks”) constructed between approximately the summer of 2012 and the early summer of 2013 as part of the Green Lanes Project. These were in four U.S. cities, San Francisco (two 0.3 mile paths), Portland (one 0.8 mile path), Chicago (0.8 and 1.2 mile paths) and Washington (a 1.12 mile path; no cameras were installed in Austin, although sociological surveys were conducted there). They did their video recording chiefly at intersections, six in these four cities in the summer and fall of 2013. This was then presumably while the users were still in a cautious or exploratory state, as they got used to the new facilities.

Only 12-18, or in one case 20, independent hours of video were analyzed from each intersection. As each intersection examined was given a unique treatment, results cannot easily be pooled. These are very small numbers.

(This makes for substantially less than 120 hours total. The authors seem to say they analyzed 144 hours of video at intersections. This would mean that some of this total came from multiple cameras examining the same intersection at the same time. The authors do show frame captures from some of their cameras. This observer would find it difficult to correctly identify the conflicts from the views on display.)

As noted following the opening platitude, any facility, no matter how poorly designed, will appear safe if examined over a short enough period of time.

The six facilities examined were all so new (less than or little more than a calendar year old) that there were no injury or death data available for them. (For comparison, the entire city and island of Montreal, with all its thousands of intersections, averages of late about five cyclist deaths and 25-50 police-recorded serious cycling injuries per year.) Thus, there would not have been a way to use even many more hours of recording to examine for any relationship between the surrogate outcomes (conflicts, violations or errant behaviours) and the outcomes of most interest, deaths and injuries.

Further, as this was neither a before-after study nor a comparison with standard intersections, there is no way to know whether the numbers of observed conflicts, violations, or errant behaviours, were themselves high or low.

As to the actual results from this pilot project, the much touted headline was that there were only six minor conflicts found, out of nearly 12,900 bicycle movements through intersections. The most basic problems with this headline are:

1. It is the wrong comparison. The conflict rate has to be the number of conflicts divided by the number of occasions where at least two users capable of conflicting are present, e.g. a bicycle and at least one other bicycle, pedestrian, or motor vehicle. Thus the authors give figures of 7574 turning motor vehicles, but only 1997 turning motor vehicles with bicycles present. The corresponding conflict rates (which they normalize by the products of bicycle and motor vehicle movements, not by the numbers of bicycle movements alone) they give for the individual intersections therefore vary by factors of approximately 3 to 10, depending on which figures are used.

2. Six is the total of observed “minor” conflicts, not the total number of observed conflicts. There were also 379 “precautionary” conflicts with motor vehicles, 216 with pedestrians, and 70 with other bicycles.

3. Besides conflicts, there were numerous violations or other errant behaviours: e.g. 9-70% of bicycles and 7-52% of turning motor vehicles in the various intersection designs used the lanes incorrectly, 1-18% of turning motor vehicles in the various mixing zone designs turned from the wrong lane, 5-10% of motorists turned illegally on red arrows at intersections with bicycle-specific signals, and 7-23% of bicyclists disobeyed their signals.

4. Without any theory or model of how any of these occurrences or their frequencies relate to death, injury, or property damage, and without any before-after or non-sidepath comparison data— not to mention, with the very small numbers of observation hours— there are almost no safety implications, positive or negative. The only concrete result is that one of the local authorities apparently deemed the problem of motor vehicles turning from the wrong lane (18%), straddling lanes (another 17%), or entering the turn lane early (15%) to be so severe that they later removed the intersection treatment and replaced it with another design (at Fell and Baker in San Francisco).

5. The sociological surveys tell another story: one-third of all bicyclists surveyed said they had been involved in at least one near collision on the paths, while 2% experienced an actual collision. 23% had a near collision with turning cars, 1.8% an actual collision with turning cars; 19% a near collision with a pedestrian, and 0.4% an actual collision with a pedestrian.

In short: this is an interesting pilot project, whose methods are impractical for the amount of data collection needed for meaningful safety results. Even with better methods, conflicts are only one facet of the bicycling, and overall safety picture; while road designers and road users, whether bicyclists or motorists, have to consider more than just safety. Convenience, transit time, cost, and greenhouse gas emissions also matter. A cycle track that, like the downtown de Maisonneuve track in Montreal, lies largely dormant in the winter, but delays motor vehicle traffic in the winter and ties it up spring, summer and fall, will be of no help in reducing CO2 emissions. The much touted headline results from this study are selective, overblown, and misleading. Any facility will appear safe if examined over a short enough period of time, and surely 12 to 20 hours each is short enough.

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


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


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


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


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?

The Photoshop School of Traffic Engineering strikes again!

The Photoshop School of Traffic Engineering strikes again, this time in Minneapolis.

For background, please read the Minneapolis blog post: http://www.ouruptown.com/2012/08/potential-cycle-track-coming-to-36th-street

Also please read John Schubert’s comment on that post.

I’ve added a comment too — still in moderation as I write this, and I repeat the comment here, slightly edited and with this introduction.

The location described in the blog post, 36th Street at Dupont Avenue, is shown in the Google map below. If the full image doesn’t appear, clicking to refresh the page will probably fix that. The image is zoomable and draggable, but by clicking on “View Larger Map”, you may enlarge it, look down from different overhead angles, and switch in and out of Google Street View.

View Larger Map

36th Street is part of a grid system. Smaller, lightly-traveled 35th Street is one of several that could instead be configured as a bicycle boulevard (also called neighborhood greenway) like those in Berkeley, Eugene, Portland and Seattle, so bicyclists use the street as a through route while only slow, local motor traffic uses it. That is popular with residents and avoids the problems with sight lines which John Schubert has described.

Now for some comments on the pictures in the Minneapolis blog post. They are examples of of what I call the “Photoshop School of Traffic Engineering”, Or the “Anything Goes” school. Well, anything goes in a Photoshopped picture but not necessarily in reality.

Here’s the first picture from the blog post:

Photoshopped illustration of proposed "cycle track" on 36th Street in Minneapolis

Photoshopped illustration of proposed “cycle track” on 36th Street in Minneapolis

The caption for this photo in the blog post reads “[a] possible cycle track is being considered for 36th Street in Minneapolis.” As we’ll see though, the rendering in the picture is hardly possible.

In the picture, there’s already a sidewalk on both sides but now also a special lane so pedestrians can walk in the street. To make room for this and the bikeway, the blue car in the right-hand travel lane is squished to about 3 feet wide and that lane is about 8 feet wide. The text describes the bikeway as 10 feet wide, but it measures as about 12 feet wide based on the size of the bicycle wheels. 36th Street has a cross street every 300 feet, also entrances to back alleys and driveways in almost every block, but the picture shows maybe one intersection (note crosswalk lines) in the distant background. That is unreal. There’s some need for people to get in and out of all those cross streets, alleys and driveways.

Now, the other picture:

Another Photoshopped illustration of the proposed bikeway

Another Photoshopped illustration of the proposed bikeway

The caption in the blog post reads “[a] rendering of how a cycle track on 36th Street could look east of Dupont Avenue in Minneapolis.” Again, no, it couldn’t.

The bikeway is shown at a more realistic width. I’m not sure though how three travel lanes, a parking lane, 3-foot buffer and 10-foot-wide bikeway fit into a street which now has only two travel lanes and two parking lanes. Also note the car about to turn right across a lane of traffic and then across the bikeway at the one intersection shown. The lane with the closest car in it is shown as a lane of traffic, not a parking lane, or there would be signs and markings to indicate that. Assuming though that it is a parking lane and the turning car isn’t cutting off the closer one, then the closer one is still hiding approaching bicyclists from the turning one, whose driver must look to the right rear to see them as they get closer — remember, they may be traveling at speeds up to 25 miles per hour. The bikeway is outside the field of view of the turning driver’s right-hand rear view mirror. Some vehicles have no windows behind the front seat, and so the bikeway would be in a complete blind spot. I just got back from Montreal where I rode bikeways like this and it’s hair-raising with heavy two-way bicycle traffic in such a narrow space. I also had repeated conflicts with motorists turning across my path, using intimidation to try to make a gap for themselves in the stream of bicyclists. It’s safer to ride on 36th street just as it is now, and a bicycle boulevard would be better choice yet, especially for slower and more timid bicyclists. As John Schubert says in his comment on the blog post, there are better ways to make bicycling inviting.

The proposed design isn’t about improving traffic conditions, for bicyclists or anyone else. It’s about a social agenda: creating the appearance of safety for naive bicyclists to increase bicycle mode share, and making motoring more difficult. Actually, motorists would instead use the smaller parallel streets. Elimination of parking on one side of the street to create the bikeway is unlikely to be popular with residents. Snow clearance also is difficult with barrier posts and parked cars in the middle of the street.

The Montreal bikeways are the subject of a widely-publicized research study claiming a safety advantage, but the study has been demolished, see http://john-s-allen.com/reports/montreal-kary.htm

Why this crash?

The fancy, expensive bicycles and racing clothing are not matched by these cyclists’ bike handling skills.

If you play the video through to the end, you will see that the wheel touch broke 4 of the 8 spokes on the right side of the boutique 16-spoke front wheel.

Detailed explanation:

  1. Boutique wheel, few spokes, spokes necessarily overtensioned, big gaps for things to get in between them.
  2. Rider ahead merged left and slowed (notice backpedaling), oblivious to riding in tight group.
  3. Tri bars and no brake there.
  4. Overlapping.
  5. Spokes broke against QR handle. At this point overlap was by more than half a wheel.
  6. Still a good recovery.
  7. Inability to steer due to unstable front wheel and to need to move hands position to brakes — cyclist heads for ditch.
  8. Attempt to brake on warped front wheel locked the wheel.

Some commenters on the YouTube post have pointed out that the cyclist who crashed was wearing a sleeveless jersey and not wearing socks. This clothing is characteristic of triathletes — who don’t ride in groups while racing and are less likely to learn group riding skills than are road racers. Another point about clothing is that the cyclist wasn’t wearing cycling gloves. He broke his fall with his hands on gravel. Ouch.

A Cyclist Signs Up for Advanced Driver Training

What was an avid cyclist doing in a place like this?

I like to ride my bicycle but sometimes I have to drive.

Over 40 years ago on dirt roads and snow in Vermont, I learned to steer into a turn; to manage the situation when a car loses traction, rather than to blank out or panic.

I shot the video above recently, in a class with hands-on driver training which goes well beyond that. All of the instructors are racers. They test the limits of traction at every turn on the racecourse. But here, they are teaching skills for crash avoidance on the road.

My son took the class with me. He had taken a conventional driver training course and already had his driver’s license, but he had no experience handling a car at the limits of traction.

The InControl course begins with a classroom lecture. Our instructor, Jeremy, explained that driver training is broken in the USA: that over 40% of new drivers have a crash within the first two years; 93% of crashes result from driver error and so, are preventable. He also explained that he would be teaching about steering, braking, hazard perception and avoidance.

Jeremy handed a quiz sheet with 16 questions to check off, true or false. We were told to hold onto our quiz sheets because we would review them later.

The most compelling part of the course is the hands-on practice. It is conducted under safe conditions on a closed course, in a huge, empty parking lot, in cars with a low center of gravity; an instructor is always in the car. As shown in the video, we did the slalom — at first with an instructor driving; then each student took a turn driving. We learned how great the effect of small increases in speed can be on the ability to maneuver. We practiced emergency stops, then swerving while braking; we had the backing demonstration and the tailgating test, as shown in the video.

To learn how to anticipate potential hazards takes time, and experience. The InControl class can discuss this but not teach this. A driving simulator like the ones used to train airline pilots would help to build that experience under risk-free conditions. Video gaming technology is approaching the level that it could do this at a relatively low price. Computers are up to the task, but they would need multiple visual displays and a special “driver’s seat” controller. Lacking that technology, I have traveled many miles with my son, both as a driver and as a passenger, coaching him. His many more miles of experience stoking our tandem bicycle were a fine lead-in.

What did I learn in this class, with my nearly 50 years of experience as a licensed driver? Several things of importance — among them:

  • Despite my decades of experience, I answered several questions on the quiz incorrectly. I’m not going to provide a crib sheet– go take the course.
  • There is a very significant advantage to having different tires for summer and winter use, due not only to snow but also to temperature difference. Winter tires have “sipes” — small grooves –to develop a “snowball effect” — actually picking up snow so it will adhere to other snow, and improving traction. Tires should be replaced when tread is still twice the height of the wear bars.
  • Side-view mirrors should be adjusted wider than I had been accustomed to — so their field of view starts where the windshield mirror’s field of view ends.
  • The National Highway Transportation Safety Administration’s standards for a 5-star safety rating are lower for SUVs than for passenger cars, as a result of industry lobbying (Any surprise?)
  • Importantly, that antilock brakes do more than allow shorter stops. They allow steering during emergency braking, and we practiced this as shown in the video.
  • Most importantly, to me as a cycling instructor, that learning to manage risks is essentially the same for bicycling as for driving a car. The attitude is the same, and hazard recognition and avoidance are similar. One important difference is that a well-trained cyclist’s brain is the antilock braking controller on a bicycle.

As I write this today, my son has driven himself to his classes at the local community college 12 miles away. Like any parent, I cross my fingers every time he goes out the driveway, but I am pleased to report that he has is cautious and calm as a driver and that his driving inspires confidence, with exceptions at a very few times.

I wish he didn’t have to drive. I don’t like the environmental burden it imposes, and I don’t like the risk. If public transportation were at all reasonable, he would be using it. If the college were half as far away, he’d be riding his bicycle at least on days with good weather. For now, his getting a college education wins out over those concerns…

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 Gilham Road raised bike lane, Eugene, Oregon

As a reader has commented on the Gilham Road, Eugene, Oregon raised bicycle lane in response to an earlier post, I’ve decided to follow up with some additional information about it.

Here’s a photo of the lane during installation.

Raised lane on Gilham Road, Eugene, Oregon

Raised lane on Gilham Road, Eugene, Oregon

I thank former Eugene Bicycle Coordinator Diane Bishop for sending me the photo. Her comments in the e-mail which accompanied the photo in February, 2002 are as follows:

I’m curious if you have seen or used any raised bicycle lanes? We installed one this summer and have had mixed reviews from users. Mostly the motorists don’t like it because they are forced to slow down (the road curves around various median islands, etc, and the travel lanes are 10′ wide, dropping the comfortable speed to about 20-25mph). But I”ve also gotten mixed reviews from cyclists. Most really like it, but some are concerned about the slope between the bike lane and the car lane. I’ve attached a photo so you can see what we did. This was taken during construction so we hadn’t done the landscaping, finished the sidewalk, or done the lane line painting. The bike lane stripe is at the bottom of the sloped surface now. The bike lanes are concrete, the auto lanes are asphalt.

The photo was taken at the intersection in the Google map below, looking south.

View Larger Map

Microsoft’s Bing mapping application offers a more detailed view, but you will have to open Bing separately to move around or zoom the view.

Microsoft Bing view of Gilham Road at Ayers Road, Eugene, Oregon

Microsoft Bing view of Gilham Road at Ayers Road, Eugene, Oregon

I responded to Ms. Bishop, as follows:

You asked me for my opinion, so here it is.

As much as political participation is important in our democratic process, I wouldn’t trust either bicyclists’ or motorists’ opinions of the facility. These opinions generally are swayed by perceived self-interest and don’t reflect professional training. Let’s consider the actual operational characteristics and crash rate.

I’m no fan of raised lanes (called “cycle tracks” in Europe). This design is common in early facilities installed in Europe, but now there is a heavy backlash against them, because studies have revealed them to have a much higher crash rate than riding in the street. The German ADFC has strongly opposed them for the past several years, since the study results came out. The ADFC recommends street-level bike lanes instead. [This press release] is typical of the ADFC position.

“Originally, cycle tracks were constructed to protect bicyclists from motor traffic. But since then, the number of studies which show that the risk of accidents is markedly higher on cycle tracks than on the streets has been growing. Bicyclists who are traveling on a two-way cycle track in an urban area on the left side of the street have 11.9 times the accident risk they would have on the streets. The cause of this danger is an incorrect political promotion of bicycling over the past few decades. In the past, travelers were segregated. Consequently, bicyclists and motorists could not see one another. At junctions, the bicycle traffic is directed onto the street, unexpected by the motorists. And so we have the typical urban bicycle accident. A bicyclist traveling straight ahead, struck by a turning motorist, is the most common type of bicycle accident involving a motor vehicle, states Stefan Brandtner, press contact for the All-German Bicycle Club (ADFC) Baden-Württemberg section.”

A survey of research on the accident rates of streets, bicycle paths and sidewalks is available on the Internet. And here are some links to specific studies posted on the Internet. Some (particularly Pasanen and Wachtel-Lewiston) are well-controlled for the same bicyclist population on the different types of facilities, while others are not, and so the difference in accident rates probably reflects to some degree that people who choose to ride on sidewalks generally are less skilled.

The Risks of Cycling by Dr. Eero Pasanen, Helsinki, Finland, higher car-bike collision rate for one-way sidepaths compared with streets, even though pedestrians are prohibited from the sidepaths (very similar to the installation shown). Extremely high rate of car-bike collisions with bicyclists crossing intersection on left sidepath.

Adult Bicyclists in the U.S. by Dr. William Moritz. Relative danger index 16 times as high for sidewalk riding as for major street without bicycle facilities. (Data include all crashes, not just car-bike collisions).

A Survey of North American Bicycle Commuters, by Dr. William Moritz. Relative danger index 5.32 times as high on “other” facilities (mostly sidewalks) as on average of all facilities (mostly streets). Data include all crashes, not just car-bike collisions. Lower ratio than in previous study probably related to typically lower speed and overall higher crash rate of average commuters compared with avid adult cyclists.

Alan Wachtel and Diana Lewiston, Risk Factors for Bicycle-Motor Vehicle Collisions at Intersections (ITE Journal, September 1994). Car-bike collision rate 1.8 times as high for sidewalk riding as for streets.

[The following documents] reach similar conclusions:

Sidewalk Bicycle Safety Issues, by Lisa Aultman-Hall and Michael F. Adams Jr. Bicycle accident rate 6 to 10 times as high as sidewalks as on streets in Toronto. (PDF document. See page 4.)

Toronto Bicycle Commuter Safety Rates, by Lisa Aultman-Hall and M. Georgina Kaltenecker. 4 times as high injury accident rate on sidewalks as on streets (PDF document. See table 5, page 19).

On the facility shown, the bicyclist is confined to the space between the slope down to street level, and the pedal-catching curb on the other side. I don’t know exactly how wide the lane is in the installation shown, but it appears to be no wider than 5 feet, with no shoulders, and with shy distance from the curb at one side and the downslope at the other side, the lane’s effective width is much narrower. The AASHTO minimum for a one-way bicycle path is 6 feet, *with* 2 feet of clearance at either side.

So this facility is not wide enough for one bicyclist to overtake another comfortably, even less so for a bicycle to overtake an adult trike or cargo bike of the type Jan Vandertuin is making (last I knew) in Eugene. Even aside from these examples, the carrying capacity of this lane is seriously reduced by its being raised. When bicyclists ride at street level (with or without a bike lane) they may merge outside the bike lane as necessary if the bike lane becomes crowded. In this installation, they can drop down to the street only at the cost of an uncomfortable and somewhat hazardous descent and ascent over the sloped edge. In wet, or worse, icy weather, or if sand or trash has accumulated at the bottom of the sloped edge, a bicyclist could easily be toppled by it.

The raised lane on each side also is bound to be used for two-way travel, because bicyclists do not perceive it as part of the street, and because it is much less convenient to get to the raised lane on the opposite side than it would be to get to a street-level lane on the opposite side. Left-side travel, as the studies show, greatly increases the risk of car-bike collisions. Some bicyclists would choose to ride on a sidewalk anyway — consider a child who wanted to get from one house to another on the left side of the street in the photo — but I don’t like constructing a facility specifically for bicyclists which encourages this behavior (as opposed to a bike route or street-level bike lane, which encourages right-way travel).

Naive bicyclists may assume that they are being “protected” from overtaking traffic by a raised lane, but the lane will cause more crashes than it prevents — certainly so in the case of single-bike and bike-bike crashes and almost certainly so in the case of car-bike crashes, by constraining the bicyclists’ line of travel and leading to a false sense of security. There appears to be an intersection in the background where the raised lane does not go down to street level before and after the intersection to allow merges (is this correct?). The motorists, than, are constrained to make their right turns from the left lane and the bicyclists, except for those at the ends of the skills spectrum — who are well-trained in vehicular techniques or who, on the other hand, make left turns as pedestrians — are likely to turn left from the right lane.

Often the motivation for a particular bicycle facility design is to affect the behavior of *motorists* rather than bicyclists. The classic reason for this has been to make things easier for motorists by getting bicyclists off the road. But here the goal appears to be to make things *harder* for motorists and slow them down by narrowing the lane width they can use. There are many other traffic calming and enforcement measures to slow traffic down and reduce its volume without constructing a problematic bicycle facility.

Another motive for constructing bicycle facilities is often to encourage people to ride bicycles, but again, there are many alternatives in design, and an unsafe facility which is popular is the kind most likely to lead to crashes!

I DO like gently sloped curbs at the RIGHT edge of the area in which bicyclists ride. With such a curb (commonly used on Cape Cod and called the “Cape Cod berm” here in Massachusetts), the trash, sand, water and ice problems still occur but at least most of the time a bicyclist who has strayed off the road can go safely up over the curb.

It appears that there is also a drainage issue. With no storm grate in the bike lane, and a curb at the right side, the lane will only drain if it slopes toward the street. It may be properly sloped now, but concrete slabs tend to tilt after a few years.

Essentially, I don’t see any significant difference between this facility and a sidewalk as far as bicyclists are concerned, other than that pedestrians have a separate sidewalk. I favor traffic calming measures in residential areas, with bicyclists traveling on the street, wide outside lanes and sometimes bike lanes at street level (though bike lanes are often installed where they create turning and crossing conflicts, and other solutions would be preferable); also bicycle paths away from roads to fill in the “missing links” in a bicycle route network, as discussed in the Oregon bicycle plan. This is my honest opinion and I hope it doesn’t upset you too much!

And in turn, Ms. Bishop replied:

On your raised bicycle lane response: no, you didn’t upset me. I’m not sure I agree with some of your comments, but I’m here and can see the lane and use it and you haven’t had that chance. Now that we have had it installed for a while and I’ve had a chance to ride it on several occasions, I’ve begun thinking we probably won’t keep this in our “toolbox” of street treatments. However, there are some things that seem to be good. I haven’t done a video study of the lane usage yet because it was completed so late in the fall last year. I’ll be doing that this spring. If I come up with
anything useful, I’ll let you know.

We don’t get snow or ice here (well, MAYBE a sprinkling of snow that lasts about 1/2 hr. once a year) but we do get a lot of rain. I was concerned about the sloped surface being slippery, but I’ve found it surprisingly easy to ride in the rain. I’ve also tested running up and down the slope pulling various trailers and they track as smoothly I can’t tell the difference from riding on a flat surface, even when one trailer wheel is over the edge while I’m still on the flat bike lane surface. One of the concerns raised by the neighbors (that I haven’t seen materialize) was that the kids would be out there using the sloped surface for playing with their bikes and skateboards.

I think you may be right about less competent cyclists not thinking about merging down into the auto lane to make their left turn. I hadn’t anticipated that when we decided to build the lanes. But I don’t think it will lead to more 2-way riding for 2 reasons: we have sidewalks for those you mentioned who would only be traveling a few houses away and those sidewalks are more accessible; and also because the traffic is relatively light on the street where we have the raised bike lanes (its a neighborhood collector).

For your suggestions on why we might have tried the design, actually you were right about the traffic calming interest…some of our folks were looking for ways to reinforce other traffic calming methods they built into the project. However, *I* was more interested in trying out a bike facility that might appeal more to children in order to get them off the sidewalks (which I agree with you are much more dangerous than the street). Our hope was that we could get them out in the street area where they will be seen by the motorists and slightly separated so they would be willing to try it. Raising them slightly higher seems to have the added benefit that motorists can see them better. I”m not sure we really accomplished all that.

So, thanks for your ideas. Like I said, I don’t think we are going to do that design again, but it was an interesting experiment. We want to make this community even more bicycle-friendly than it is, so are willing to try different approaches. Unfortunately I had very little time to research the design and, while [State of Oregon Bicycle coordinator] Michael Ronkin had it in the state bike/ped plan, he couldn’t suggest people or communities to check with in Europe.

And in turn, I replied:

Thank you very much for your reply. From your description, the sloped surface between the bike lane and the roadway appears to be less severe than it appears in the photo.

On another topic: there is a very interesting citation of a rather old Eugene study in a paper by John Williams, Alex Sorton and Tom Walsh. Dr. Sorton has told me that the paper includes data on the crash risks on streets, sidewalks and off-road paths. I would be most interested in knowing more about the study and if possible, obtaining a copy of it. I would be willing to pay for copying expenses and offer a service in return: conversion of the study into computer-readable format as I have done with a several other studies including, most recently, the classic 1976 Bikecentennial study — which I have posted it on my site.

This inquiry led to Ms. Bishop’s sending me a copy of the 1979 Eugene bicycle plan report, which I scanned and posted on the Internet — but that’s another story.

Mountable curbs

Mountable curbs have been suggested as a way to separate bike lanes or so-called “cycle tracks” from the rest of the street.

I am not in favor of such curbs. After all, any obstacle has hazard potential, and a mountable curb can have more than you would imagine.

As a cyclist rides along a mountable curb, tire “drift”, the slope and the offset front-tire contact patch make the bicycle hard to steer, so it must be held in a straight line by a continual effort. A similar issue with a different cause is discussed here.

Worse, if a mountable curb is slippery, it is no longer mountable, though it may deceptively still appear to be. The resulting fall may be a skidding-type fall or a diversion-type fall, in which the bicycle’s front wheel is swept to the side.

Trash, sand, snow or ice can accumulate along the curb. Installation of a curb-separated “cycle track” on a conventionally crowned roadway would require sloping the road surface away from the new curb to avoid this problem.

Even this unusual measure would not make snowplowing or street cleaning any easier, with an abrupt longitudinal change in elevation in the traveled way.

An approach used in Copenhagen is described here — a second line of drains at the curb (in the case shown, not mountable). The drains carry away standing water but does not solve the problems with trash, sand, refreezing water in the added, new gutter, snow clearance or street cleaning.

Cambridge, Massachusetts bicycle coordinator Cara Seiderman has shown a photo of a machine with a large, cylindrical, horizontal rotating brush used to clear snow from Copenhagen facilities. Perhaps this answers some of the issues with snow clearance and perhaps it also is used for street cleaning, but the expense is considerable, and the need for such equipment may not even be considered when a facility is constructed.

Snow clearance and ice melt issues on the 9th Avenue facility in New York City are described here; this is a barrier-separated rather than curb-separated facility, but the issues are similar. The bikeway here is wide enough that conventional snowplows could be used, but refreezing of meltwater from the windrow of snow between the bikeway and the street required heavy salting, and salt rusts bicycles.

So, is the prohibition of a barrier between a bike lane and the rest of the street in the AASHTO bike guide arbitrary? Does it only reflect issues with cyclists’ being able to enter and leave a bike lane, which can be addressed with a mountable curb? Not hardly.

Promotion of curb-separated bikeways, without considering the technical issues,or with “band” aid solutions such as mountable curbs, is all too typical of much bicycling advocacy.

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.