Tag Archives: pedestrian
The dashcam video in the recent Tempe crash which killed a woman walking across the street with a bicycle has now been released.
To me, it is quite clear that the human driver was dozing off or distracted and that the vehicle’s sensors failed to register that the pedestrian — walking with a bicycle broadside to the road, a very robust infrared and radar target, and crossing empty lanes before reaching the one with the Uber vehicle — was on a collision course. The vehicle had its low-beam headlights on when high beams would have been appropriate, the headlights were aimed low (probably a fixed setting), and the pedestrian’s white shoes don’t show in the video until two seconds before impact, that is, at a distance of about 60 feet at the reported 40 mph.
Braking distance is about 80 feet at 40 mph, and reaction time for a human driver adds about another 60 feet. An automated system with radar and infrared should have noticed the pedestrian sooner, had a shorter response time, and stopped the vehicle. Human eyesight is much better than a dashcam’s at night and the human driver might have seen the pedestrian earlier and avoided the crash if she had been paying attention. But also, the bicycle had no lights or side-facing retroreflectors which might have shown up much earlier and alerted optical or infrared sensors or a human driver, and the pedestrian somehow chose to cross an otherwise empty street at precisely the time to be on a collision course.
So, the human driver and vehicle’s sensors failed miserably. We can’t allow automated vehicles (and human drivers) to perform at the level shown in this video. We do need to make greater allowances for pedestrians, bicyclists, animals, trash barrels blown out into the road, etc.
Several people have offered insights — see comments on this post, and also an additional post with a description and history of the crash location.
Dutch roundabouts have received a lot of publicity, notably here: https://bicycledutch.wordpress.com/tag/roundabout/
Roundabout design in the Netherlands has seen a long process of trial and error. A design used until bicyclists complained strongly enough about it placed the bikeway away from the circular roadway, but cyclists were required to yield. Here is an explanation of Dutch roundabout design developments.
The current preferred design places the bikeway away from the circular roadway, and motorists are required to yield, as shown in this video below. That clears up yielding issues.
Here is a video of a roundabout outside the city of s’Hertogenbosch, put forward as an example of good design.
There is a long discussion of this roundabout, among others, on Facebook.
This is a rather large roundabout at the intersection of major highways, and with moderate deflection on entry or exit. Looking here in Google Maps, it’s clear that the highway in the background at the left is a bypass around the city of s’Hertogenbosch — though not a limited-access highway like the one which appears in the distant background in the video.
This roundabout was constructed in connection with the new bypass road around the city. Google Street View from 2009 shows the roundabout under construction. A sidelight on this observation is that Dutch practice does consider motor traffic. Two of the legs of the intersection at the roundabout are new roads being constructed at the same time.
I’ve been told by a knowledgeable person that the bikeways on either side of the highways are supposed to be one-way, but the only destinations along these bikeways are at intersections — reducing the temptation to ride opposite traffic.
The design requires a lot of space because the circular bikeway is much larger than the circular roadway. The roundabout is outside a city, but nonetheless, it appears that several houses had to be demolished or moved to make way for this roundabout.
The installation here places separate bikeways (red asphalt) and walkways (paver blocks) outside the circular roadway. Bicycle traffic shown in the video is light. If bicycle traffic were heavy, it would result in congestion of motor traffic because motorists yielding to cyclists could not enter or exit the roundabout. Having a path (or for that matter, crosswalks) around the outside of a roundabout obviates the main advantage of the roundabout, that traffic can keep moving. Only grade separation would avoid this for both bicyclists and pedestrians. Motor vehicles and bicycles sharing the roadway would avoid the bicyclists’ causing congestion, but would not be as attractive for bicyclists lacking in skill and confidence.
If you look at the video full-screen, you can see a number of details which are not evident in the small window on this page. I am most interested in the interactions and negotiations for right of way, which are the central issue with mobility and safety in any intersection which is not traffic-signal controlled.
Expectation in the Netherlands is that motorists will yield wherever they see shark-tooth markings. The path around the outside of the roundabout is brought out to the entry and exit roads at a right angle and far enough outside the roundabout so that motorists will be able to see approaching bicyclists. Ohio resident Patricia Kovacs has investigated roundabouts in that state and demonstrated that motorists don’t even yield to pedestrians. She has posted some comments about roundabouts on this blog and in the Facebook thread mentioned earlier.
Some cyclists in the s’Hertogenbosch video are shown looking to their right as they pass paths coming in from their right, for example at 0:55 and 2:25, but many are shown not turning their heads to look for conflicting motor traffic. That is to say, they are putting their complete faith and trust in motorists to yield to them, which is a comment on Dutch expectations for motorist conduct. There is an especially stunning example of this at 1:59, where a cyclist powers through an intersection as motorists approach from the left, inside the roundabout, and the right, entering it. However, at 6:07, a motorist stops abruptly at an exit to the roundabout as a fast cyclist comes around from the right.
One cyclist leaves the roundabout on the left side, opposite the intended direction, at 1:38 in the video. Another is riding around the roundabout clockwise at 2:40 and apparently while talking on a mobile phone.
At 2:34, a motorist is shown slowing to yield to a cyclist who turns right rather than to cross the exit of the roundabout. With no lane changing or negotiation betwen motorists and cyclists, the motorist did not have a way to know which way the cyclist would go.
Cyclists carry various objects in their hands or on the handlebars. At 6:40, a cyclist is carrying something which looks like a hockey stick.
At 7:18 a young woman has a disabled bicycle and is walking.
Now let’s look at some other Dutch roundabouts.
A roundabout inside s’Hertogenbosch, here, has the bikeway immediately adjacent to the circular roadway, so that cyclists are hidden directly behind — not next to — exiting vehicles.
Here’s the video of the roundabout. The video shows motorists required to yield to cyclists in spite of this right-hook threat.Are the cycling facilities safe, as claimed? Or if safety is achieved here, is it maybe achieved in another way? You decide.
The description of the video indicates that this roundabout is rather new. Its design appears to be restricted by the small available space at an urban intersection.
Some notable interactions:
At 0:20, a car brakes rather abruptly. Shortly thereafter, a motor scooter passes through the roundabout on the roadway.
At 0:30 and again at 0:53, a car blocks the bikeway to allow a pedestrian to cross in a crosswalk which is just outside the bikeway.
Most bicyclists are not paying any attention to the traffic in the roundabout, At 0:45, a bicyclist is looking down at a cell phone, but at 0:50, 1:10, 1:29, 1:53, 2:03 and 2:10, and a few additional times, bicyclists perform a shoulder check. The one at 2:03 does this while also carrying a cell phone in one hand.
At 1:49 and again at 2:20, there is a motorcycle in the bikeway, waiting along with bicyclists to enter the roundabout, and there is a bicyclist standing over his bicycle, facing opposite the direction of traffic. It appears that he is having a conversation with the motorcyclist and a couple of pedestrians. They are blocking the crosswalk.
At 2:49, a motorist stops in the roundabout to yield to a bicyclist who does not cross, but instead turns right. The bicyclist gives a right-turn signal, but too late for the motorist to react, and in any case, a prudent motorist would not risk that the bicyclist would go straight even though signaling. The design of the roundabout does not make the bicyclist’s intentions obvious.
At 2:58, a bus barely outpaces a bicyclist through the roundabout. The bicyclist turns right, but the bus driver has no way to know that he will. The bus driver is either very highly skilled at judging the bicyclist’s speed, or reckless. The bicyclist would have had to yield to the bus if going slightly faster and continuing around the roundabout.
Starting at 3:00, several bicyclists enter traveling the wrong way on the bikeway or sidewalk. Some turn right but others pass close to a doorway which a pedestrian has just exited, and a blind corner, and cross from right to left in the crosswalk or bikeway. An articulated bus enters the roundabout and these bicyclists pass behind it. Other bicyclists traveling counterclockwise around the roundabout will have to yield to the long bus, though this occurs outside the field of view of the video.
At 3:45, bicyclists share the bikeway around the roundabout with a skateboarder and motor-scooter rider.
Almost all the bicyclists are pedaling about 40 rpm. At thsi cadence, it is possible to produce enough power to ride only slowly, and it is not possible ot accelerate smartly.
Here’s a roundabout where bicyclists go around square corners: http://goo.gl/maps/lxfc2
And a little roundabout with advisory bike lanes at some of the entrances: http://goo.gl/maps/HK908
In the so-called “shared space” roundabout in Drachten, cyclists share space with pedestrians. The meaning of the term “shared space” is very different here from its more usual meaning, that motorists, bicyclists and pedestrians all operate in the same space. In the Drachten roundabout, bicyclists and pedestrians share space — as on shared-use paths in the USA — but are strictly separated from motor traffic except in crossings, as in the other Dutch roundabouts. The space around the margins of the Drachten roundabout also serves as a pedestrian plaza.
I’m poking around in YouTube and Google maps. Here’s a roundabout in YouTube — http://www.youtube.com/watch?v=EXUF97p8fXQI — location not given, as is usual in such promotions, but I found it in Google Maps by searching on the name of one of the businesses nearby: http://goo.gl/maps/Jd2ED. A special feature made the roundabout practical: the buildings are set far back at a 45-degree angle on each corner. The circular bikeway around the outside makes it possible for motorists to see cyclists in order to yield (though motorists don’t always, as the video shows) and greatly adds to space requirements, which already are large for a roundabout. There wouldn’t be room for such a roundabout at many urban intersections.
Here’s a blog post which includes the video just described and others of the same roundabout, and describes different types of Dutch roundabouts. http://bicycledutch.wordpress.com/2013/05/09/a-modern-amsterdam-roundabout/
Another roundabout in Amsterdam is of the spiraling Turbo Roundabout design, with a path close around the outside and scary sight lines which place a cyclist too far to the right to be in view of a motorist exiting the roundabout: http://goo.gl/maps/fQybJ and street view, http://goo.gl/maps/LU1ww . Traffic signals have been placed at the exits to mitigate these conflicts. This is a triple roundabout with a tramway going around the inside, also requiring traffic signals.
The left and center roundabouts in this overhead view, http://goo.gl/maps/Q3jIy also are of the bikeway-around-the-outside type: but the rightmost roundabout, in a wooded area, is of the newer type.
Dutch roundabouts are of several types for motor traffic, but the major difference for bicyclists is whether they travel around the outside of the roundabout, or there are grade separations. There are no examples like the small modern roundabouts and neighborhood traffic circles in the USA, where bicyclists share the roadway with motor vehicles.
Here is an example of grade separation: https://bicycledutch.wordpress.com/2011/05/26/multi-level-roundabout-the-safest-solution-for-a-junction/
And here is a showcase example of grade separation — replacing an installation much like the one shown in the first video embedded in this post : https://bicycledutch.wordpress.com/2012/08/23/spectacular-new-floating-cycle-roundabout/
Roundabouts are expensive and take up a lot of space. Many of the promotions we are seeing of Dutch facilities ignore these limitations and the compromises they exact and/or celebrate the newest and most impressive examples.
The Brooklyn Bridge, one of the engineering wonders of the world, opened in 1883 and is still in full service. (Highly recommended: David McCullough’s book The Great Bridge…) Traffic on the roadways when the bridge opened consisted of horseback riders, animal-drawn vehicles, trolley cars and a few high-wheel bicycles. The elevated, central promenade of the bridge was designed for pedestrians. With the advent of motoring, the trolley line was removed and bicyclists were relegated to the promenade. The bridge had stairs until 1982 when it was renovated and bicycling activists succeeded in getting them replaced with ramps. The activists were able to point to the stairs’ as an accessibility issue and also that a stampede on them had killed people shortly after the bridge opened.
The promenade is narrow and often crowded. Though there is a line designating bicycle and pedestrian space, neither space is sufficiently wide. Pedestrians like to stand on both sides, to look out.
Prudence and caution are in order. The bicyclist in the video below is exhibiting neither. Bicycling Magazine has more sympathy for him than I have.
Will bicyclists someday be allowed to ride on the roadway again? A good case could be made for barrier-separated bikeways on the bridge, but removal of lanes for motor traffic would increase congestion and face fierce opposition. At one time, elevated trains ran between the ends of the bridge on rails at the level of the promenade. They were replaced by subway lines which run in tunnels under the river and extend farther. A path could be installed where the trains once ran. In fact, the City is looking into this. Historical status of some elements of the bridge is questionable, as much has changed over the years including removal of much that was original. The superstructure of the bridge evolves to meet current needs, demands, preferences and financing, while its underlying structure stands unchanged, a monument to the genius of its creators and the years of hard work and sacrifices of life and health which went into its construction. Onward to the next stage, with an improved bikeway…
Here’s a quick review of an article by Michael Andersen of the PeopleforBikes Green Lane Project about the City of Boulder, Colorado’s removing what he calls a “protected bike lane”. I prefer to call it at barrier-separated on-street bikeway, avoiding a value judgment. Let’s see what the article in fact establishes.
According to the graph (copied above) and numbers in the article, the installation achieved a major reduction in collisions between motor vehicles at the expense of a 2.5 time increase in motor-vehicle-bicycle collisions. The article states that bicycle volume went up by 54%, and so the car-bicycle crash rate went up by about 1.6 times. Most car-bike crashes in urban areas involve crossing and turning movements. Forcing motorists to cross a bikeway to enter a travel lane, and forcing bicyclists and motorists to start turns from the wrong side of each other, make these crashes more difficult to avoid.
But the story gets more interesting if you click on the article’s link to city data. The left pie chart at the bottom of the city-data infographic shows crashes per year before the installation and the right pie chart, crashes per week following the installation. There were, on average, 11.3 car-bike crashes per year before the installation and 3 in 8 weeks, about 20 per year, afterward. That comes out to an increase of about 1.7 times, but the afterward sample is very small (3 crashes) and seasonal variation isn’t accounted for. The comparison has no validity.
Now look again at the graphs in the article. They don’t accurately reflect these numbers. The “before” bar reports about 0.15 car-bike crash per week or 8 per year, not the 11.3 per year in the pie chart, and so the graph shows an increase in bicycle crashes even greater than the numbers would suggest .
So, to sum up, the article reports a reduction in car-car crashes, but a large increase in car-bike crashes — while defending the bikeway as “protected” and failing to note that there isn’t enough “after” data to produce any statistically valid comparison.
Oh, and there’s also this, on the second page of the infographic:
“The bicycle volume increase along the corridor is consistent with the increase the city typically sees when school is back in session.”
The cyclist counts, unlike the crash counts, are robust. About half the increase is attributable to the school’s being back in session, not to installation of the separated bikeway — a point which Andersen neglects to mention.
To sum up:
What does the article say about the safety of the Boulder facility? Nothing. No conclusion can be drawn from the data, but despite that the Green Lane Project shot itself in the foot with a graph showing a large increase in bicycle crashes.
What does the say about bicycle use? Maybe an increase of 20% or so due to installation of the bikeway, though some of that may only have been transferred from another street.
What does the article say about the quality of Green Lane Project journalism? I think that I’ve made my point but you can answer that for yourself.
Bob Sutterfield writes:
I don’t ride fast so I can participate safely in traffic. I participate in traffic so I can safely ride fast enough for my needs.
If I were to ride in the gutter, on the bike path, in the door zone, on sidewalks and cycle tracks, etc. I could reduce my risk (probably to an acceptable level) by traveling slowly – at near-pedestrian speeds. That slower speed would give me more time to react to the hazards present in those environments.
But I use my bike for purposeful travel. I don’t have time in my day to travel as far as I need to go, if I were constrained to moving only at near-pedestrian speeds. In order to get where I’m going in a practical amount of time, I need to be able to ride at the speeds I’m capable of sustaining on a bicycle. And I need to do it more safely than if I were in the gutter or on a bike path or in the door zone – I need the safety and convenience of the travel lane. That speed is what the travel lane is designed to accommodate, and that’s what the ordinary traffic laws are designed to enable.
If my choice of travel by bicycle is restricted to hazardous areas like gutters and bike paths and cycle tracks, I’ll choose another way to travel – something motorized so I don’t suffer those restrictions.
Here’s a video showing a bicycle ride on a constant mile-long upslope, at speeds of 10 to 12 miles per hour (16 to 20 km/h), on a suburban 4-lane speedway with narrow lanes and no shoulders, the most challenging street in the community where I live. Motor taffic was very light, and auite fast. Points made:
- Lane control is not about riding fast: it is about controlling one’s space.
- Lane control is necessary so motorists will overtake at a safe lateral distance on a street with a narrow right-hand lane.
- By requiring motorists to make full lane change, lane control lets a cyclist with a rear-view mirror confirm well in advance that motorists will overtake with a safe lateral distance.
- With the light traffic on a multi-lane street, a slow bicyclist does not cause any significant delay to motorists.
- Most motorists are cooperative.
- A few motorists are abusive — even though they can easily overtake in the next lane — but they too overtake safely.
- American traffic law supports lane control.
There’s plenty of confusion to go around here.
Deputy: “I don’t care, you’re right in the middle of the road.” No, the boarder was on the shoulder, at least in the part of the video the TV station broadcast.
Was that legal? Bicycling is allowed on shoulders in many states. I couldn’t find anything on that on the Utah legislative site section on bicycles, http://le.utah.gov/xcode/Title41/Chapter6A/41-6a-P11.html.
But the man was on a skateboard, not a bicycle. Under Utah law, the skateboard is defined as a vehicle, last definition here: http://le.utah.gov/xcode/Title41/Chapter6a/41-6a-S1105.html and so, under the law, the skateboarder should have been in the travel lane, not on the shoulder or a sidewalk, if any, as little sense as that may make.
So, the officer’s charge was false. If the boarder were defined as a pedestrian, then shoulder use in the absence of a sidewalk would be legal if the boarder was traveling opposite the direction of traffic (he wasn’t), — not that this is sensible when it would have required crossing to the far side of a multi-lane road. http://le.utah.gov/…/Title41/Chapter6A/41-6a-S1009.html.
There is a sidewalk, as shown in Google Earth and Street View images.
The TV station video is edited at 00:25. It doesn’t show the entire conversation between the deputy and the boarder before the boarder attempted to flee — so we don’t know about an opportunity to comply. Other question is how the boarder could comply if there was nowhere to go except up and down a road bordered by vegetation. The deputy ran after the boarder and attempted to stop him. Probably better to let him go. The boarder fought the deputy, violently. Not smart at all.
Ohio cyclist Patricia Kovacs posted an e-mail asking some questions about roundabouts:
Ohio engineers are telling us to use the inner lane for left turns and U turns. Both the FHWA [Federal Highway Administration] and videos available on our local MPO [metropolitan planning organization] website say this. I shared this when we asked for updates to Ohio Street Smarts. If the FHWA and MORPC [Mid-Ohio Regional Planning Commission] are wrong, then we need to fix it.
Would you review the 8 minute video on the MORPC website and let me know what I should do? If it’s wrong, I need to ask them to update it. This video was made in Washington and Ohio reused it.
Looking further into the problem, I see a related practical issue with two-lane roundabouts, that the distance between an entrance and the next exit may be inadequate for a lane change. The larger the roundabout, the longer the distance in which to change lanes, but also the higher the speed which vehicles can maintain and so, the longer distance required. I’m not sure how this all works out as a practical matter. Certainly, turning right from the left-hand lane when through traffic is permitted in the right-hand lane is incorrect under the UVC [Uniform Vehicle Code], and results in an obvious conflict and collision potential, but I can also envision a conflict where a driver entering the roundabout does not expect a driver approaching in the inside lane of the roundabout to be merging into the outside lane.
All in all, the safety record of roundabouts is reported as good (though not as good for bicyclists and pedestrians), but I’m wondering to what extent the issues have been subjected to analysis and research. When I look online, I see a lot of roundabout *promotion* as opposed to roundabout *study*. Perhaps we might take off our UVC hats, put on our NCUTCD [National Committee on Uniform Traffic-Control devices] hats, and propose research?
This post was getting long, so I’ve placed detailed comments on the Ohio video, and embedded the video, in another post. I’m also working on an additional post giving more examples, and I’ll announce it here when it is ready.
Here are some stills from the video showing the conflict between through traffic in the outer lane and exiting traffic in the inner lane.
First, the path for through traffic:
Next, the path for left-turning traffic:
Now, let’s give that picture a half-turn so the left-turning traffic is entering from the top and exiting from the right:
And combining the two images, here is what we get:
The image below is from the Manual on Uniform Traffic Control Devices, and shows similar but not identical lane use. The arrows in the entry roadways direct through traffic to use either lane.
Drivers are supposed to use their turn signals to indicate that they are to exit from the inner lane — but drivers often forget to use their signals. Safe practice for a driver entering a roundabout, then, is to wait until no traffic is approaching in either lane, even if only entering the outer lane.
A fundamental conceptual issue here is whether the roundabout is to be regarded as a single intersection, or as a series of T intersections wrapped into a circle. To my way of thinking, any circular intersection functions as a series of T intersections, though it functions as a single intersection in relation to the streets which connect to it. Changing lanes inside an intersection is generally prohibited under the traffic law, and so, if a roundabout is regarded as a single intersection, we get the conflicts I’ve described.
Sometimes, dashed lines are used to indicate paths in an intersection, when vehicles coming from a different direction may cross the dashed lines after yielding right of way or on a different signal phase. More commonly, a dashed line indicates that a driver may change lanes starting from either side. The dashed lines in a two-lane roundabout look as though they serve the second of these purposes, though they in fact serve the first. These are shorter dashed lines than generally are used to indicate that lane changes are legal, but most drivers don’t understand the difference.
That leads to confusion. If you think of the roundabout as a single intersection, changing from the inside to the outside lane is illegal anywhere. If you think of the roundabout as a series of T intersections, changing lanes should occur between the entries and exits, not opposite them –though there is also the problem which Patricia mentioned, that a small two-lane roundabout may not have much length between an entry roadway and the next exit roadway to allow for a lane change. That is, however, much less of a problem for bicyclists than for operators of wider and longer vehicles. It would be hard to construct a two-lane roundabout small enough to prevent bicyclists from changing lanes.
My practice when cycling in conventional two-lane traffic circles — and there are many in the Boston, Massachusetts area where I live — is to
- enter from the lane which best leads to my position on the circular roadway — either the right or left lane of a two-lane entry;
- stay in the outer lane if leaving at the first exit;
- control the inner lane if continuing past the first exit;
- change back to the left tire track in the outer lane to prepare to exit.
That way, I avoid conflict with entering and exiting traffic in the outer lane, and I am making my lane change to the right in the slow traffic of the circular roadway rather than on the straightaway following it. This is what I have found to make my interactions with motorists work most smoothly. Why should a bicyclist’s conduct in a roundabout be different?
It is usual to be able to turn right into the rightmost lane of a multi-lane roadway while traffic is approaching in the next lane of that roadway. I don’t know of any other examples in road design or traffic law in the USA where a motor vehicle is supposed to turn right across a lane where another motor vehicle is entering. Bike lanes are sometimes brought up to intersections, though the laws of every state except Oregon require motorists to merge into the bike lane before turning. The illustration below, from Dan Gutierrez, depicts the problem.
Applicable sections or the Uniform Vehicle Code are:
- 11:304 (b) — passing on the right is permitted only when the movement can be made in safety.
- 11:308 (c) — a vehicle shall be driven only to the right of a rotary traffic island.
- 11:309 (a) — no changing lanes unless it can be done in safety
- 11:309 (d) — official traffic control devices may prohibit lane changes
- 11:601 (a) Right turns – Both the approach for a right turn and a right turn shall be made as close as practicable to the right-hand curb or edge of the roadway.
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:
- Do the facilities attract more cyclists?
- 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?
- Do the protected lanes improve users’ perceptions of safety?
- What are the perceptions of nearby residents?
- How attractive are the protected lanes to different groups of people?
- 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.