By John Brooking, 5 December 2012 at 8:01 am
This is the second installment in a three-part series by guest author, John Brooking (read part one here);
Reply by Cameron Puetz 7 hours ago – ChainLink Forum
The manufactured conflict with right turns is the main reason I don’t like protected lanes as they’ve been implemented so far. In my opinion, improving intersections should be the main focus of bike infrastructure projects.
The rules of the road for general traffic have been in development for about 100 years now. One of the earliest pioneers of traffic law was William Phelps Eno, who started writing the first traffic rules for New York City in 1903, well before cars were common. He remembered as a child witnessing a traffic jam consisting of “about a dozen horses and carriages” in 1867, and observed that “all that was needed was a little order to keep the traffic moving”. He was also purported to have believed automobiles would be a passing fad. Thus, he developed rules of the road for “traffic” in general, in which he explicitly included bicycles and bicyclists.
Of course, we now know he was wrong about cars being a passing fad. As automobiles were officially declared to be vehicles and became more popular, traffic engineers had to put more thought into mitigating the public danger posed by the new invention’s speed and mass. One field that developed was the study of “human factors”, the limitation of human perception and mental processing, during such focused tasks as driving a car.
One foundational principle of the rules of the road is what some engineers call “destination positioning”. This is simply the practice of choosing a road position at intersections based on where you are going. If turning right, do so from close to the right side or curb. (This is seen as early as Eno’s rules.) If turning left, merge over to the center of the road (the left side of your half). If going straight through, be somewhere in the middle.
“Destination positioning” at intersections may be compared to “speed positioning”, which calls for slower vehicles to stay to the right between intersections. Between intersections, that makes sense.
Destination positioning at intersections means that the following configuration of general travel lanes would be a poor design, and not something any traffic engineer would do (see Figure 1 image in photo gallery below):
It’s easy to see how this could cause car crashes due to permitting right turning traffic to cross straight-through traffic. When drivers make a right turn, they already need to look to their left for traffic in the lane they are turning into, to the front for oncoming traffic taking a left turn into the same lane, and to their immediate left and right for pedestrians. If they also needed to look behind them to the right, that’s about 3/4 of a circle they need to scan continuously as they are turning.
Scanning such a large angle allows a lot of chance to miss something while looking somewhere else. Yet a motorist turning right from the left lane here would have to look, because the person making a lane change always has to yield to others already in the other lane. This design basically allows merges to happen right at the intersection, instead of before.
Because of all the confusion this would create, no traffic engineer would ever stripe general travel lanes this way. Intersection lanes are always striped to conform to destination positioning.
Except for bicycle lanes, that is (see Figure 2 image in photo gallery below).
When a lane for through bicycles is striped all the way to an intersection, to the right of a lane where other traffic could turn right, how is that different from the general lane configuration in Figure 1? Only the width of the right lane. But all the other problems are still present – the wide angle required for right-turning drivers to scan, and the chance to easily miss an approaching bicyclist on the right.
It’s even harder to see a bicyclist in a narrow lane at a steeper angle behind you than it is to see another car in the middle of a normal lane. They are easily blocked from view by the cars behind you. The motor vehicle could have large blind spots (trucks) that physically prevent seeing large areas to the rear. Finally, the phenomena of “inattentional blindness” and “Saccadic masking” also contribute to the chance that a driver is more like to miss seeing a bicycle on the periphery than another car in a full-sized travel lane.
These are all problems of human perceptual and operational limitation that cannot be fixed by just granting bicyclists the legal right of way in a bike lane. Increasing the penalties for violation may raise awareness, but still ignores basic facts about human ability.
If a motorist passes a bicyclist on the approach to the intersection, when speed positioning is still in effect, of course the motorist needs to judge whether there is enough time to turn right before the bicyclist arrives, with or without a bike lane.
But when a bike lane is present, it adds behavioral cues that do even more to encourage mistakes. Motorists are discouraged from merging to near the curb to turn even if there is no bicyclist in the bike lane, and cyclists approaching stopped or slowed traffic from behind are encouraged to pass on the right, even past traffic that may not have passed them first. Critics of this bike lane intersection design refer to this as a “manufactured conflict”, a conflict which is encouraged, if not created, by the infrastructure.
Separated cycle tracks actually worsen the intersection conflict, by physically separating the bicycle and motor traffic from each other until close to the intersection. Merging opportunistically in a gap is impossible, replaced by the requirement to merge at a single designated place, where it may or may not be possible depending on the traffic at the time. Barriers can further diminish the ability of motorists and cyclists to see each other on the approach. Unless the intersection at the end of a cycle track is controlled separately for bikes and cars using a separate bikes-only signal phase, cycle tracks (and bike boxes) practically set up right hook conflicts.
A conflict similarly exists with bike lanes that are too close to parked cars.
We know doorings can be dangerous to cyclists, sometimes fatal. Yet as Brent points out in the comments section of his page, many Chicago bike lanes are in the door zone. Why is that? Certainly anywhere on the roadway carries with it the chance of making a fatal mistake, but what other facility persuades its users by its very design to intentionally put themselves in that kind of danger?
Motorists instinctively drive away from the doors, but cyclists have been trained to avoid the general travel lane at all costs, even to the point of riding in the door zone, and the lanes encourage this. The rules of the road are intended to protect road users, but door zone bike lanes guide bicyclists exactly where to ride to be hit by opening car doors. According to this study, over a dozen cyclists are doored every month in Chicago, on average (see Figure 3 image in photo gallery below).
In the final installment, we will discuss the role of law and education, and how all of this can work to together to influence safety for better or worse.
Scroll down for image gallery.