The Cambridge, Massachusetts
Graph of bicyclist wheel tracks for bike lane
installation near Columbia Street. I have added the
descriptive comments in small print. The horizontal
bar which I have added at the bottom indicates
the real limits of the "door zone" for bicyclists
overtaking typical passenger vehicles.
|A statement on page 11 of the report contradicts the others as well as the intent of
the graph coloring by telling the uncomfortable truth:
In other words, the wheel path would be at least 11 feet from the curb for bicyclists to be outside the door zone, just as I have described. Except for this one lapse, the conclusions of the report do not reflect the data, because of conflation of the wheel track with the rightmost extension of the bicycle and rider.
Bicyclists' proper lane position depends several factors besides the dimensions of the door zone. If traveling as fast as the motor vehicles -- either because these are traveling slowly or because the bicyclist is going fast downhill -- the bicyclist should ride in line with them (explanation). Also, before passing a long truck or bus, the bicyclist should merge several feet away from its side so as to be able to brake and drop back if it begins to merge toward the bicyclist. When passing a long stretch of empty parking spaces, the bicyclist may merge somewhat to the right to make it easier for motorists to overtake. When traveling at 5 miles per hour or less, and especially if traffic to the bicyclist's left is stopped, the bicyclist may safely stay within the door zone. So the distances I have indicated as sufficient to avoid the door zone should not be regarded as establishing fixed limits for the bicyclist's road position. They do, however, reflect typical conditions as bicyclists pass rows of parked passenger vehicles and light trucks.
The Cambridge study included questionnaires, and the answers indicate that bicyclists generally prefer the bike lane over other treatments. This result is consistent with the bicyclists' riding in the bike lane. Most bicyclists are excessively fearful of being struck from behind by a motor vehicle, and excessively unconcerned or fatalistic about the dooring hazard. However, bicyclists' preference has no bearing on whether the door zone actually is safe for riding at normal bicycle speeds. Crash statistics demonstrate that it is not.
Now let me try to take the discussion to a higher level.
Improving bicycling conditions on a street like Hampshire Street in Cambridge, the location of the test sites in this study, is not an easy matter. Hampshire Street is 44 feet wide, two-way, two-lane, with parking on both sides. If bicyclists are riding outside the door zone, motorists will have to merge partway into the oncoming travel lane to overtake safely.
As traffic volume increases, the opportunities to overtake become fewer, and bicyclists increasingly delay motorists. Then at even higher traffic volume, the motor traffic becomes congested waiting for traffic signals, and motorists delay bicyclists. Bicyclists can then filter forward slowly on the right of stopped traffic in reasonable safety as long as they do not cross gaps where they may be struck by left-turning vehicles, and do not pass the first vehicle waiting at an intersection. Under these conditions, an edge stripe or bike lane stripe becomes advantageous because it helps keep motorists farther from parked vehicles.
The freest flow of traffic is achieved through a fluid and dynamic interaction among all road users, allowing overtaking whenever it is reasonably safe. Marked lanes regularize the flow of traffic but impose a rigid compartmentalization of space, reducing this fluidity. It is illegal for a motorist to merge across the double yellow line to overtake a bicyclist who is riding outside the door zone, or to merge into an empty bike lane, away from an oncoming vehicle overtaking a bicyclist -- though in fact, both of these practices are common.
The five-foot width of a standard bike lane is intended to be at least marginally sufficient to allow one bicyclist to overtake another, after giving an audible warning. However, when only the leftmost edge of the lane is outside the door zone, then the safe overtaking location is entirely outside the bike lane. Bicyclists may, however, feel pressured to keep right in the bike lane to allow other bicyclists to overtake.
Though crash statistics show that it is preferable to stay outside the door zone, most bicyclists, as the study shows, choose to ride within it. Many if not most bicyclists and non-bicyclists alike tend to take the bike lane at face value, as the one place bicyclists should ride. The City of Cambridge has chosen to accept and formalize this situation by striping a bike lane that is mostly inside the door zone, and in this report, to rationalize the choice by pretending that much of it is not.
The report includes the sentence, on page 3:
Oddly, the report does not mention that Massachusetts law does not place the responsibility on the motorist, though Cambridge has an ordinance which does. In any case, knowledgeable bicyclists know that riding inside the door zone requires complete trust in the motorists not to open their doors, trust that can't be expected. Knowledgeable bicyclists know that they must ride outside the "door zone" also to avoid other hazards such as pedestrian walk-outs and motorists entering from side streets and driveways (explanation).
The door-zone hazard can be somewhat reduced by educating motorists, but it can be essentially eliminated only by educating bicyclists. Even if motorist education were to succeed in eliminating dooring crashes, motorists would still have to open their doors and walk on their vehicles' street side. Unless bicycle traffic is very light, so motorists can do this entirely within gaps between approaching bicyclists, bicyclists have either to wait or to merge out of the door zone. For this reason, door-zone inconvenience both to bicyclists and to motorists can be avoided only if there is sufficient width for moving motor vehicles to overtake bicyclists who ride outside the door zone.
On a street with marginal width like Hampshire street, I see only three solutions that would accommodate heavy bicycle traffic well, without causing significant delays to motorists. One would be a major reduction in motor traffic. Another would be removal of parking on one side. I'm not ready to answer how either of these would be politically achievable -- though a parking ban at high-traffic times has worked elsewhere. The third solution would be to make the street one-way, so bicyclists mostly travel only on one side. That solution would not work for Hampshire Street because there is no parallel street to carry traffic in the other direction.
Bicyclists' delaying motorists is often described as a major issue with narrow streets, but let's not forget that motorists also delay bicyclists. On a street that has been narrowed by parallel parking, parked motor vehicles reduce the street's carrying capacity and cause the delays for both bicyclists and other motorists. I have read somewhere, and I wish that I could cite the source, that the use of street width for car storage is debatable when it interferes with the main purpose of the street as public travel space. Let's not also forget that bicycle use also benefits motorists, primarily by reducing parking demand in high-density areas.
All in all, I would be much more satisfied if the City would acknowledge, rather than to dismiss and obfuscate, the problems with its door zone bike lanes. Acknowledging the problems might lead to bicycle-program improvements by turning attention to solutions that work, and to problems that admit of practical solutions.
Ever since I was a member of the Cambridge Bicycle Committee in the mid-1990s, I have been asking for a better alternative to Cambridge's use of one-way signs to keep through traffic out of the residential neighborhoods (see my parting letter to the Bicycle Committee, from 1996). These signs prevent through travel on neighborhood streets, and are more disadvantageous for bicyclists than for motorists. Cambridge has even created more such problems in recent years, with the closing off of Webster Street and the reversal of direction of the east end of Franklin and Green Streets. Other American cities -- Berkeley, Palo Alto, Seattle, Madison, Eugene for example -- use a "bicycle boulevard" approach with bicycle-permeable barriers, diverters, small traffic circles and contraflow bike lanes to reduce through motor vehicle travel on local streets, while still allowing motor vehicle access and through bicycle travel.
No nearby streets, however, parallel Hampshire Street and a couple of other main east-west arterials in Cambridge, and so any solutions must be found on these streets rather than by finding alternative routes.
Stepping back even further in the discussion, is the motivation and intent of bicycle programs to provide the best possible conditions for an existing or anticipated bicycling population, or is it to attract more people to ride bicycles, at the expense of turning a blind eye to safety issues? Cambridge's bicycle program has tilted heavily toward the promotional approach, with a number of facilities that it promotes as attractive to less skillful bicyclists, but that have practical problems which have been described in the engineering and safety literature.
Are we afraid to admit that bicyclists sometimes delay motorists, or to point out that motorists also delay bicyclists? Will we foster the excessive fear of being struck from behind, and ignore the real hazard of car-door collisions, because this misconception plays well with the uninformed public? Do we assume that motorists' convenience comes first, so we will settle for second-class bicyclist accommodation right from the start? Do we accept door-zone bike lanes rather than to point to the real -- though politically difficult -- solution of moving parking off the street?
And all in all, the proof of the pudding is in the eating. Is bicycle use increasing in Cambridge? Are crash rates decreasing? Is congestion decreasing? Crash data is collected by the police department. I assisted with bicycle traffic counts when I was a member of the Cambridge Bicycle Committee in the early- and mid-1990s, and Cambridge has continued to conduct such counts.
I still see bicycles used for transportation primarily by the same type of college and university student and recent ex-student population as 30 years ago. There are a few older adult holdovers like me, and a small but growing population of low-income people who can not afford other transportation. I have seen little movement toward bicycle use by the general population, either among children -- who would benefit most from traffic calming on the residential streets -- or among adults. Promotion of bicycling has been much more successful in several other American cities. A Cambridge city official told me twice, most recently in August of 2006, that bicycle use in the city had not increased in the more than ten years since the first bike lanes were installed. (Update as of 2007: Cambridge claims a 70% increase. I haven't seen the data on which this claim is based).
I have no information yet as to crash rates, but I can't imagine that they have declined singificantly, as nothing has occurred that would have a major effect in that direction. Data collected by the Massachusetts Executive Office of Transportation rates Cambridge as having the highest bicycle crash rate of any city or town on a population basis, but on the other hand, bicycle use in Cambridge is heayy, thanks to the high percentage of college and university students.
A "visionary" social-engineering approach which stresses encouragement while it sets aside real issues of safety and efficiency, and turns its back on scientific veracity, can fairly be criticized as "end justifies the means" politics, window dressing that exposes citizens to real hazards without their informed consent, in pursuit of what is seen as the greater good. If real improvement is not achieved, all this also is in vain.
I am concerned, in the long run, as to what will happen in Cambridge as the rising cost of motor fuel either slowly or suddenly leads more people to take up bicycling. Will the city be ready? Will the measures the city is putting in place now be seen as having prepared well, or will they be seen as mostly irrelevant? Cambridge has done certain things such as installing bicycle parking which are unquestionably beneficial for bicyclists. But has Cambridge, with its active bicycle program, actually done more to improve bicycling conditions on its streets than Boston, which has done nearly nothing at all? Time will tell.
How Pavement Markings Influence Bicycle and Motor Vehicle Positioning: A Case Study in Cambridge, MA, by Ron van Houten and Cara Seiderman
San Francisco Shared Lane Marking Study -- includes data on car-door opening widths and describes an alternative to bike lanes
A survey of car-door opening widths, which corroborates the San Francisco data.
The City of Chicago Bike Lane Design Guide, a widely-used but controversial reference for design of streets with bike lanes.
My review of The Bike Lane Design Guide. Find out why it is controversial. The design drawings shown are of a street with the same geometrics as Hampshire Street.
A survey of research into car-door collisions by the author of this page.
Examination of bike lanes and other facilities in Cambridge, Massachusetts, by the author of this page.
Hampshire Street photos and comments from two stages of the study period.
The Dana Laird fatal crash on Massachusetts Avenue.