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Vassar Street project: technical issues
document prepared by John S. Allen, March 5,
The bicycle accommodation in the proposed Vassarscape project does not reflect the state of the art in civil engineering and traffic engineering knowledge. It appears that reference has not been made to applicable standards for bicycle facilities, or to the research literature on such facilities.
Sidewalk-type facilities were first built in Europe beginning before the Second World War, when no research base existed. Research dating as far back as 1938 has shown beyond any reasonable doubt that the sidewalk-type facility has serious civil engineering, safety, operational and liability problems, and that it is far preferable for bicyclists to travel either on the roadway, or on separated paths which are entirely away from roadways. A major backlash against sidepath facilities has been occurring in Europe since the research results became widely known.
The proposed facility would be expensive to construct and expensive to revise once it is constructed.
A park-like sidewalk environment could be achieved on Vassar Street in conjunction with bicycle accommodation which reflects national design standards and avoids these problems, and which is much less expensive to construct. The money which would be saved could then be turned toward projects which have a positive, rather than negative, effect on bicyclists' mobility and safety.
Elevated risk of accidents on sidewalk-type facilities
Sidepaths have a higher rate of bicycle-motor vehicle collisions than streets have. This may seem surprising at first to people who have are not familiar with accident studies. However, the overwhelming majority of car-bicycle collisions-- approximately 90% -- involve turning and crossing movements. Sidepaths complicate these movements by placing the bicyclist and motorist out of sight of each other and on conflicting paths at junctions (The term "junctions" as used in the research literature refers not only intersections with streets, but also places where driveways cross the sidewalk.)
Bicycle accidents which do not involve motor vehicles are rarely reported to police. However, as shown in all studies which are population-based, bicycle/motor vehicle collisions are only 10% to 20% of injury-producing bicycle crashes. The comparison between sidepaths and roads for crashes which do not involve motor vehicles is extremely unfavorable to sidepaths. In particular, the more restrictive geometrics of sidepaths lead to more single-bike crashes; also, bicyclists can not travel safely at normal speeds in the presence of pedestrians, because pedestrians suddenly and unpredictably change direction. A collision between a bicyclist and a pedestrian is as likely to injure the pedestrian as the bicyclist, and so pedestrian injury rates also increase greatly from the placing of bicycles on sidewalks.
The false belief that car-overtaking-bicycle collisions are the predominant car-bicycle collision type is in large part responsible for the disproportionate fear of that type of collisions, and the false idea that placing biyclists on sidewalks will increase safety. As first demonstrated in the Cross and Fisher study conducted in the 1970s, and as confirmed for the Boston area in the 1984 Metropolitan Area Planning Commission study posted on my Web site, only a small percentage of car-bicycle collisions on roadways is overtaking collisions.
Would any traffic engineer design a divided highway, with two-way traffic on each of three parallel roadways? That is what is proposed here. The problem of conflicts at junctions with sidepaths can be reduced only by measures that substantially slow or delay bicyclists, motorists or both. Even the most advanced measures of this type do not succeed in reducing the crash rate to that for riding on streets.
Evidence from the research literature
The evidence that bicycling on sidewalks and similar facilities is more hazardous than bicycling on streets is overwhelming.
A survey of research on the accident rates of streets, bicycle paths and sidewalks is available on the Internet at http://www.lesberries.co.uk/cycling/cy_pathr.htm. And here are some links to specific studies posted on the Internet:
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 two studies are are privately posted in connection with this document, as I do not have reprint rights:
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).
German bicyclist Berndt Sluka has surveyed the results from several European studies; see my translation of his Web page.
Europe has many more sidewalk-type facilities than the U.S., having gotten into the habit of building them before there were research results to warn against them. A strong backlash against them has occurred in Europe in recent years. A press release by the German Bicycle Federation ADFC (the national German bicyclists' organization) gives an example of the tone of the discussion occurring at present. An ADFC report on a conference held in Austria in 1990 includes additional data on crash rates for sidepaths.
Civil engineering issues
Much of the proposed sidepath is adjacent to tree plantings. The roots of the trees will heave up the pavement as they grow. This problem is especially serious because trees will find water more abundant beyond the sidepath than on the street side.
Root damage is an endemic problem on bicycle paths but only rarely a problem in streets. That is because streets are wide enough to shield the soil beneath them from water percolation, and are bordered by deep curbstones which serve as root barriers.
Pedestrians can tolerate pavement heaved up by roots, but for bicyclists it is a serious hazard. A root across the bicyclist's line of travel causes a jolt and possible loss of control. A root that is more nearly parallel to the bicyclist's line of travel can sweep the bicyclist's front wheel to the side, causing a "diversion-type fall" which typically results in injury to the hip, shoulder or head.
An example of root damage on a bicycle path is shown in the photographs below.
Root damage on Paul Dudley White bicycle path near MIT's Pierce Boathouse
Streets are crowned to facilitate water runoff, and are provided with storm grates, catchbasins and storm sewers. The plans for the project indicate no drainage provisions for the sidepath segments other than for rainwater to run off into the street. Even if the path is sloped to facilitate drainage toward the street, puddling will occur increasingly over the years as the soil settles and as roots heave up the path. When plowed snow blocks drainage to the street, drainage will be completely blocked over long segments of the path.
Snow and ice.
Snow removal from a sidewalk is never a successful as from a street. On a street, motor vehicle tires wear away snow, and quickly open up patches of pavement, which facilitate heating by sunlight to complete the melting.
In addition, a more aggressive use of snow-melting chemicals is practical on streets, where they are carried away in the storm drain system and do not pose a substantial risk of damage to roadside vegetation.
Particularly when drainage is blocked by plowed snow and by heaving up due to tree roots, puddles on the path refreeze into ice, making the path unsafe for bicycle travel. Ice puddles are a very minor problem in a street, because it is crowned and because of its drainage provisions.
Plowed snow from the driveways will block the path until cleared from the path. No such problem occurs with streets.
All in all: Pedestrians can tolerate imperfect snow clearance, and can even beat a path for themselves where there is no snow clearance. Bicyclists cannot. After a snowfall, sidepaths remain unusable, and then unsafe, for bicycle travel far longer than streets.
Inevitability of two-way bicycle travel on Vassar Street sidepaths
The sidepaths have been designed based on the faulty assumption that they will carry only one-way traffic on each side of the street. This assumption is highly unrealistic because, with paths behind curbs, it is inconvenient to cross the street to enter the path on the other side.
Easy crossing can be accomplished only where there is a curb cut or driveway. Getting to the nearest entry point for the opposite sidepath requires either riding away from the intended destination and then making a U-turn, or riding the wrong way on the sidepath -- the more likely choice. Many of the entry points for the two sides are not opposite one another, and so it will often be necessary to lift the bicycle over a curb and sometimes, thread the bicycle between parked cars -- or else ride along the narrowed street -- the more likely choice, to get from one sidepath to the other.
Crossing to a street-level bike lane or the opposite travel lane of a normal street poses no such problems.
Most trip generators on Vassar Street to the east of Massachusetts Avenue are on the south side, and so use of the south sidepath will be heavy in both directions, and use of the north sidepath will be light. The opposite is the case west of Massachusetts Avenue and will be more so following completion of the Simmons Dormitory, now under construction.
Where the sidepath transitions to a bike lane as it approaches the intersection with Massachusetts Avenue or Main Street, bicyclists who are riding opposite the traffic flow in the sidepath will most likely continue on the sidewalk, rather than to approach the intersection traveling opposite traffic in the bike lane. They will be subject to the very high risk associated with crossing intersections on the left crosswalk, as described in the studies cited above.
Are pedestrians separated from bicyclists?
The proposed sidepaths connect with one-way bicycle lanes at Massachusetts Avenue and Main Street, and are unrealistically intended for one-way bicycle travel.The sidepaths are to be 5 feet wide, and separated from pedestrian traffic on the adjoining 8 foot sidewalks by a painted stripe 1 foot wide.
5 feet does not meet the current AASHTO standards for width of even a one-way bicycle path. When one bicyclist is overtaking another traveling in the intended direction, the tendency will be for the slower bicyclist to remain in the bikeway, while the faster bicyclist merges to the right -- not to the left as with normal overtaking -- and into the sidewalk area. This confusion puts both of the bicyclists at risk, as well as pedestrians.
A very confusing situation will occur when a "wrong-way" and "right-way" bicyclist approach one another. One or the other bicyclist will have to merge into the area designated for pedestrians. Which bicyclist? The "right-way" bicyclist may feel justified in keeping a straight course on the designated bikeway, but then the "wrong-way" bicyclist will have to pass to the right of the "right-way" bicyclist, contrary to the usual traffic rules. Suppose that the "right-way" bicyclist yields to the right as is normal, and the "wrong-way" bicyclist yields to the left, assuming that the "right-way" bicyclist will stay in the designated bikeway? Then they collide head-on. Confusions become far more complicated when bicycle and pedestrian traffic is heavy, and they lead to bicycle-pedestrian collisions as well as bicycle-bicycle-collisions.
By way of comparison, the standard overtaking rules on the roadway are simple and clear: slower traffic keeps right and faster traffic overtakes on the left after looking back to check that there is not another vehicle (bicycle or motor vehicle) already overtaking.
Confused yielding rules, sight obstructions
On the street, through traffic has the right of way over turning traffic. On the sidepath, because of sight line problems, both through bicycle traffic and crossing motor traffic must slow and be prepared to yield, since neither the bicyclist nor the motorist can be sure to see the other in time. The problem occurs because the bicyclist is hidden behind parked cars, or in the right rear blind spot of a motor vehicle which has slowed to turn. It is typical in this situation to install stop signs for the path as well as the road. The example below is from the Route 28 bicycle path in Hyannis. Bicyclists on the path must yield at the stop sign, and turning vehicles must yield at the crosswalk marking.
Sight obstruction by tree, bicyclist in camera position
would be in motorist's
right rear blind spot; also right-of-way confusion, Route 28 bike path, Hyannis.
Blocking of street by vehicles backed up to exit driveways, and blocking of path by vehicles backed up to enter driveways.
Placing multiple two-way rights of ways adjacent to one another creates crossing and turning conflicts like the one illustrated below. To yield to traffic in the roadway, the motorist must block the bikeway. To yield to traffic in the bikeway, the motorist must block the roadway. The standard traffic pattern, with slower traffic on the right and faster traffic in the middle, avoids this problem.
On streets, bicyclists can usually safely travel at the speed their legs can propel them, except when required to yield at intersections or under congested conditions. On a sidepath, every driveway and cross street becomes an intersection and bicyclists must slow or stop much more often. The sidepath promotes a false sense of security and bicyclists often do not use appropriate caution.
Car blocking path, Route 28 bike path, Hyannis
Bicyclists will still use the street.
Most of Vassar Street presently has ample width for bicycle/motor vehicle lane sharing. The project proposes to eliminate this, reducing travel lane width to 11 feet. However, the project will not eliminate the need or desire of bicyclists to ride in the roadway, for several reasons, some already stated
The only part of Vassar Street where lane sharing width is presently an issue is the part which currently has angle parking. In this part, the eastbound lane is narrowed to allow more room for vehicles to back out of the angle parking spaces on the far side of the street. However, the angle parking has a low turnover rate and motorists have no problem overtaking bicyclists.
Adult riders do not belong on sidewalks
The MIT campus is separated from other areas of Cambridge by the Grand Trunk railroad line. Almost all bicyclists using the Vassar Street corridor are affiliated with MIT and are young adults who are generally in good physical condition and riding efficient, multi-geared bicycles, with typical cruising speeds between 15 and 25 miles per hour. These speeds are unsafe on the proposed facility, and are appropriate for street travel, not for sidewalk travel. MIT students also are sufficiently mature and intelligent to operate a bicycle according to the rules of the road.
Walking a bicycle in order to avoid challenging traffic conditions is sometimes appropriate for children and novice bicyclists. However, it is much slower than riding, and adults do not put up with it except under unusually difficult conditions. Traffic on Vassar Street is relatively light, and all of its intersections with streets are controlled by traffic signals.
The proposed pedestrian-type facilities are a hindrance rather than an aid to bicyclists who expect to be able to get to their destinations quickly, and create a chaotic, disorganized traffic pattern and increased risk of accidents. Without the proposed sidepaths, bicyclists still have the option to ride slowly on sidewalks and cross intersections as pedestrians if they wish to do so.
Arguments that are made for sidepaths and why they do not apply here:
Sidepaths make sense where traffic conditions are extreme and there is no cross traffic: for example on a highway bridge with high-speed traffic, narrow lanes and no shoulders. That is not the case here.
The two most common arguments that have been made for sidepaths are that they are safer, which is false except under unusual conditions, and that people think they are safer. The latter argument, sometimes naively and sometimes not, frequently becomes a basis for political action, on grounds that people should be encouraged to abandon motorized transportation for bicycling and walking. But when the facilities constructed make bicycling more dangerous and slower, this amounts to shooting oneself in the foot on the encouragement issue, and is unethical.
In any case, such encouragement is irrelevant at MIT. Short distances, and an extreme shortage of parking spaces, assure that even people who drive to campus park their car for the day. The Vassar Streetscape project, as proposed, would make both walking and bicycling more hazardous, and would make bicycling slower, but would do nothing to effect a modal shift away from motor vehicles toward non-motorized modes.
MIT exposes itself to a serious liability risk if it funds the construction of the proposed sidepaths, as described in the paper Liability Aspects of Bicycle Environments: Bicycle Facilities and Roads, by three notable experts on bicycle transportation, Alex Sorton, P.E,.Tom Walsh, P.E and John Williams. This paper was presented at the Institute of Traffic Engineers 1990 Annual Meeting. The complete paper is included with this document for reference (but not for reprinting; I do not have reprint rights) [Not included with version published on the Web due to copyright issues]. Here are extracts:
What the AASHTO bicycle facilities guide says about sidewalk vs. on-road accommodation of bicycles
[The 1999 AASHTO Guide for the Development of Bicycle Facilities is available online and also from the AASHTO bookstore: Print version; CD-ROM version. I have published a critique of the Guide's recommendations on sidewalk and sidewalk riding on another Web page. The quotes on that page convey the intent of the Guide. In this public posting of the Vassar Street critique, I am omitting lengthy quotes from the AASHTO Guide which would infringe on AASHTO's copyright. Rather, I am indicating only the beginnings and endings of the sections I quoted, so readers may look them up in the Guide. I suggest opening up the online version in a separate window to read the sections to which I refer below.
Violations of the guidelines in the Vassar Street project are indicated in red; other sections, for reference, are in black. The longer version delivered to the project planners included several illustrations from the Guide.]
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