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The Bike Lane Design Guide --

"Honey, they shrunk the cars!"

by John S. Allen

(In case you, my reader, aren't versed in American popular culture, the line in quotes above refers to the title of a Disney movie.) Now, back to the serious discussion.

The Bike Lane Design Guide, published by the Pedestrian and Bicycle Information Center of the University of North Carolina in cooperation with the Chicagoland Bicycle Federation and the City of Chicago, recommends dimensions for installation of bike lanes on urban streets.

Each page of plans in the Bike Lane Design Guide is formatted to look like a dimensioned engineering drawing, and stamped with the seal of the City of Chicago.

Version #1of the image that appears below (numbered in upper left corner) is as it appears on page 7 of the Bike Lane Design Guide. The four other versions have been modified by the author of this page. Click through them and try to figure  out what they tell you. Scroll down when done to see my answers below the image.

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Sequence of traffic movements (Javascript-enabled images)

  • Image #1, with the narrow vehicles, is from the Bike Lane Design Guide.

  • Image #2 is modified to show the width of real vehicles.

  • Image #3 shows these vehicles with their driver's side doors open.

  • Image #4 shows safe lines of travel for bicyclists passing vehicles whose doors might open quickly, and for a motor vehicle overtaking one of these bicyclists.

  • Image #5 shows one example of thinking outside the box, converting the street to one-way.

Here are some issues highlighted by the comparison:

  • The widths of motor vehicles shown in the Bike Lane Design Guide are approximately 80 percent of the widths of representative real vehicles. The real and typical vehicles whose measurements were used for the comparison images have widths between 68 and 76 inches.

  • The explicit dimensioning of lane widths increases the deceptiveness of the drawings by implying that everything in them is to scale, including the widths of the vehicles.

  • The Bike Lane Design Guide's recommended dimensions do not addresses the issue of a driver's side door's opening into the bike lane, though "doorings" constitute a very substantial percentage of serious crashes for bicyclists on streets with parallel parking -- see discussion on another Web page. Vehicles may also pull out of parking spaces unexpectedly, and pedestrians may walk out from concealment in front of vehicles.

  • The centered placement of the bicycle symbol and arrow in the lane, and the edge stripe on both sides, suggest that riding anywhere in the lane is equally satisfactory. Due to the problems just described, that is not so. Only the very leftmost edge of bike lanes dimensioned as shown is safely rideable at a speed much above 5 miles per hour. Some bike lanes lack the right stripe and do not convey the false impression: example. The shared-lane marking is another useful alternative, even on streets with inadequate space for motorists to overtake bicyclists in the right lane.

  • When riding fast, bicyclists need to ride farther from parked vehicles to see and be seen in time by pedestrians and by drivers in side streets and driveways. On downhills where bicyclists travel as fast as motorists, the required sight distances increase, and bicyclists must ride in line with the other traffic -- completely outside the bike lane markings -- to see and be seen early enough. Like all other drivers, bicyclists should overtake slower traffic on the left. Overtaking on the right in the bike lane risks being struck by a vehicle that is preparing a right turn. (Chicago is very flat; many other cities are hilly. Residents of such cities have suggested that bike lanes are inappropriate on steep downgrades, and I agree.)

  • Only one of the vehicles in the Bike Lane Design Guide is shown with side mirrors. Vehicles in the modified images show side mirrors, because real motor vehicles have them. Protruding side mirrors are generally at the same height as a bicyclist's waist and handlebars and can convert a sideswipe into a serious impact.

  • In the Bike Lane Design Guide, motor vehicles are shown parked 8 to 12 inches from the curb. In reality, they often are not parked as close. In Massachusetts, for example, it is legal to park as much as 18 inches from the curb. Distance from the curb has, however, not been altered in the modified drawings.

  • Two-way bicycle and motor traffic on a 44-foot wide street with parking on both sides does not allow safe clearances unless motorists cross the centerline to overtake. If traffic is heavy, overtaking opportunities are limited for bicyclists and motorists alike. An alert oncoming motorist could merge slightly right, into the bike lane to make room if no bicyclist is present, though driving in the bike lane is illegal -- one argument against bike lanes. A one-way street allows much more freedom in choosing lane widths. Page 15 of the Bike Lane Design Guide gives one example of a one-way street -- 48 feet wide -- but this page shows the bicyclist riding within range of opening car doors. Most of the width that is freed up is wasted in a very wide left travel lane. Example #5 in the series above allows free overtaking by motorists; bicyclists must leave the bike lane to overtake safely, though.

  • Often -- indeed usually -- simply converting part of a street to a bike lane doesn't work out. Looking at the problem on a larger scale is very desirable. Converting adjacent, parallel streets into a one-way pair, as in image #5, or perhaps some other solution entirely, may be better. Experience and discretion are of paramount importance in seeking and implementing such solutions. Image #5 shows both bicyclists and motorists overtaking safely.

  • All in all, the Bike Lane Design Guide gives a highly deceptive impression of the design of a bike lane in which bicyclists may ride safely clear of parked motor vehicles. The deceptive, narrow vehicles are shown in every one of the 35 design drawings in the Bike Lane Design Guide, not only the one on Page 7.

There is heated controversy in the bicycling community about bike lanes. Many advocates of transportation reform seize upon bike lanes as a simple, seemingly logical way to increase the appeal of bicycling. These people tend to regard the use of road space as a political turf battle between bicyclists and motorists, and to use expressions such as "making space for bicyclists". On the other hand, people who have explored  issues of safety, mobility and political unintended consequences disparage bike lanes where the highest safe travel speed is 5 miles per hour, which attract inexperienced, trusting bicyclists into hazardous situations, and which lead the non-bicycling majority of the public to become annoyed with bicyclists who refuse what they perceive as a special privilege. This is a classic example of a controversy between people who believe that the ends justify the means, on the one hand, and people who value the rights and safety of the individual, on the other.

The controversy often goes overboard into a stark "bike lanes vs. no bike lanes" dispute, and that is unfortunate because bike lanes can be appropriate and useful -- but only if certain conditions are met. One important condition is that a bike lane must allow bicyclists to travel safely at their normal speed of 10 to 25 miles per hour. (Some good examples -- and bad ones too -- are shown here and here.)

The bike lanes adjacent to parallel parking shown in the Bike Lane Design Guide do not pass. The Bike Lane Design Guide is harmful in suggesting inappropriate bike lane designs, and so in turning attention away from other measures which are effective and safe. In using deceptive illustrations labeled as dimensioned engineering drawings, the Bike Lane Design Guide certainly does nothing to enhance the credibility of the organizations that produced it.

The vehicles used as models in the comparison drawings are
  • Upper left: 1997 Ford Taurus station wagon, four-door: width 73 inches, driver's side door protrusion 37 inches.

  • Lower left: 1995 Ford F250 pickup truck: width 76 inches, door protrusion 37 inches -- typical of full-size pickup trucks and SUVs.

  • All cars parked at the right and in motion: Typical mid-sized two-door sedans. Width 68 inches, door protrusion 44 inches.

Some passenger vehicles, particularly older, larger two-door cars, are wider than those shown -- as wide as 80 inches and with a 44-inch door protrusion.   Bicyclists must merge slightly farther left than shown in the fourth illustration to clear these safely -- and even farther left to clear large trucks and buses safely.

A graph showing the width of representative parallel-parked vehicles to the limit of the driver's side door when open is available on another Web page prepared by the author of this one.


The Bike Lane Design Guide, posted on the Web site of the Pedestrian and Bicycle Information Center.

John Forester's discussion of the Chicago Bike lane Guide (scroll down to section 3).

Two papers, Bicycling and On-Street Parallel Parking and AASHTO and Door Zone Bike Lanes, by Wayne Pein.

Chicagoland Bicycle Federation newsletter claiming increase in bicycle use and decrease in crashes, and attributing these to the installation of bike lanes.

Examination of bike lanes and other facilities in Cambridge, Massachusetts, by the author of this page.

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