In the late 1990s, bicycle lanes were painted on streets in northwest Portland, a high-density neighborhood less than a mile from downtown. But congestion at traffic lights made reducing space for automobiles impractical in some areas. As a result, the project left a nine-block gap in the bike network.
Caught between the need for a continuous bike lane and the demands of drivers, Portland transportation engineers finally came up with a solution. Next month, the city will fill the gaps in the network with new shared-lane pavement markings, called "sharrows." Stencils of a bicycle with two chevron markings above it will be painted, two per block, in areas too narrow for a bike lane. The idea is to keep cyclists away from parked cars while promoting awareness of their right to use the road.
"The sharrow sends the message to cyclists, 'yes, you are welcome here,' " says Mia Birk, a principal with Alta Planning + Design in Portland and lead author of a recent study on shared-pavement markings in San Francisco.
Pioneered in Denver in the mid-1990s, sharrows are attracting the attention of transportation officials around the United States. But the markings are controversial. In June, Boulder, Colo., became one of the few cities outside of California to install the shared-lane markings; that same month, sharrows were rejected by the National Committee on Uniform Traffic Devices, an organization that sets national traffic standards.
"We have a litigious society," says Ms. Birk, explaining the challenges of implementing bike-friendly street designs. "It takes a progressive traffic engineer to say 'I'm comfortable enough to take a risk.' "
Some cycling advocates say sharrows will preempt the installation of bike lanes, which often entail hard-fought battles to remove a car travel lane or on-street parking.
"Once sharrows are accepted, they will become the preferred solution," says Kevin Jackson, who sits on the Bike and Pedestrian Committee in Sunnyvale, Calif. "Not because they are better, but because they are politically expedient."
The principle behind sharrows is simple: They reinforce existing rules of the road. In most states, cyclists are required to stay as far to the right as possible, except under unsafe conditions. One of these conditions is when the travel lane is too narrow for side-by-side passage of an automobile and a bicycle.
"The most dangerous place for a cyclist to be in a narrow travel lane is far to the right, because you are in a 'door zone' and motorists think they have enough room to stay in their travel lane and pass you," says Roger Geller, Portland's bike coordinator. "Every cyclist who has stayed right on a road has had the experience of a car passing 25 miles an hour within six inches of his left elbow. At the same time, should someone [in a parked vehicle] open the car door, you're right there."
Portland decided to experiment with sharrows, Mr. Geller says, after the Alta study found the marking provided a statistically significant benefit to cyclists by encouraging them to move left and center. The study was commissioned last year in an effort to improve cycling conditions on San Francisco's crowded streets. Since then, the California Traffic Control Device Committee, an advisory body, has recommended that the marking be adopted by the entire state. Over the past six months, San Francisco has stenciled 500 sharrow markings on city streets and by the end of the year will have 2,500.
"Cyclists are very positive about the marking," says Mike Sallaberry, San Francisco's bike facilities engineer. "They like the fact that something positions [them] in the road." The city has also embarked on a campaign to educate cyclists and drivers about the markings, he says.
Oregon's automotive advocates also support the sharrows concept. As gas prices rise, more people will ride bikes, notes Elliott Eki, public affairs director for AAA Oregon. "If sharrows are well placed," he says, "they will help cars and bikes share the road more safely."
Shared-lane markings have gained acceptance in some European and Australian cities. An Australian report published several years ago on "bicycle friendly zones" - the sharrow equivalent - suggested that shared-lane markings can be more effective than bike lanes in encouraging cyclists and motorists to pay attention to one another. The report also says the markings slow traffic and encourage all modes to share limited street space.
Sharrow opponents say the more important issue is removing on-street parking to create room for bike lanes. "What you need is bicycle space," says Mr. Jackson, noting that activists recently persuaded the city of Sunnyvale to switch from sharrows to a bike lane on one major road.
Geller himself questions the value of sharrows for beginning cyclists. "Cyclists who ride in the center are typically the strong and the brave," he says.