Bike blogger Elly Blue, from Portland, visited Seattle recently and came away startled by how many streets were marked by sharrows---pavement markings to let cyclists and drivers know they should share the lane. Sharrows are controversial among bike-safety advocates, who say they're inferior to bike lanes and separated bike facilities; give politicians a pass on funding real bike infrastructure; give cyclists a false sense of security; and, when placed too indiscriminately, become easy for drivers to ignore.

Here's Blue, in Grist:
Seattle has its own brand of sharrow growing pains. Riding and walking around town, it's hard to see a logic to the streets chosen for sharrow treatment. Some are on relatively quiet back streets, others are on breathtakingly fast arterials where the symbols are worn and rutted by the daily flow of cars and trucks speeding over them.

Sharrows are popular because they are politically easy -- you can almost hear city officials sigh with relief when sharrows are mentioned. On the surface, they seem like a way to please the increasingly vocal bike lobby without ruffling feathers by putting in a bike lane at the expense of car parking or traffic lanes, which are often perceived as being for cars only. And they're cheap: Sharrows cost only $229 each to install, including labor and materials, while a full-blown bike lane can cost between $5,000 and $60,000 per mile.

But do sharrows work? One recent study says sharrows slow car traffic slightly, and make bicyclists a little safer. But they are even better at keeping drivers at a distance from parked cars -- once again, bike infrastructure benefits more than just people on bikes.

In Portland, Blue reports, sharrows have been added to the street grid in a less haphazard manner, with bike planners focusing on low-traffic neighborhood streets where cars are less likely to be already.