They are all over the streets where I live, in Toronto, where the City says "these pavement markings are an excellent way of encouraging cyclists and motorists to share the road safely." Or not. Angie Schmitt of Streetsblog calls them " dregs of bike infrastructure — the scraps cities hand out when they can’t muster the will to implement exclusive space for bicycling." She also points to a new study that shows that they don't do much of anything.
A study by University of Colorado Denver researchers Nick Ferenchak and Wesley Marshall examined safety outcomes for areas in Chicago that received bike lanes, sharrows, and no bicycling street treatments at all. The results suggest that bike lanes encourage more people to bike and make biking safer, while sharrows don’t do much of either. They found that bike commute rates more than doubled in areas with new bike lanes, compared to a 27 percent increase in areas with new sharrows and a 43 percent increase in areas where nothing changed.
Furthermore, where bike lanes were installed, injuries decreased 42 percent; in the sharrows vs areas with no changes, the difference was not statistically significant. Angie notes that in the Netherlands, sharrows are sometimes used when roads are shared, but only on streets with a maximum speed of 30 Km/hr (20 MPH)- "mixing modes with higher speeds is deemed too unsafe and thus unethical." She quotes bike engineer Dick Van Deen:
So are sharrows bad? Not always. Using sharrows to accentuate the position of cyclists on the road can be recommendable, especially when the main culture is still car dominated. But using sharrows on a wide, high-speed route is not advisable. It is not making anything safer or easier. So if you use sharrows, be sure to include a road diet, lower the speed limit and make overtaking difficult. Than you create a bike space where car drivers must learn to behave like guests.
The way I have seen sharrows used, and the way they are explained in this video, they seem to me little more than a waste of good paint.