Shared lanes with painted Sharrow symbols are not a bike facility. They’re an admission that this is a good route for bikes, but a proper safe bike facility is missing. They do not provide safe space to ride a bike, nor do they encourage anybody to ride a bike. But there's another problem, even a wide shared lane isn't really all that good. Is it time to scrap the wide shared lane entirely?
The Sharrow markings are often used in two ways, in a “wide” lane off to the side, or in the centre of a narrow lane. You would think the wide lane is the better option providing enough space for vehicles and cyclist to share the same lane, but the reality is that most implementations of the shared lane adopt the minimum width of 4.3m. Any more would simply increase cost. I’m not sure where the 4.3m width came from, but the problem is 4.3m is not enough for a vehicle to give the cyclist sufficient space when passing. It may be a leftover from legacy guidleines that didn't give much consideration to cyclists.
My experience of shared lanes, both as a cyclists and as a driver are uncomfortably tight on many occasions. As a cyclist you most definitely feel threatened. For some reason many drivers don’t like to change lane when passing, perhaps because there is traffic in an adjacent lane, but often even when there is not. Unless you’ve experienced it first hand you’ve likely never applied any critical thinking to the guidelines. I have and I don’t recommend 4.3m shared lanes.
There is no precise guidance on the position of the Sharrow in a shared lane, but lets assume it’s positioned in the centre of an imaginary 1.5m bicycle lane, i.e., the tip of the arrow is 0.75m from the gutter, and the cyclist is expected to cycle in line with this. If the car stays in the lane, the gap between elbows and wing mirrors is just 0.7m, nowhere near enough to feel comfortable for the person on the bike.
Even if that person is to ride as close to the gutter as possible, which isn’t really reasonable, and the car is still at the edge of the lane, the gap between elbow and wing mirror is about 1.15m, better, but not ideal. 1.5m is generally acknowledged as a more comfortable gap these days.
If we look at what a 1.5m gap looks like with the cyclist in a reasonable position over the top of the Sharrow. The car must leave the lane to pass safely.
The upper limit for a shared lane is 4.9m. What does that look like with the cyclist still riding in line with the Sharrow and the car 1.5m away? Its pretty close to acceptable.
4.9m is cited as the practical upper limit for a shared lane, but 4.9m would provide enough space for a 1.5m bike lane and 3.4m vehicle lane. While a 1.5m bike lane is at the lower end of the spectrum today, its better than no bike lane. The 3.4m vehicle lane is more than wide enough for most urban streets, even if they carry large vehicles such as trucks or buses.
Looking at a more conventional lane, 3.5m has long been a normal lane width in urban areas. By today’s standards its a little wide and unnecessary, only encouraging drivers to drive at higher speeds. But in this circumstance, giving the cyclist the right to use the full lane means putting the sharrow in the middle. If a driver is following a cyclist, they must change lanes to make a safe pass.
In conclusion, there is no real role in the world for a wide shared lane. If you have a lane wide enough for a comfortable shared lane, its actually wide enough for something better. If you have enough space for a 4.3m wide shared lane, you’d probably be better off reducing the lane width to somewhere between 3m and 3.3m, making it a single file shared lane, and using that extra metre or so for something else.
And the very final word... For any drivers reading this... change lanes to pass!