Six degrees of separation is the idea that all living things and everything else in the world are six or fewer steps away from each other. That has absolutely nothing to do with this but it makes for a good title! There are many ways to design an intersection to accommodate pedestrians, cyclists and vehicles. There are certainly more than six configurations of protected intersection, but those shown below, may constitute the most common types. What kind of facility would you feel safest riding through?
Option One is the unseparated intersection, cyclists are brought back on-street at the intersection. This reduces conflicts between pedestrians and cyclists, however, it puts cyclists, potentially less confident, young, or old cyclists, back in close proximity to vehicles, reducing their sense of safety and potentially discouraging cycling when compared with the other options. This design can work with reduce buffers on either side of the bike path and potentially no buffer between the bike path and sidewalk. As cyclists are forced back on-street to somewhat mix with traffic, it cannot be considered a truly all ages and abilities facility.
Option Two brings cyclists and pedestrians together at the intersection in a shared mixing area. This is easy to design, but there is no clear right-of-way, thus there is greater conflict, and this design is reliant on pedestrians and cyclists to be aware, make eye contact with each other, and generally be courteous to their fellow humans. As the pedestrians and cyclists share the same area, this design can also work in constrained spaces as it does not require any separation between sidewalk and bike path.
Option Three sees different areas marked out for pedestrians and cyclists by surface treatment, typically with the cyclist areas using asphalt, and the pedestrian areas in concrete. This helps delineate the space where each should be, and zebra crossing markings across the bike path clearly indicate that the cyclist must yield to the pedestrian crossing.
Like Option Two, Option Three can be implemented with or without the buffer between pedestrians and cyclists if space is constrained, This is shown in Option Four below.
Option Five uses essentially the same layout as Option Three but better delineates the pedestrian and cyclist areas with changes in grade. This option does typically require a buffer between the pedestrians and cyclists to create space for sidewalk letdowns, whilst maintaining a level sidewalk around the corner.
Option Six is a refinement of Option Five, it reduces the corner curb radii from 6m to 3m to create more space for cyclists and slow down turning vehicles. It is important to maintain functionality for traffic, such tight radii may force larger vehicles to cross into the oncoming lane to make the turn. This may be acceptable on local streets with low volumes and speeds. It may also work well if there are two receiving lanes downstream of the corner. The corner protection island is reduced in area also, to create more waiting space in the corner to better manage larger cyclists volumes and allow left turning cyclists to wait out of the path of through cyclists.
Ideally when selecting a suitable configuration you would start with Option Six and work backwards until you can fit the design within the available right-of-way. Dimensions vary with the need for buffers and ability to use narrower widths of bike path and sidewalk. The table below indicates a practical range between 4.1m and 8.5m. It will be difficult to go lower without essentially combining the bike path and sidewalk into a multi-use path. It is of course possible to go higher if space and funds are available, and demand is sufficiently high to require the extra space.