This is Central City Mobility Project update #25.

I have been getting questions from several people about how the turn wedges being installed as part of the Central City Mobility Project are supposed to work. In particular, this applies to all of the concrete wedges, which are at the intersection of the separated bikeways, but applies most of the other wedges as well.

First, the diagram from the Central City Mobility Project design document. This is turn wedge style 3, with concrete turn wedge. The other four styles have speed bumps and vertical delineators.

Second, a photo of an actual concrete wedge in place.

The issue that has been pointed out by more than one reader is that a motor vehicle driver can also cut between the turn wedge and the curb, to the left of the turn wedge, rather than to the right, as was intended by the design. Wow! That is a flaw. How did this happen?

Well, the city has designed partially rather than fully protected intersections. Not only are these protections only on one corner, but they are not designed according to NACTO (National Organization of City Transportation Offices) guidance. Here is the NACTO diagram, from the Protected Intersections page.

What is different? Look at the approach from the left side of the diagram. There is a concrete island, labeled 3, which prevents motor vehicle drivers from cutting through between the turn wedge (‘corner island’ is the NACTO term) and the curb. It is likely that the area labeled 1 would also be a concrete island. This island not only protects bicyclists, but more importantly, protects walkers and shortens the crossing distance. I will include text from the NACTO page below, because the details are really important.

So, how to fix the Sacramento problem? Concrete islands need to be installed in the upstream direction, before the crosswalk. In the case of the photo above, this would be where the photographer is standing. Without such protection, this cannot be considered in any way a protected intersection or separated bikeway (protected bikeway). The radius of the turn wedge is also much greater than the NACTO recommendation, 30 feet rather than less than 18 feet (see second bullet below). So we are back to ‘turn wedges of death‘. I have to say, this is typical of the city, to take a good idea and sort of implement it.

Thank you to the reader who pointed out this design flaw, and caused me to look more closely, and think more closely.

Here is the NACTO text detail, in case you don’t want to look at the page, though I highly recommend you look at all the NACTO bikeway design pages, from their new publication, Don’t Give Up at the Intersection.

1. No Stopping / No Standing Zone: Motor vehicle parking and stopping are prohibited on the approach to the intersection.
2. Bike Yield Line (optional)
3. Pedestrian Islands: Islands reduce crossing distances and improve visibility by keeping the intersection clear. Wider islands support high volumes of people walking and biking, raising the capacity of the intersection. In some cases, islands can reduce the signal time needed for pedestrians.
4. Bike Queue Area: People biking can wait ahead of the crosswalk for a green signal or a gap in traffic. This shortens crossing distances, and accommodates the natural positioning of people biking. Bike detection optional.
5. Bikeway Setback: The setback determines how much room will be available for drivers to wait and yield, and the angle at which they cross the bikeway. Larger setbacks provide better visibility and give people bicycling more time to notice and react to turning vehicles.
6. Corner Island: A corner island separates bikes from motor vehicles, prevents motor vehicles from encroaching on the bikeway, and creates a protected queuing area for people on bikes waiting to turn.
7. Motorist Waiting Zone: The space between the motor vehicle lane and the crossbike provides a place for motor vehicle drivers to wait before turning across the bike’s path of travel.
8. Crossbikes / Intersection Crossing Markings: Markings provide conspicuity and directional guidance to bikes in the intersection. They are marked with dotted bicycle lane line extensions and may be supplemented with green color or bike symbols between these lines.

And, the implementation guideance:

• Bikeway Setback: The bikeway setback distance determines most other dimensions of the protected intersection. A 10’ setback, created in the shadow of the parking/loading lane, is shown. Where practical, a setback of 14-20’ is preferred. If setbacks smaller than 12’ are used, they should be accompanied by longer clear distances, and additional signal phasing or speed reduction strategies should be considered. Setbacks larger than 20’ may increase turn speeds, and setbacks larger than 25’ should be treated as a separate intersection.
• Corner Island: Radii should be small enough that passenger cars are discouraged from turning faster than 10 mph. This is accomplished with an effective turn radius of less than 18’, usually resulting from a 10’ to 15’ curb radius. Corner islands may have a mountable override area to accommodate large vehicles. Corner islands may also be implemented as channelization markings that are reinforced by mountable vertical elements such as modular speed bumps.
• Pedestrian Islands: Wider islands support high volumes of people walking and biking, raising the person-capacity of the intersection. To serve as an accessible waiting area, the minimum width of a pedestrian island is 6’.13 The desired minimum width is 8’. If 6’ or wider, detectable warning surfaces must be placed at both sides of the island to distinguish the bikeway from the sidewalk, and the island from the bikeway.
• No Stopping/No Standing Zones: Zones should be long enough to allow approaching drivers and bike riders to see and recognize one another ahead of the intersection. Many cities already designate 20’-30’ of curb before an intersection as a no-standing zone to increase visibility. Features that permit visibility, such as plants, seating, bike parking, and shared micromobility stations, can be placed here.
• Bike Queue Areas: Queue areas should be large enough for anticipated bicycle volumes, which often increase substantially after implementation of protected bike lanes. The bike queue area should be at least 6.5’ deep, but dimensions of 10’ or greater are desirable to accommodate trailers, cargo bicycles, and high bike volumes.
• Accessible Signals: See MUTCD Chapter 4E, PROWAG, other national guidance, and local standards for signal timing and location guidance.
• Bike Yield Line & Bike Lane Crosswalk: Bike traffic should be expected to move forward to the stop bar on any signal phase, and pedestrian traffic should also be expected to cross to the island on any phase. This operation may be formalized with optional yield teeth on the bikeway before the crosswalk. The 2009 US MUTCD calls for a “Yield Here to Pedestrian” sign if yield teeth are used. In some jurisdictions, a yield line is not necessary before a crosswalk.
• Signs: A modified “Turning Vehicles Yield to Bikes and Pedestrians” sign (R10-15)17 is recommended where a signalized intersection allows right turns concurrent with bicycle and pedestrian movements. It is required in jurisdictions where state/provincial or local laws are such that pedestrians and bikes do not automatically have the right of way over turning vehicles. The sign should be mounted close to any signal head that regulates vehicles turning across the bikeway and any required location. (This modified sign remains experimental under the 2009 MUTCD.)