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.

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