Summary: The city should not install curb islands at corners, as it is currently doing, but rather install much safer and more effective true curb extensions, even if fewer can be installed now. Temporary installations can be used at other corners.

The City of Sacramento is currently re-doing a number of intersection corners in midtown. Most of these corners are along 21st Street, so far as I’ve noticed, but some are on other streets, and there well may be other locations I’ve not noticed yet. Last week crews were out saw cutting asphalt at corners, in preparation for new concrete work. The existing corner concrete and ramps have been removed from at least two corners, and at the 21St Street and O Street corner there is form work for whatever is going to replace the old corners.

The first photo is of the saw cuts at P Street & 19th Street. The cuts don’t really stand out, but they do indicate the areas that will be changed.

It appears from the saw cuts that what is going to be constructed is something similar to the existing northwest and northeast corners. Northwest is shown below. I am not sure what to call these. They are not in the city’s street design standards, and almost the only place where I’ve seen them is Sacramento. I looked at several other cities to see if these were in their street designs, and they were not. So, just to call them something, I’m going to call them ‘curb islands’. The City of Los Angeles calls these floating curb extensions, but apparently their intended use is with bike lanes, not with gutters.

I suspect that part of the reason the city likes this design is that it doesn’t require any change to the gutter drainage pattern. But as you can see from the photo above, that has issues. There is debris accumulated in the gutter, which cannot be removed by regular street sweeping, and could only be removed by manual labor. That is very unlikely. There are some street gutters and drains that are maintained by citizens, but most are not, and building something that depends on citizen maintenance is not a good idea.

The photo below is the one corner that seems to have active construction going on, concrete forms are being placed. Though it is hard to say for certain at this stage of work, it appears at though the curb line is not being changed, only curb islands being added.

So, why is this work being done? I suspect it is for two reasons:

• To install ADA-compliant curb ramps. There are very specific requirements for ADA-compliant curb ramps, including slope, width, and the detectable warning strips (the yellow bumps or truncated domes). Most corners in the central city do not meet current guidelines.
• To slow right-turning drivers. By reducing the turning radius of the corners, drivers are slowed slightly.

Is slowing drivers slightly an advantage for people walking and rolling? Sure, a little. But these curb islands do only a fraction of the good of true curb extensions.

A true curb extension is shown below. Note that construction was not complete and the detectible warning strips had not been installed. A true curb extension such as this greatly increases visibility between drivers and walkers, and significantly reduces the crossing distance for walkers. It also prevents drivers from parking over crosswalks, which is not common but is an issue in Sacramento. The FHWA Crash Reduction Factors does not include curb extensions, because it was last updated in 2008, but it does include ‘Restrict parking near intersections’, also accomplished by curb extensions, at 30 CRF, which is significant. FHWA has been reluctant to fund research on curb extensions, and so they are not in the more modern Crash Modification Factors. An Oregon student found “The findings of this research suggest that curb extensions contribute to a significant reduction in the average number of vehicles that pass a waiting pedestrian before yielding to the pedestrian.”

My recommendation is that the city NOT do these half-measure corners, but instead do true curb extensions. Are true curb extensions more expensive, Probably a little, with more concrete to be poured. The bigger issue, for some corners, is that gutter drainage and drain inlet locations may need to be changed, which can be quite a bit more expensive.

True curb extensions offer locations for trees, bioswales, and other sidewalk amenities, and can be extended to bus boarding islands for in-lane bus stops.

What to do instead? The city should do true curb extensions on the corners of intersections where there is a significant crash history with right-turning drivers, or driver failure to yield to walkers in the crosswalk. That means fewer intersections would be improved. What about the other intersections, which also need improvement. I recommend temporary curb extensions, with pavement paint and vertical delineators. One installation is shown below, on Land Park Drive and 8th Avenue. Not a very elegant one, but effective.

Street modifications with concrete are essentially permanent, in the sense that they are intended to last at least 30 years. So if the city installs half-measure corners, these will likely be in place for 30 years. For 30 years, they will provide less safety and encouragement for walkers than would be the case with true curb extensions.

Lastly, diagram showing why curb extensions are so important for visibility between drivers and walkers, the first from PedSafe, the second from NACTO.