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SAFE Issue#10 - Alameda - Santa Cruz “Y” Intersection

Provides full Safety Issue details as PDFA critical Safety point is at the “Y” intersection of Santa Cruz and the beginning of Alameda de las Pulgas.   This intersection is unacceptably dangerous for cyclists, pedestrians, motorists, and those residents that have driveways there. 

--  This interactive comparison is of the 10.5 solution from this full section 10. It compares the community design to the current configuration of the "Y" intersection.

--  This Video shows a proposal for the removal of the dangerous short 3rd NB lane.

--  This Video shows the dangers for residents along the SantaCruz "Y" slip lane.

--  This Video shows an issue with the 3rd NB SCA lane being kept as nearly always Green light.

The Santa Cruz/Alameda Y interesection is one of the most complex and dangerous intersections in San Mateo County.  



Below is an interactive before/after view of option 10.5 which substatially improves the intersection by simplifing the design, reducing speed, and reducing the size of the intersection.  Areas in brown and light brown could be greenery or other taffic calming features - the darker gray areas are recovered areas that provide safety buffers by the redesign.


There are some layout issues that make the reading of the webpage a little confuing. Both main pictures (labeled map and collage of accidents) are reproduced twice.

I, for one, would start the discussion about lemonade stands and accidents in a fresh paragraph AFTER the map and before the accident collage.

Thursday, 8/18, 7:45am
Walking across Santa Cruz Avenue toward Campo Bello.
Pedestrian walk signal indicated I could cross, but the car coming from Santa Cruz part of the Y continued through the intersection.

Either the light and indicator changes too fast or the car ran the light. Either way, the intersection is unsafe for pedestrians.

Suggested remedies:
Stop all traffic when the pedestrian signal is pressed.

Delay the change in signals so cars and pedestrians are assured the other direction is stopped before proceeding

Flashing pedestrian signs

This is a residential street and there is no safe way for pedestrians (kids visiting friends houses) to cross from the East side to the West of Santa Cruz Avenue or to cross the "Y" to get to the East side of Alameda. The cars are driving way too fast and there is no marked crossing area. Currently, we have to cross toward Campo Bello and back across Alameda to walk on the West side of Santa Cruz Avenue.

Slowing down the Y off Alameda would be great. Not sure why people punch it when they come to this intersection, they are not going far as there is a four way stop. Maybe a few Silent Police (large speed bumps) may help.

About a year ago someone tried to pass me on the right, at the Santa Cruz-Alameda intersection.
Minor damage.

The street (Santa Cruz) does or did not clearly indicate lanes for south-bound & north bound vehicles. Some new painting has been done, but safety experts on lane painting would be welcome.

Accident at the Y Nov 29,2017 : This is the same thing that keeps happening at this intersection. Similar thing happened a few years back when a driver crashed into my stone wall at 2099 Santa Cruz Avenue, and of course at the house with the destroyed wall right at the Y. The only way I can think of preventing this is to put speed bumps or pavement bumps at the roads leading to the Y. Has that been discussed as an option at all?

For the crosswalks at the "Y" and SCA mid-black, the roads are very wide and there is much complexity at the sides of road. It is not easy for car drivers to see when a pedestrian is entering a crosswalk, especially from the other side of the road. As a car driver or a pedestrian I would like to see actuated light bumps for the crosswalks.

I am pretty sure a suggestion along the lines that follow has been made [see option 10.4] but I read a chapter in a book called Messy by Tim Harford that really crystallized it. See pages 201 to 204 regarding roundabouts. The gist is that the messiness of such a traffic pattern forces attention, slows speed and is ultimately safer.

There is a sight line issue from SB Alameda and EB Campo Bello. AASHTO Policy states "At signalized intersections, the first vehicle stopped on one approach should be visible to the driver of the first vehicle stopped on each of the other approaches". Vehicles from those two approaches cannot see each other.

Using the same criteria and comparing Saftey Option 10.5 to County Alt C design, the distance between the Campo Bello driver and the driver stopped on the SB Santa Cruz stop line is a meager 11' differential between to two designs, much smaller than a car length.   That is, Safety Option 10.5 measures out to be about 185' between the two drivers; for County Alt-C, it is 174' between the drivers.  That is such a nominal distance, that if there is a concern, the concern should be applied to both designs.  

I see that the SB Alameda distance to Campo Bello is, in the 10.5 option, about 2 car lengths longer than the current configuration.  From a line of sight perspective that is longer, but from an effective sight linel difference perspective that may be a minor issue.   In any case, that distance can be reduced by minor adjustments to how SB Santa Cruz enters the intersection.  The goal is to make a much slower curve on continuating Santa Cruz Ave connection, by  eliminating the current dangerous and high speed slip lane curve.   The additional 10.5  improvement of reducing the skew approach, as recommended by FHWA and other Traffic/Pedestrian safety organizations, allows the entire intersection to be less complex and much narrower intersection.  That allows for the woonerf pathway, makes for a calmer intersection overall, with much shorter crosswalks and addresses the blind corner, amongst other signficant safety improvements.

Additionally, AASHTO states that skewed approaches should be avoided, with the safest angle at 90° to 75°.  It appears that the severe angle of the Alt-C skew is NOT recommended by AASHTO.   Also, Federal Highway Administration (FHWA)  states that skewed intersections should be corrected to 90° (aka 'T' intersections) as skewed intersections have higher accident risk and resulting in more severe injuries, along with line of site issues.

Add to this that cars on the Safety Option 10.5 will be naturally restricted to a slower 25 mph max turn speed and the County Alt-C, based on the current fautly design, often has cars traveling well above 40 mph.  In this case, the Intersection Decision Sight Distance comes into play:  The computed sight distance for Safety Option 10.5 would be 152', well within the 185'  design parameters.  However, the County Alt-C has the potential, based on current speed experience, of having a computed 300'  to 400' decision sight distance because of the higher speed drivers often use in that configuration, well over twice that of Option 10.5.  

FHWA-Signalized Intersections 4.5.2

I think if you compare the safety improvements incorporated in the 10.5 design, you will find that that many of the key safety goals are not achieved in the Alt-C design.

I think you missed my point. The problem is you cannot see the other driver at Campo Bello when both vehicles are stopped at the sto bar. It doesn't matter if you are 10 feet away or 50 away. If you cannot draw a straight line from one stop bar to another without hitting an obstruction (house and trees), the design is disqualified. Therefore, the geometry of the intersection has to be adjusted to be viable. As it stands, this design fails to meet the minimum criteria and can't even be compared to others until it meets that criteria.

Thank you for clarifying and for the explaination.   At first I had thought you were talking about SB Santa Cruz, thus that reply.  When I re-read your original comment, I saw you were talking about SB Alameda.  As I pointed out, their is a difference of about 2 car lengths so I decided to take photos.  

While I see county's concern on the line of sight, it seems a bit strange that the exact issue expressed on the Safe 10.5 deisgn, is present in the current design and yet no apparent County concern- see photo.  

I agree that a tweak to the 10.5 are welcome and it appears that the main mitigation that would correct this issue for the current usage would address any further concern for the Safe 10.5.  I think solving for one solves for all.    Especially with the sidewalk being widened to the west, away from Santa Cruz, where further line of sight would be enhanced.

Current SB Alameda at Y intersection-Line of sight

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