• Skip to primary navigation
  • Skip to main content
  • Skip to primary sidebar

The Glen Park Association

Up-to-the-minute news from Glen Park

  • Home
  • Glen Park Association
    • About the Glen Park Association
    • Join the GPA
    • GPA Board Contacts
    • GPA Meeting Minutes
    • Bylaws
    • Neighborhood boundaries
  • News Stories
    • Glen Park News
    • Editor’s Picks
  • Greenway
    • About
    • Greenway Plan
  • GPA Grants Program
  • Crime & Safety
  • Contact
    • Contact
    • Volunteer Sign Ups
    • Event Submission
    • Author Submissions

Diamond/Bosworth update

June 19, 2015 by Elizabeth Weise

In the May 28 blog summary of the GPA’s transportation committee’s first meeting with SFMTA, traffic engineer Damon Curtis had promised to look into two things:

–creating simultaneous protected lefts northbound and southbound on Diamond

–switching the new protected northbound left on Diamond to be southbound in the evening to accommodate rush hour traffic

Neither option will be possible. The rationales given by SFMTA are summarized below (and Curtis’s full email is attached here).

One important term to note: LOS means “Level of Service,” a state standard that basically measures how many cars can be pushed through an intersection in a given time. It is graded from A to F. Its applicability is changing in a way that I didn’t totally understand, sorry to say (hw).

On creating simultaneous protected lefts northbound and southbound on Diamond:

Curtis modeled simultaneous protected northbound and southbound left turns with both a 90-second and a 120-second signal cycle. For the former, the intersection level of service [LOS] degrades to F and for the latter it degrades to E. Therefore both scenarios trigger a significant impact that would require additional, extensive environment review.

A protected NBLT does not degrade LOS to an E or an F because northbound traffic can still proceed straight through the intersection at the same time. (See more detail in the longer answer below.)

On switching the new protected northbound left on Diamond to be southbound in the evening to accommodate rush hour traffic:

 

Technology exists to allow for different left-turn phasing at different times of day to meet changing demand, but based on the traffic counts from the Glen Park EIR Traffic Impact Study which SFMTA used as the basis for its recent left-turn analysis, northbound left turn volumes far exceed southbound left turn volumes in both the AM and PM peak hours (229 versus 137 in the AM, and 210 versus 117 in the PM).

More from Curtis:

“In traffic signal timing we base the amount of green time for a given movement on the volume of cars and the movement that requires the most amount of green time is defined as the critical movement. If we base the timing on percentages, the intersection would not operate efficiently and inevitably one or more approaches would begin to back up.

“For the NBLT and SBLT at Diamond/Bosworth, the left-turns as a percentage of all traffic on their approach are about equal, but we know that beneath those percentages are real numbers and that the NBLT has a demand of 229 cars and the SBLT demand is 137 cars. That means the NBLT has 67% more vehicles than the SBLT. In addition, in the NB direction there are 243 vehicles going straight or turning right, but in the SB direction that total is only 165, i.e., the NB demand is 47% greater.

“And since cars going straight and cars turning right must share a single lane (the case for both NB and SB), it only takes having that first vehicle in the queue wanting to go straight to hold up all of the potential right-turners and therefore the expectation is that the majority of the straight thru and right-turn movements will occur only when the light is green.

“Taking all these factors together, we can begin to understand why the intersection Level Of Service breaks down when we introduce a protected SBLT phase – it’s primarily because during a protected SBLT phase, all of the NB straight thru and right turn traffic must be held back, then during the subsequent green phase we are unable to provide enough time to serve all of those vehicles, not to mention serving the demand for EB and WB, and still keep the overall signal cycle length below 120 seconds.”

 

GPA: What about congestion backflow into GP Village?

Curtis: “Regarding favoring southbound [protected left] over northbound because the effects of congestion are greater in the residential/commercial area north of the intersection than they are coming off the freeway to the south, I will start by saying say that when it comes to the signal timing at Diamond/Bosworth there is no magic bullet and there will be some trade-offs.

“I discussed this very point with Ricardo [Olea, City traffic engineer] and we both agree that when taking a more macro view of traffic operations at and around Diamond/Bosworth, there is little question that causing back-ups on NB Diamond (which having a protected SBLT would do) will negatively impact traffic on Monterey as far back as the freeway on/off-ramps at Monterey/Circular, and that would have a far greater impact on a much larger number of people than the alternative.”

[Note from Heather] If you’ve read this far, you’re a true geek and might want to check out this presentation from Ricardo Olea titled “Signal Timing and Pedestrians.”

http://nacto.org/wp-content/uploads/2013/10/OleaRicardo_DesigningCitiesPHX.pdf

Filed Under: Uncategorized

Primary Sidebar

IMPORTANT UPCOMING DATES

Upper Noe Neighbors Community Meeting Wednesday, May 21, 7 p.m.
Upper Noe Recreation Center auditorium
295 Day Street
Agenda


San Francisco Department of Public Works logoDPW Love Our City
District 8 Cleanup Day
Saturday, June 7, 9 a.m. to afternoon
Learn more and sign up here


 

Logo Center for Creative Exploration

The Center for Creative Exploration
Explore all the Colors of the Rainbow
one-day workshop
Saturday, June 7, 10 a.m. to 4 p.m.
300 Chenery Street
Learn more and link to registration here


Weeding Party
June 21, 10 a.m. to noon
100 block of Arlington at Charles
Join neighbors on the North end of the Cut to keep down the weeds and beautify top to bottom. Tools, lunch and good company provided.


Stop the bleed logoStop the Bleed Workshop
Thursday, June 26, 6-9 p.m.
St. Aidan’s Church
To learn more, click here


Monthly cleanup on the Greenway
First Saturday of the Month (usually)
Click here to learn more


Friends of Glen Canyon’s
Glen Canyon Habitat Restoration
Every third Saturday 9:30 a.m to noon
Sign up here

Subscribe to this Newsletter

Sign Up for Glen Park Association News Updates:

* indicates required

Check It Out at the Glen Park Library

Click the above button or here to see all upcoming Glen Park Branch Library events. Subscribe to our monthly newsletter to get events highlights in your inbox.

Glen Park Rec Center

Glen Canyon Park sign
Click here for latest
Glen Park Rec Center
class schedule


Saturdays 3-4:45 p.m.
Questions? Call 415-239-4007


GP Movie Night Schedule

Renew Your Glen Park Association Membership for 2025

Join the Glen Park Association and help promote our community’s interests. Together, we can secure improvement funds, publicize neighborhood concerns and strive to speak as one voice on neighborhood and city issues.

Membership in the Glen Park Association is only $10 annually and can be purchased online.

Glen Park Association Advertising Sponsors

JE_Digital Small Space Ad
Diamond Heights Digital Ad
GPA Ad- Perez Construction ad 6.27.22 v Glen Park
moroco
Center for Creative Exploration - adult
JE_Digital Small Space Ad
Diamond Heights Digital Ad
GPA Ad- Perez Construction ad 6.27.22 v Glen Park
moroco
Center for Creative Exploration - adult
previous arrow
next arrow
Shadow

Current Weather & Air Quality

Glen Park featured on…

FacebookSF ChronInstagramTwitter

Join the Glen Park Association on Facebook

Comments Box SVG iconsUsed for the like, share, comment, and reaction icons
Glen Park Association is at San Francisco Public Library Glen Park Branch.
2 days ago
Glen Park Association

Photos and Fun courtesy of the Glen Park Library!
It was a great turnout at the Glen Park Library Open House on Saturday May 17th!

Thank you to all who attended and a big thank you to Glen Park Branch Library Manager Darren Heiber and his staff for a fantastic day!! 🙌🏽

San Francisco Public Library Arion Press | Artist Books Museum of Craft and Design Rafael Mandelman 🏳️‍🌈 #glenparklibrary #arionpress #museumofcraftanddesign #glenparksf #sanfrancisco #InCommunity
... See MoreSee Less

Photos and Fun courtesy of the Glen Park Library! 
It was a great turnout at the Glen Park Library Open House on Saturday May 17th!

Thank you to all who attended and a big thank you to Glen Park Branch Library Manager Darren Heiber and his staff for a fantastic day!! 🙌🏽

@sfpubliclibrary @arionpress @museumofcraftanddesign @rafaelmandelmand8 #glenparklibrary #arionpress #museumofcraftanddesign #glenparksf #sanfrancisco #incommunity
View on Facebook
· Share
Share on Facebook Share on Twitter Share on Linked In Share by Email
View Comments
  • likes 0
  • Shares: 0
  • Comments: 0

0 CommentsComment on Facebook

Glen Park Association is at Glen Park Recreation Center.
3 days ago
Glen Park Association

Qi Gong & Tai Chi Thursdays at the Glen Park Rec Center!

Thursdays 2:00PM - 2:45PM
Room #1
Led by led by Ashima Sarin

Beginners and All Levels of Mobility Are Welcome! It’s FREE and drop-in!

(There will be no class the second half of June and July)

📍Glen Park Rec Center, 70 Elk Street

QUESTIONS? CALL 415-239-4007
... See MoreSee Less

Qi Gong & Tai Chi Thursdays at the Glen Park Rec Center!

Thursdays  2:00PM - 2:45PM 
Room #1
Led by led by Ashima Sarin

Beginners and All Levels of Mobility Are Welcome! It’s FREE and drop-in! 

(There will be no class the second half of June and July)

📍Glen Park Rec Center, 70 Elk Street 

QUESTIONS? CALL 415-239-4007
View on Facebook
· Share
Share on Facebook Share on Twitter Share on Linked In Share by Email
View Comments
  • likes 4
  • Shares: 0
  • Comments: 0

0 CommentsComment on Facebook

Blog Roll

Coyote Yipps
Friends of Upper Noe Recreation Center
Glen Park Neighborhoods History Project
Open SF History
Sunnyside Conservatory
Sunnyside History
Sunnyside Neighborhood Association
Tramps of San Francisco
Upper Noe Neighbors

Copyright © 2025 · Metro Pro on Genesis Framework · WordPress · Log in