I-280 Northbound Geneva Avenue Off-Ramp Study

New Signal Phasing and Timing Plan and Implementation

In summer 2022, the project team initiated existing conditions analysis of the northbound I-280 Geneva Avenue off-ramp traffic flow and ramp intersections traffic circulation to develop recommendations for future improvements. In summer 2023, the multi-agency study team developed signal timing changes (near-term recommendation) which was eventually successfully piloted, extending the study schedule.

Findings

The new traffic signal and phasing changes at the I-280 Geneva northbound and southbound ramps piloted by the project team improved the capacity of the I-280 northbound off-ramp and improved pedestrian safety at the I-280 southbound on-ramp, while maintaining east-west circulation including for Muni buses and light rail. 

• During the AM Peak Hour, the northbound off-ramp left lane flow rate (vehicles/second) improved from 0.25 to 0.34, a 36% increase in flow and the right lane flow rate improved from 0.27 to 0.30, an 11% increase. 
• During the PM Peak Hour, the northbound off-ramp left lane flow rate (vehicles/second) improved from 0.23 to 0.28, a 22% increase in flow and the right lane flow rate improved from 0.29 to 0.35, a 21% increase. 
• The new signal and phasing implementation also fixed a problematic pedestrian and vehicle conflict at the entrance to the I-280 southbound on-ramp. The new phasing removed vehicle conflicts with pedestrians crossing at the I-280 Geneva southbound on-ramp by changing the leading left turn signal for west-bound vehicles accessing the ramp to a lagging left turn.

Recommendations

The analyses and improvement measures identified in this study are the first steps in a longer-term process for improving Geneva Avenue in the Balboa Park station area. The study’s recommendations were informed by input from the Transportation Authority’s Community Advisory Committee and neighborhood groups. The recommended next steps include:

• (Already completed) Implementing the recommended near-term signal phasing improvements with the Caltrans District 4 signal operations group and SFMTA and analyzing the operational and safety changes.
• Pursuing the recommended mid-term traffic signal system modernization to replace the current aging system as it reaches the end of its life cycle. Scoping will consider:
  • Pursuing new overhead signal heads mounted on longer mast arms poles to improve visibility and may include elements of Intelligent Transportation Systems.
  • Pursuing potential street lighting improvement.
  • Exploring pedestrian bulbs, No Right Turn on Red signage, and other pedestrian safety and traffic management changes through the Transportation Authority’s Vision Zero Phase 3 Study and as part of next-phase scoping studies with Caltrans and SFMTA.
  • Collecting detailed topographic survey, utility, structural, and geotechnical data to facilitate preliminary engineering.
• Further study of Geneva northbound ramp queue spillback to the I-280 mainline and ways to address this, potentially via lane lengthening/re-alignment (straightening) to improve storage and visibility and advancing driver information systems to notify motorists of potential queues ahead.

September 10, 2024 Transportation Authority Board

September 10, 2024 Transportation Authority Board presentation (PDF)

Final Report

I-280 Northbound Geneva Avenue Off-Ramp Study Final Report (PDF)