Highway 101 Ramp Metering Lights at Rengstorff Ave in Mountain View Are Working Again
A few months ago, I wrote about a frustrating mystery on Highway 101: the ramp metering lights at Rengstorff Avenue in Mountain View had been dark for years — contributing to sudden slowdowns on southbound 101 right after the merge. You can read that earlier post here:
Good news — the lights are back on!
9/23/25 - video of the Rengstorff Ave Southbound Highway 101 on ramp metering lights working
In September, Caltrans confirmed that the issue at the Rengstorff on-ramp had been fixed, a couple days after I reported the issue. Aung M. Maung, Deputy District Director of Traffic Operations for Caltrans District 4, told me:
“Thank you so much for reaching out to us. I’d like to update you that Caltrans team conducted the site investigation and corrected the issue at Rengstorff on-ramp metering lights.”
The repair is part of a larger rollout of Caltrans’ Adaptive Ramp Metering (ARM) program, which dynamically adjusts the timing of ramp lights based on real-time freeway conditions. A Branch Chief from Caltrans Ramp Metering Operations explained:
“Yes, the Adaptive Ramp Metering (ARM) program has been rolled out for the SM/SCL-101 corridor, and this location is currently running the ARM program.”
If you’ve driven southbound recently, you may also notice that the ramp lights at Embarcadero Road in Palo Alto are on — the first time I’ve seen them active in nearly three years.
Why This Matters
Ramp meters may seem like an annoyance when you’re waiting to merge, but the data consistently shows they make a real difference. Caltrans and MTC report that adaptive ramp metering:
- Reduces congestion on the mainline freeway
- Makes merging smoother and safer
- Delivers more consistent and reliable travel times
According to Caltrans data, after Phase 2 of the ARM rollout (between Brisbane and Redwood City), morning travel times on 101 improved by about 20%, dropping from 25 minutes to 20 minutes. Evening travel times improved from 28 minutes to 25 minutes.
Across the Bay Area, freeway travel times have dropped sharply after metering was installed:
- I-580 (Foothill Rd → North Flynn Rd): down 37%
- US-101 (San Mateo → Palo Alto): down 30%
- I-80 (Red Top Rd → North Texas St): down 25%
- US-101 (Petaluma → Windsor): down 9%
(Source: MTC Adaptive Ramp Metering Program)
What’s Next
Phase 1 of adaptive ramp metering covered the stretch between Sunnyvale and Redwood City — which includes East Palo Alto. Phase 2, from Brisbane to Redwood City, launched in May 2025 (Caltrans press release). Phases 3 and 4 will extend the system further south.
Even though this update is about Mountain View, it has ripple effects for nearby cities like East Palo Alto. Highway 101 is our main corridor, and when bottlenecks appear — even 5 miles away — traffic and emissions spill back into our local streets. Every bit of efficiency on 101 helps reduce neighborhood cut-through traffic and air pollution here at home.
Broken Lights
There has been a regional trend of broken street lights, particularly on Caltrans property such as on highways. For instance, the street lights at our University Ave highway 101 northbound on ramp have been broken for years. The light under our University Ave vehicular bridge is also broken. I have had conversations with our public works maintenance team, who had submitted the issue multiple times to Caltrans over the past few years, and the lights continue to remain dark. The reasons are unknown; some people speculate it could be because of copper theft issues.
How You Can Help
If you see any issues, please report them directly to Caltrans maintenance. Many of the emails are not listed publicly, and I had to guess the email by using the format <first.last>@dot.ca.gov. I found that to be a lot more effective than emailing the District 4 Bay Area public information officer.